Marconi TF 2600B Service and user manual

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Page 1

Instruction Manual No. H52600-920L for

Video Voltmeter TF 2600B

Model No. 52600-920L

RADIO FREQUENCY INTERFERENCE

This equipment conforms with the requirements of EEC Directive 76/889 as to limits of r.f. interference.

MARCONI INSTRUMENTS LIMITED ST. ALBANS HERTFORDSHIRE ENGLAND

H 5 2 600-920L 1f - 9/84

MI 0.8c 9/84/H

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Chapter 1 GENERAL INFORMATION

1.1	Introduction	•	•••	3
1.2	Data summary	•	•	4
1.3	Accessories supplied	•		5

Chapter 2 OPERATION


2.1	Preliminary requirements	6
2.2	AC supply cable	6
2.3	Fuse	6
2.4	Controls and connectors	6
2.5	Voltage measurements	6
	2.5.1 Sinusoidal waveforms	6
	2.5.2 Noise levels	7
	2.5.3 Non-sinusoidal waveforms	7
	2.5.4 Determination of dBm	7
2.6	Power measurements	7
2.7	Using TF 2600B as an amplifier	7
2.8	DC output	8
2.9	Input and output connectors	8

Chapter 3 TECHNICAL DESCRIPTION

3.1	Mecha	nical characteristics	•	g
3.2	Circui	t summary	•	9
3.3	Circui	t functions	•	10
	3.3.1	Input attenuator	•••	10
	3.3.2	Overload protection	circuit	10
	3.3.3	First amplifier	•••	10
	3.3.4	Inter-amplifier atten	uator	10
	3.3.5	Second amplifier	•••	11
	3.3.6	Final amplifier and d	liode
		bridge rectifier	•••	11
	3.3.7	Power supply		11

Chapter 4 MAINTENANCE

4.1	Introduction		•	12
4.2	Screw fasteners		•	12
4.3	Access to sub-assembli	ies ar	nd
	components	•	•	12
4.4	Preliminary checks		•••	12
4.5	Test equipment	•	•	12
4.6	Performance checks	•	•••	12
	4.6.1 Power supply	•	•••	12
	4.6.2 Noise check		•••	13
	4.6.3 Voltage range ch	neck	•••	13
	4.6.4 Voltage scale ch	eck	•	14
	4.6.5 Frequency respo	onse	•	15
	4.6.6 AC output voltag	e	•	15
4.7	Cleaning rotary switche	s		15

Chapter 5 REPAIR

5.1	Introdu	lction	•	•	•	16
5.2	Fault f	finding	•••	•	•••	16
	5.2.1	Circuit	t voltage	es	•••	16
	5.2.2	Signal	levels	•	•••	16
	5.2.3	Power	supply	•	•	16
	5.2.4	Voltage	e range	check	•••	17
	5.2.5	Voltage	e scale	check	•	17
	5.2.6	Freque	ency res	ponse	•••	17
	5.2.7	AC out	put	•		18
	5.2.8	Noise 1	level	•	•••	18

Chapter 6 REPLACEABLE PARTS

Introduction and ordering ...

Chapter 7 CIRCUIT DIAGRAMS

Circuit no	otes	24
Fig. 7.1	Input and intermediate stages	25
Fig. 7.2	Metering, output and power supply	27

Page 3

Chapter

General information

1.1 INTRODUCTION

TF 2600B is a wide band a.c. voltmeter which can also be used as a power meter, an a.c. to d.c. converter and an amplifier within the frequency range 10 Hz to 10 MHz. With a suitable test arrangement it can be used to measure the frequency response of pick-ups, tape heads, r.f. or a.f. amplifiers, filter networks, or the low level outputs from transducers such as strain gauges.

As a power output meter in conjunction with a signal generator, it can be used to check receiver sensitivity, receiver bandwidths, signal to noise ratio, the response of s.s.b. receivers or the attenuated outputs from signal generators.

Twelve switched voltage ranges provide fullscale meter indications from 1 mV to 300 V. The large linear voltage scales give a discrimination of 10 µV on the 1 mV range and there is also a scale calibrated in dB relative to 1 mW into 600 Ω.

Fig. 1.1 Video voltmeter type TF 2600B

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General information

1.2 DATA SUMMARY

AC VOLTAGE RANGES: 1, 3, 10, 30, 100 and 300 mV and 1, 3, 10, 30, 100 and 300 V f.s.d. ACCURACY AND FREQUENCY RESPONSE (at 23 °C +5 °C) : ± (% of f.s.d. + % of reading). 10Hz 30 Hz 2.5 MHz 4 MHz 10 MHz 10 mV to 100 V ranges : ±(1+2) ±(.5 + .5) $\pm(1+1)$ $\pm(1+2)$ 10 Hz 30 Hz 1 MHz 10 MHz ±(1+2) ±(1+1) ±(1+2) 3 mV range : 4 MHz 10 Hz 30 Hz 500 kHz 1 mV range : ±(1+2) $\pm(1+1)$ ±(1+2) 10 Hz 30 Hz 2.5 MHz 4 MHz 10 MHz ±(1+2) ±(1+2) ±(1+3) 300 V range : ±(1+1)

METER

Calibration :	Calibrated in r.m.s. value of a sine wave. (Responds to average value.)
Voltage scale :	Linear 137 mm long. Calibrated from 0 to 1.0 with 100 minor divisions and 0 to 3.0 with 60 minor divisions.
dB scale :	Calibrated from +2 to -12 dBm into 600 $\Omega$ . 0 dBm corresponds to 0.775 V.

INPUT

Input impedance :	1 mV to 1 V ranges : 10 MΩ in parallel with 25 pF ±10%.
	3 V to 300 V ranges.: 10 MΩ in parallel with 15 pF ±10%.
Maximum safe input :	1 mV to 1 V ranges :
	300 V r.m.s. from 10 Hz to 1 kHz,
	150 V r.m.s. from 1 kHz to 10 kHz,
	30 V r.m.s. from 10 kHz to 10 MHz.
	3 V to 300 V ranges :
	300 V r.m.s. from 10 Hz to 3 MHz.
	100 V r.m.s. from 3 MHz to 10 MHz.

DC OUTPUT	From rear panel terminals.
Level :	Not less than 1 V e.m.f. at f.s.d.
Source impedance :	Approximately 10 kΩ.

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AC OUTPUT	From rear panel BNC socket.
Level :	10 mV to 300 V ranges : at least 50 mV at f.s.d. into 50 \Omega.
	1 mV and 3 mV ranges : at least 5 mV at f.s.d. into 50 Ω.
Source impedance :	50 Ω nominal.
Frequency range :	10 Hz to 10 MHz.
POWER REQUIREMENTS
AC supply :	95 to 130 V or 190 to 264 V, 45 to 500 Hz, 7 VA.

DIMENSIONS AND WEIGHT	Height	Width	Depth	Weight
	132 mm	204 mm	255 mm	3.0 kg
	(5 1/4 in)	(8 in)	(10 in)	(6 3/4 lb)

1.3 ACCESSORIES SUPPLIED

Mains cable 43129-071D.

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Chapter

Operation

2.1 PRELIMINARY REQUIREMENTS

Before connecting the instrument to the a.c. supply :

(1) Check that the voltage switch is set to accept the local supply, either 95 to 130 V or 190 to 264 V. (Voltage regulation eliminates transformer tap changing within the selected range.) To change the range, remove the locking plate, set the switch correctly, reverse plate and refit.

(2) Check that the fuses are of the required rating - see Sect. 2.3 - and secure in their holders.

(3) If necessary, adjust the meter screw to set the meter pointer at mechanical zero.

2.2 AC SUPPLY CABLE

The a.c. supply cable is fitted at one end with a connector which mates with the plug on the instrument. When fitting a supply plug ensure that the conductors are connected as follows :

Earth - Green/Yellow
Neutral - Blue
Live - Brown

2.3 FUSES

The instrument is normally supplied with two fuses rated at 50 mA and with the mains selector switch set for supply voltages in the range 190 to 264 V. For mains voltages of 95 to 130 V change the fuses for those rated at 100 mA. Replacement fuses should be slow-blow (time lag type).

2.4 CONTROLS AND CONNECTORS

Front panel

AC SUPPLY switch. Positioned UP to switch ON.

PILOT LAMP (neon). Lit when a.c. supply is switched ON.

RANGE switch. Selects the required voltage or dBm range. For dBm measurements add (algebraically) the RANGE switch setting to the meter reading.

INPUT connector. 50 Ω BNC type.

Rear panel

MAINS INPUT connector. Accepts a.c. supply cable type 43129-071D supplied.

VOLTAGE SELECTOR switch. Selects either 95 to 130 V or 190 to 264 V to suit local a.c. supply.

AC OUTPUT connector. 50 Ω BNC type. Provides output proportional to a.c. input. The gain of the amplifier is dictated by the position of the RANGE switch.

DC OUTPUT terminals. Provide floating d.c. output proportional to the a.c. input. The output is extremely linear and allows TF 2600B to be used as an a.c. to d.c. converter.

FUSES. Mains input fuses rated at 50 mA (time lag) for 190 to 264 V or 100 mA (time lag) for 95 to 130 V.

2.5 VOLTAGE MEASUREMENTS

CAUTION The maximum allowable a.c. input depends on frequency – see Data Summary for limiting values. Note that when measuring a.c. superimposed on d.c., there is an additional limitation that the sum of the d.c. and peak a.c. voltages must not exceed 420 V.

2.5.1 Sinusoidal waveforms

The meter responds to the average value of an applied waveform but is calibrated in the r.m.s. value of a sine wave. Voltage levels up to 300 V are measured by connecting a low capacitance cable or low capacitance probe to the INPUT socket and by setting the RANGE switch to cover the expected level. The voltage (r.m.s.) is then given by the RANGE switch setting (f.s.d.) and meter indication.

2600-920 (1b)

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2.5.2 Noise levels

On the 1 mV range the meter pointer has, typically, an 18 µV noise deflection when the INPUT is connected to a source impedance of 1 kΩ or less, rising to a 23 µV deflection when connected to an impedance greater than 10 MΩ.

For voltages above 200 µV the noise levels can usually be ignored but for voltages below 200 µV the noise levels should be taken into consideration, the signal voltage being more accurately determined by

Signal voltage = $\sqrt{V1^2 - V2^2}$

where V1 = indicated signal level and V2 = noise level.

2.5.3 Non-sinusoidal waveforms

Waveform distortion has little effect on meter reading accuracy. From Table 2.1 it will be seen that even with the extreme examples of square and triangular waveforms the inaccuracy of the r.m.s. value does not exceed 10%.

The true r.m.s., average or peak value in each case is obtained by multiplying the meter reading by the appropriate factor.

Та	Ы	e	2	1
- a		•	£

	RMS	Average	Peak
	value	value	value
Sinusoidal	Correct	Reading	Reading
waveforms	reading	x 0.9	x 1.414
Square	Reading	Reading	Reading
waveforms	x 0.9	x 0.9	x 0.9
Triangular	Reading	Reading	Reading
waveforms	x 1.04	x 0.9	x 1.8

2.5.4 Determination of dBm

Although the dBm meter scale in conjunction with the range switch is directly applicable to an impedance of 600 Ω, the dBm calibrations can, with correction, be used for signal levels associated with impedances other than 600 Ω. Nominal

dBm corrections for some common impedance values are given in Table 2.2; these corrections should be added to the meter reading.

Table 2.2

Impedance	dBm correction
8Ω	+19
15 Ω	+16
50 Ω	+11
75 Ω	+9
1 kΩ	-2.5

2.6 POWER MEASUREMENTS

Since the meter is calibrated to indicate the r.m.s. level of a sine wave it can be used to determine the output power of r.f. receivers, r.f. amplifiers or a.f. amplifiers operating within the frequency range 10 Hz to 10 MHz.

For receivers, the voltmeter INPUT is usually connected to the loaded secondary winding of the output transformer or loudspeaker extension sockets or, if the loudspeaker is disconnected, to a suitable dummy load. The signal input to the receiver, consisting of a modulated carrier at some predetermined level, is normally obtained from a signal generator.

The output power is then determined by $\frac{V^2}{R}$

where V = the indicated voltage

and R = the impedance of the loudspeaker speech coil or dummy load.

2.7 USING TF 2600B AS AN AMPLIFIER

TF 2600B can be employed as a general purpose wide band amplifier. This enables low signal voltages to be increased to a level sufficient to drive a frequency counter or similar equipment. Used in this way, on ranges above 3 mV, at least 100 mV (r.m.s.) e.m.f. is available from a 50 Ω source when the meter pointer is at full-scale. On the 1 mV and 3 mV ranges the output is not less than 10 mV at full-scale.

The signal is connected to the INPUT socket and the amplified signal is obtained from the AC OUTPUT socket at the rear.

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2.8 DC OUTPUT

A floating d.c. output proportional to the signal level at the INPUT is available from the DC OUTPUT terminals at the rear. The d.c., which is at least 1 V e.m.f. (when the pointer of the meter is at full-scale) from a 10 kΩ source, can be applied to a digital voltmeter to supplement the meter indications and improve measurement resolution. Alternatively it can be used to drive a recorder.

2.9 INPUT AND OUTPUT CONNECTORS

The outer connector of the INPUT socket is isolated from chassis by a 10 \Omega resistor with a 0.1 \mu F shunt capacitor. This has the effect of breaking up unwanted earth current loops when the voltmeter is connected to one or more external sources. It is, therefore, unnecessary to disconnect earth leads from the equipment under test unless the highest possible accuracy is required in low voltage measurement. For the same reason the outer connector of the AC OUTPUT socket is isolated from the 0 V line by a 4.7 \Omega resistor.

When connecting a digital voltmeter (d.v.m.) or recorder to the DC OUTPUT, the connected instrument must have a balanced input or be capable of floating, i.e. neither terminal connected to earth. Using a digital voltmeter it is preferable, although not essential, to employ the d.v.m. interface network shown in Fig. 2.1. By adjustment of R4 the d.v.m. can be set to read exactly 1-0-0-0 at full-scale deflection on the TF 2600B. The 27 kΩ resistors are included to overcome small errors which would be introduced at high frequencies by the added capacitance.

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Technical description

This chapter, which outlines the overall and circuit functions of TF 2600B, is intended to be read with reference to the circuit diagrams in Chap. 7 and the block schematic diagram, Fig. 3.1.

3.1 MECHANICAL CHARACTERISTICS

Construction consists of a one piece chassis which supports a front panel and mounts a printed circuit board. The printed circuit board comprises three amplifier sections and the power supply rectifier/regulator.

Four vertical plates are mounted on the board to provide the required interstage screening which is completed by an overall screening plate fitted to the underside of the board.

The rear part of the chassis serves as a back panel onto which is mounted the DC OUTPUT terminals, AC OUTPUT connector, MAINS INPUT connector, AC VOLTAGE SELECTOR switch and the FUSE with the mains transformer mounted on the inside.

The front panel accommodates the METER, RANGE switch, signal INPUT connector, MAINS SUPPLY switch and pilot lamp. The instrument is contained within a standard 'Metrak' case fitted with a prop which can be hinged forward to tilt the instrument for easy meter reading.

3.2 CIRCUIT SUMMARY

The measurement system of TF 2600B consists basically of a three stage wide band amplifier followed by a full-wave average responding detector circuit which operates a meter. The first amplifier is preceded by a frequency compensated 0, 40 or 50 dB attenuator dependent upon the selected range and an overload protection circuit. For signal levels up to 1 V the attenuator is at 0 dB so the attenuator serves only to define the input impedance of 10 MΩ. On the 3, 10, 30 and 100 V ranges the attenuator provides 40 dB attenuation and on the 300 V range 50 dB attenuation. The overload protection circuit is included to prevent damaging voltage levels (above 10 V p-p) being applied to the gate of transistor TR1.

Transistors TR1, TR2 and TR3 provide an approximate overall voltage gain of 1.5 (3.5 dB). Output from TR3 is passed to a second attenuator providing an attenuation of 0, 10, 20, 30 or 40 dB determined by the setting of the range selector.

The second amplifier TR4, TR5, TR6 and TR7 consists of a feedback pair with TR5 and TR6 connected as a cascode amplifier followed by an emitter follower TR7. Both a.c. and d.c. negative feedback is incorporated and the amplifier provides a nominal voltage gain of 11.0 (20.8 dB).

Fig. 3.1 Block schematic diagram

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Output from the second amplifier is applied through TR9 to the AC OUTPUT connector and to a final amplifier TR8, TR10, TR11 and TR12. The circuit configuration of this amplifier is similar to that of the second amplifier without d.c. feedback. Output from the final amplifier is applied to a diode bridge circuit D8 and D9 which operates the meter and also serves to provide a d.c. voltage at the DC OUTPUT connector which is proportional to the a.c. input at SK1.

Each amplifier and the diode bridge system incorporates circuits to maintain the required overall frequency-response-(10 Hz-to-10-MHz) whilst filters are connected in series with the +30 V supplies to ensure that spurious r.f. signals are not introduced.

3.3 CIRCUIT FUNCTIONS

Block schematic diagram Fig. 3.1 interrelates the various circuits employed in TF 2600B whilst the sections which follow briefly explain the operation of each.

3.3.1 Input attenuator

Circuit diagram Fig. 7.1

The attenuator is at 0 dB for ranges 1 mV to 1 V. For ranges 3, 10, 30 and 100 V it provides for an attenuation of 40 dB and for the 300 V range an attenuation of 50 dB at all frequencies within the range 10 Hz to 10 MHz. To achieve this the RC time constant of the upper (series) section R7/C7/ C8 is designed to be the same as the lower (shunt) section consisting of R1/C2, R2/C3, R3/R4/R5/R6 and C4 in series with C5/C6. At low frequencies the division ratio is determined by the resistors. At high frequencies the division ratio is determined by the capacitors.

3.3.2 Overload protection circuit Circuit diagram Fig. 7.1

If the signal level at the junction of R9 and C10 exceeds 10.5 V p-p diodes D1 and D3 conduct to prevent excessive voltage being applied to the gate of TR1. For signal levels below 10.5 V p-p diodes D1 and D3 are non-conducting since they are biased off respectively by +4.7 V from D2 and -4.7 V from D4.

When D1 and D3 are conducting the signal voltage is developed across C1 at low frequencies and across R150 and R9 at high frequencies. At intermediate frequencies the signal voltage is developed across C1, R150 and R9.

3.3.3 First amplifier

Circuit diagram Fig. 7.1

The input signal at R9 is first amplified by the field effect_transistor TR1 and then by TR2. Negative feedback routed through C13 is developed across R13. Resistor R13 bootstraps the low noise resistors R11 and R12 so the effective input resistance of the amplifier is high.

Output from TR2 is applied to emitter follower TR3 which provides the desired low impedance for the 0, 10, 20, 30, and 40 dB attenuator.

3.3.4 Inter-amplifier attenuator

Circuit diagram Fig. 7.1

This consists of potential dividers using precision metal film resistors with capacitive correction to ensure a satisfactory 10 Hz to 10 MHz response. When the range selector is set at 1 mV, 3 mV or 10 mV the attenuator is at 0 dB. Resistors R23 and R24 are shorted so the output of TR3 'sees' the 15.2 kΩ input resistance (at 400 Hz) of TR4 in parallel with R21.

With the range selector at 30 mV or 3 V a 10 dB attenuation is introduced. Resistors R23 and R24 are inserted and connected in parallel with the combination R25, R26 to form the upper section of the attenuator. The lower section which is shunted by the 15.2 kΩ input of TR4 is primarily determined by R27 and R28.

For ranges 100 mV or 10 V a 20 dB attenuation is introduced. Resistors R23 and R24 are inserted to form the upper section with the lower arm again determined by R27 and R28.

For ranges 300 mV or 30 V an attenuation of 30 dB is introduced. Resistors R23 and R24 forming the upper section with the lower section determined by R30 and R31. For ranges 1 V, 100 V and 300 V resistors R23 and R24 form the upper section with the lower section determined by R32 and R33.

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3.3.5 Second amplifier

Circuit diagram Fig. 7.1

Output from the first stage, TR4, is applied to a cascode amplifier TR5 and TR6. High level d.c. negative feedback is introduced by R38 and R45 with a.c. negative feedback determined by R40 in parallel with R41 in series with R42.

Virtually all the voltage gain is produced by the cascode stage whilst the d.c. negative feedback ensures that the overall gain of the amplifier remains constant with variation of temperature and component value change due to aging.

When the range selector is at 1 mV, capacitor C30 is switched out of circuit. C28 and C29 together with the 15.2 kΩ input resistance of TR4 then provide attenuation at 10 Hz to compensate for increased amplifier gain at this frequency. For the 3 mV range C31 is connected into circuit to correct the 10 Hz response.

Output from the cascode state is passed to the final amplifier through emitter follower TR7 and through TR7 to emitter follower TR9 to serve the AC OUTPUT connector.

3.3.6 Final amplifier and diode bridge rectifier

The signal level to the base of TR8 is compared with the negative feedback voltage developed across R66 (10 mV range and above) which is applied to the emitter of TR8. This results in the difference being amplified to maintain constant the current through R66 and also the current through the diode bridge circuit D8 and D9 regardless of diode impedance and temperature changes.

The cascode circuit TR10 and TR11 together with the emitter follower circuit TR12 is essentially the same as that employed in the second amplifier. Open loop voltage gain is approximately 115 at 400 Hz and, since R63 is bootstrapped by TR12, the meter bridge is served from a high impedance source.

Diodes D8 and D9, which have a low forward resistance, are biased to be partially conductive by appropriate application of a positive and negative bias supply to resistors R70 and R78. The voltage across the resistors is determined by the current through R79 for the positive bias and through R69 and R84 for the negative bias. Resistor R76, connected across the bridge, sets the operational point of diodes D8 and D9 and also presents a definite source resistance to ME1.

For the 1 mV range R66 is shunted by R67 and R71 in parallel to increase the closed loop gain of the amplifier by 20 dB. With the series tuned circuit R75, L5, C65 incorporated to maintain the bandwidth, resistors R72 and R74 in parallel with R73 across R66 increase the gain of the amplifier by an approximate 10 dB for the 3 mV range with the frequency response corrected by the tuned circuit R152, C101, L10 and C67.

3.3.7 Power supply

Circuit diagram Fig. 7.2

The power supply provides stabilized d.c. voltage outputs of +30 V and -9 V.

The 30 V supply which has a degenerative regulator TR13, TR15, TR16, TR17 with Zener diodes D10 and D11 as the reference, is used to drive the amplifiers. The -9 V supply regulated by Zener diode D13 provides the negative bias to detector diodes D8 and D9. The power supply incorporates a 'foldback' circuit to prevent damage should a short-circuit be presented to the output of the regulator. As the output current rises the voltage across R83 increases, turning on TR14, which robs TR15 and TR13 of base drive, and thus reduces the output short-circuit current to a low value. Damage to TR13 by over-dissipation is thus avoided. AC inputs to the two circuits are obtained from two separate secondary windings on the mains transformer T1

A full-wave rectifier serves the +30 V regulator with a half-wave rectifier used for the 9 V supply. The mains transformer is connected to the a.c. supply through fuses FS1 and FS2, a two pole on/off switch SB, r.f. filter (X30 and X31, C102, C103) and a three pin connector. A neon lamp connected in series with a resistor across one primary winding of T1 is employed as the on/off indicator.

Page 12

Chapter

Maintenance

4.1 INTRODUCTION

This chapter contains information for keeping the equipment in good working order and for checking its overall performance.

Before attempting any maintenance on the voltmeter you are advised to read the preceding technical description.

CAUTION The instrument uses semiconductor devices which, although having inherent long term reliability and ruggedness, can be damaged by overloading, reversed polarity and excessive heat or radiation. Avoid prolonged application of soldering irons and ensure that, before breaking or shorting a circuit, damage will not occur.

4.2 SCREW FASTENERS

The majority of screw threads used in the instrument are metric of various sizes but in some positions BA threads are used. All chromium plated screws and all screws tinted blue are metric. Ensure that screws removed are refitted in the original positions.

4.3 ACCESS TO SUB-ASSEMBLIES AND COMPONENTS

The case is in two sections. To remove it take out the six screws at the rear of the instrument and then slide off top and bottom sections.

Direct access to all components is obtained when the case is removed. To replace a faulty component access to the underside of the board is obtained by removing the four screws holding the screening plate.

4.4 PRELIMINARY CHECKS

Prior to connecting the instrument to the a.c. supply :-

(1) Check to ensure that all switches are

undamaged and operating correctly and that all connectors are securely mated.

(2) Check that the fuses are of the correct rating and type and secure in the holders.

(3) Check that the meter pointer is at mechanical zero and if necessary adjust the meter screw to obtain this requirement.

4.5 TEST EQUIPMENT

The test equipment required for maintenance checks or repair is listed in Table 4.1.

4.6 PERFORMANCE CHECKS

It should be noted that test methods given in this section are simplified and of restricted range compared with those necessary to demonstrate complete compliance with the specification. They are intended only as a check procedure to determine if adjustment or repair is required. Performance limits given are for guidance only and should not be accepted as guaranteed performance specifications unless they are also quoted in the Data Summary, Sect. 1.2.

Performance checks given in Sections 4.6.2 to 4.6.6 must be made with the instrument in its case. Where adjustment is necessary, temporarily remove the top section of the case and replace it to recheck. Keep the instrument away from sources of interference.

If the results quoted are not obtainable, refer to the related section in Chapter 5.

4.6.1 Power supply

Test equipment : items a, b, c, d.

(1) With the instrument removed from its case, connected to the a.c. supply and switched on, check that the panel lamp is lit. Then allow not less than fifteen minutes for the instrument to thermally stabilize.

2600-920 (1a)

Page 13


ltem	Description	Recommended model
а	Multimeter	GEC Selectest.
b	Oscilloscope, 10 MHz	•
с	1 kΩ, ¼ W screened resistor
d	Digital voltmeter	Fenlowe type 931B.
е	DVM interface	See circuit, Fig. 2.1.
f	AF generator	General Radio type 1311A.
g	AC differential voltmeter	Fluke type 931B.
h	Ratio standard	Singer type 1011.
i	Frequency synthesizer, 400 Hz to 10 MHz	Hewlett Packard type 3320B.
j	T connector, BNC, with 50 Ω load

Table 4.1

(2) Connect the 1 kΩ screened resistor to the INPUT socket. Then, using the multimeter connected across C68 check that the voltage is between +29 and 31 V.

(3) Connect the multimeter across D13 and check that the voltage is between +8.75 and 9.75 V.

(4) Connect the digital voltmeter between the +DC OUTPUT terminal and the chassis and check that the digital voltmeter indicates 0 V ±10 mV. If not, adjust R84 slowly, allowing a settling time of about 10 s for each adjustment.

(5) Connect the oscilloscope across C68 and check that the amplitude of the 50/100 Hz ripple waveform is less than 1.5 mV p-p.

(6) Connect the oscilloscope across D13 and check that the amplitude of the 50/100 Hz ripple waveform is less than 20 mV p-p.

4.6.2 Noise check

Test equipment : item c.

(1) Connect the 1 k Screened resistor to the INPUT socket.

(2) Set the RANGE switch at 1 mV and check that the meter indicates less than 25 µV.

4.6.3 Voltage range check

Test equipment : items d, e, f, g, h.

(1) Connect the test equipment as shown in Fig. 4.1.

(2) With the TF 2600B switched off for at least3 minutes ensure that its meter pointer is at zero.If necessary, adjust the meter screw to set the pointer correctly.

(3) Switch the equipment on and allow fifteen minutes for the instruments to stabilize.

(4) Check and if necessary adjust the null setting of the differential voltmeter.

(5) Using the differential voltmeter, set the output of the a.f. generator at 1 V ±1.5 mV at 400 Hz.

(6) Set the ratio standard at .0100000.

(7) Set the TF 2600B RANGE switch at 10 mV.

(8) Check that the pointer of the TF 2600B meter is at full-scale, i.e. 1.0 V. If necessary, adjust R42 to set the pointer correctly.

(9) Adjust R4 in the d.v.m. interface to obtain a display of 1-0-0-0 V on the digital voltmeter.

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Fig. 4.1 Test gear arrangement for voltage range check

(10) Ensure that output from the a.f. generator is at 1 V ±1.5 mV. Set the ratio standard at .1000000 and the TF 2600B RANGE switch at 100 mV then check that the d.v.m. displays 1-0-0-0 V ±0.3%. If necessary select a value for R23 to obtain this requirement.

(11) Set the ratio standard at .0010000 and the TF 2600B RANGE switch at 1 mV then check that the d.v.m. displays 1-0-0-0 V ±0.3%. If necessary, adjust R71 to obtain the requirement.

(12) Check that the output of the a.f. generator is 1 V ±1.5 mV. Set the ratio standard at x000000 and the TF 2600B RANGE switch at 1 V then check that the d.v.m. displays 1-0-0-0 V ±0.3%. If necessary select a value for R32 to obtain this requirement.

(13) Check that the output of the a.f. generator is 1 V ±1.5 mV. Set the ratio standard at .0316200 and the TF 2600B RANGE switch at 30 mV then check that the d.v.m. displays 1-0-0-0 ±0.3%. If necessary select a value for R25 to obtain this requirement.

(14) Check that the output of the a.f. generator is 1 V ±1.5 mV. Set the ratio standard at .3162000 and the TF 2600B RANGE switch at 300 mV, then check that the d.v.m. displays 1-0-0-0 ±0.3%. If necessary select a value for R30 to obtain this requirement.

(15) Check that the output of the a.f. generator is 1 V ±1.5 mV. Set the ratio standard at .0031620 and the TF 2600B RANGE switch at 3 mV then check that the d.v.m. displays 1-0-0-0 ±0.3%. If necessary adjust R72 to obtain this requirement.

(16) Using the differential voltmeter set the a.f. generator for an output of 100 V ±150 mV at 400 Hz. Set the TF 2600B RANGE switch at 10 V

and the ratio standard at .1000000. Check that the d.v.m. displays 1-0-0-0 and that the pointer of the TF 2600B meter is at full-scale. If necessary adjust R6 to obtain the requirement.

(17) Check that the a.f. oscillator output is 100 V ±150 mV at 400 Hz. Set the TF 2600B RANGE switch at 300 V and the ratio standard at X000000. Check that the d.v.m. displays 0-3-1-6-Z. If necessary adjust R4 to obtain this requirement.

4.6.4 Voltage scale check

Test equipment : items d, e, f, g, h.

(1) Connect the test equipment as shown in Fig. 4.1.

(2) Repeat 4.6.3 (2), (3), (4), (5).

(3) Set the ratio standard at 0X00000 and the TF 2600B RANGE switch at 100 mV.

The pointer of the TF 2600B meter should be at 1.0 V and the d.v.m. should display 1-0-0-0. If necessary adjust R4 in the d.v.m. interface to obtain 1-0-0-0 V.

(4) Set the ratio standard to provide the inputs given in Table 4.2 and check that at each setting the d.v.m. display is within the limits given.

Table 4.2

Input	DVM d	lisplay
(mV)	Lower limit	Upper limit
100	0.9991	1.0009
90	0.8991	0.9009
70	0.6991	0.7009
50	0.4991	0.5009
30	0.2991	0.3009
10	0.0991	0.1009

2600-920 (1)

Page 15

Fig. 4.2 Test gear arrangement for voltage scale and a.c. output checks

4.6.5 Checking and adjusting frequency response

Test equipment : items d, e, i, j.

Then adjust R4 (d.v.m. interface) for an indication of 1-0-0-0 in the d.v.m., i.e. full-scale on TF 2600B.

(3) Perform the following checks in the order given in Table 4.3.

(1) Connect the test equipment as shown in Fig. 4.2 but without the differential voltmeter.

(2) Set the TF 2600B RANGE switch at 10 mV and the synthesizer output for 10 mV at 400 Hz.

Since some adjustments are interdependent it is advisable to repeat the checks so as to obtain the optimum adjustment.

lable 4.3
TF 2600 B range	Synthesizer output	Required d.v.m indication	Adjustment
10 mV	10 mV at 10 MHz	1-0-0-0	Adjust C38
1 V	1 V at 10 MHz	1-0-0-0	Adjust C20
100 mV	100 mV at 10 MHz	1-0-0-0	Adjust C23
10 V	5 V at 40 kHz	0-5-0-0	Adjust R6-C8
10 V	5 V at 10 MHz	0-5-0-0	Select value R2
1 mV	1 mV at 4 MHz	1-0-0-0	Select value C66
3 m V	3 mV at 8 MHz	1-0-0-0	Select value C67
300 mV	300 mV at 10 MHz	1-0-0-0	Adjust C26-C25
30 mV	30 mV at 10 MHz	1-0-0-0	Adjust C21

4.6.6 AC output voltage

Test equipment items d, e, g, i.

(1) Connect the test equipment including the differential voltmeter as shown in Fig. 4.2.

(2) Set the TF 2600B RANGE switch at 10 mV.

(3) Set the synthesizer at 400 Hz and adjust its output to obtain a display of 1-0-0-0 on the digital voltmeter.

(4) Check using the differential voltmeter that the open circuit a.c. output voltage is not less than 100 mV.

4.7 CLEANING ROTARY SWITCHES

If it is necessary to clean the contacts of the rotary RANGE switch, this should be done with benzine or white spirit (not carbon tetrachloride), and the contacts should afterwards be wiped with a suitable lubricant such as a 1% solution of petroleum jelly in white spirit. Avoid lubricants containing soap or solid materials.

Page 16

Chapter

5.1 INTRODUCTION

This chapter is intended to localize the cause of incorrect performance of the instrument and thereby effect repair. Performance limits given are for guidance only and should not be accepted as guaranteed performance specifications unless they are also quoted in the Data Summary, Sect. 1.2.

In the case of any difficulty, please write to or phone the Marconi Instruments Service Division (see address on back cover) or nearest representative, quoting the type and serial number on the data plate at the rear of the instrument. If the instrument is being returned for repair, please indicate clearly the nature of the fault or the work you require to be done.

Test equipment letter codes in the following sections refer to Table 4.1.

5.2 FAULT FINDING

Some aid to fault finding is provided by the fault tables included in each of the following sections. The tables are not extensive but they will probably be useful as directives to the cause of incorrect circuit performance.

Note. With the instrument removed from its case, signal and noise levels may, to some extent, be influenced by stray signal pick-up.

5.2.1 Circuit voltages

Test equipment : items a, d.

Voltages given on the circuit diagrams are approximate levels which can be expected using a 20 kΩ/V meter on a typical TF 2600B connected to an a.c. supply of 240 V, 50 Hz. To avoid causing oscillation, the meter should be connected through a 1 kΩ series resistor positioned at the measurement point.

5.2.2 Signal levels

Test equipment : item b.

With the RANGE switch at 1 V and with a 1 V, 400 Hz signal applied to the INPUT, signal levels at various points in the instrument should approximate those listed in Table 5.1.

Table 5.1

All voltages are r.m.s. except those marked 'p-p'

Test point	Typical signal level
TR2b	21 mV
TR3e	1.5 V
TR4b	15.1 mV
TR4c	2.3 mV
TR5c	1.3 mV
TR6c	167.2 mV
TR7c	166.7 mV
TR8b	166.7 mV
TR8e	15.0 mV
TR10e	229 mV
TR11e	12.4 mV
TR11c	2.8 V p-p (non-sinusoidal)
TR12e	2.7 V p-p (non-sinusoidal)

5.2.3 Power supply

Test equipment : item a.

Symptom : Fuse FS1 or FS2 blows when instrument is switched on.

(a) Short in a.c. input circuit or power supply circuit TR13 to TR17.

Symptom : No voltage or incorrect voltage at +30 V output.

(a) No d.c. input to regulator. Check output from bridge rectifier D14, D15, D16, D17.
(b) R92 open circuit.

Page 17

(c) C68, C71 or C72 short or partial short circuit.
(d) Suspect regulator check transistor voltages and diodes D10 and D11.
(e) Excessive current load on regulator correct load is approximately 77 mA.
Symptom : No voltage or incorrect voltage at -9 V output.
(a) D13, D18 faulty.
(b) C73 short or partial short circuit.
(c) Check R91.
(d) Excessive current load on output correct load is approximately 1.9 mA.
Symptom : 50/100 Hz ripple greater than 1.5 mV p-p at +30 V output.
(a) Faulty diode in bridge rectifier.
(b) C71 or C72 open circuit or low capacitance.
(c) Fault in regulator circuit TR13 to TR17.

Symptom : 50/100 Hz ripple greater than 20 mV p-p across D12.

(a) D18 faulty.
(b) C73 open circuit or low capacitance.

5.2.4 Voltage range check

Test equipment : item b.

Symptom: Meter pointer not as quoted in 4.6.3 (8).

(a) RANGE switch not at 10 mV or faulty.
(b) R42 requires readjustment.
(c) Low or high overall gain check signal levels as in Sect. 5.2.2. If incorrect check d.c. voltage levels and components of suspect stage.

Symptom : Digital voltmeter indication not as quoted in 4,6,3 (11).

(a) RANGE switch not at 1 mV.
(b) R71 requires readjustment.

5.2.5 Voltage scale check

Symptom : Voltage calibrations not as quoted in 4.6.4 (4).

(a) Inherent oscillation or distortion.
(b) Spurious signal pick-up.
(c) High noise level.

To check (a), (b), (c) connect an oscilloscopethrough a 10 pF probe across R66. The oscilloscope should show a closely sinusoidal waveform when the input signal is varied between 10 Hz and 10 MHz.

(d) Meter or meter circuit faulty.

Symptom : Incorrect operation on other ranges.

(a) Check interstage signal levels for appropriate attenuation.
(b) Check noise and hum levels.

5.2.6 Frequency response

Test equipment : items a, b.

Symptom : Indicated response not as quoted in Sect. 4.6.5.

(a) Incorrect interstage gain to localize, check signal levels against those listed in Table 5.1.
(b) Check d.c. voltages and components of suspect stage.

Page 18

5.2.7 AC output

Test equipment : items a, b.

Symptom : Signal level at AC OUTPUT less than 100 mV e.m.f. (using ranges above 3 mV f.s.d.).

(a) Low level signal (less than 166 mV) at input of TR9.
(b) Check interstage signal levels as in Table 5.1.
(c) Check d.c. levels and components in TR9 circuit.
(d) TR9 faulty.

5.2.8 Noise level

Test equipment : items a, b.

Symptom : Noise level greater than 25 μV with INPUT connected to 1 kΩ screened resistor.
(a) Introduced external noise.
(b) Noisy amplifier stage.
(c) Check noise level at output of each stage.
(d) Check resistors and transistors in suspect stage for noise generation.

Page 19

Replaceable parts

Introduction

The majority of the components in this instrument are located on the printed circuit board 44827-521C which has been allocated a unit identification code A1. Components not on the board have been allocated the code A0.

The complete circuit reference number for a component carries its unit code as a prefix e.g. A1C10. For convenience in the text and on the circuit diagram the prefix is not used. However, when ordering replacements or in correspondence the complete circuit reference should be quoted.

One or more of the components fitted in this instrument may differ from those listed in this chapter for any of the following reasons :

(a) Components indicated by + have their value selected during test to achieve particular performance limits.
(b) Owing to supply difficulties, components of different value or type may be substituted provided the overall performance of the instrument is maintained.
(c) As part of a policy of continuous development, components may be changed in value or type to obtain detail improvements in performance.

When there is a difference between the component fitted and the one listed, always use a replacement of the same type and value as found in the instrument.

Ordering

When ordering replacements, address the order to our Service Division (address on rear cover) or nearest agent and specify the following for each component required.

1) Type * and serial number of instrument.
(2) Complete circuit reference.
(3) Description.
(4) MI code number.
* as given on the serial number label at the rear of the instrument; if this is superseded by a model number label, quote the model number instead of the type number.

Component references

The components are listed in alpha-numerical order and the following abbreviations are used :

С	:	capacitor
Carb	:	carbon
Cer	:	ceramic
Cerm	:	cermet
D	:	semiconductor diode
Elec	:	electrolytic
FS	:	fuse
L	:	inductor
LP	:	lamp
Max	:	maximum
ME	:	meter
Met	:	metal
Min	:	minimum value
Ох	:	oxide
PL	:	plug
Plas	:	plastic dielectric
R	:	resistor
S	:	switch
SK	:	socket
Т	:	transformer
Tant	:	tantalum
TL	:	terminal
TR	:	transistor
Var	:	variable
WW	:	wirewound
+	:	value selected during test;
. 1		nominal value listed
	C Carb Cer D Elec FS L LP Max ME Met Min Ox PL Plas R S SK T Tant TL TR Var WW †	C : Carb : Cerm : D : Elec : FS : L : LP : Max : ME : Met : Met : Met : Met : Plas : R : S : SK : T : Tant : TL : TR : Var : WW :

: watts at 70 °C

Page 20

Replaceable parts

Circuit referenc	te Description	M.I. code	Circui referen	t ce Description	M.I. code
Unit	A0		R152	Met film 470Ω 2% ¹ / ₄ W	24773-265M
When or	dering, prefix circuit reference with AO		C101	Plas 100pF ±2pF 125V	26516-241N
			L10	Choke 10µH 10%	23642-5550
C100	Cer 0.1µF +50-80% 30V	26383-031S		Mounted on switch
C102	Cer 0.022µF +80-20% 250V	26383-439S		wafer SA6B
C103	Cer 0.022µF +80-20% 250V	26383-439S	L11	Choke 1.5µH 10%	23642-550Y
C104	Plas 12pF ±1pF 160V	26516-014T	L12	Choke 0.47µH 10%	23642-547Y
C105 C106	Plas 100pF ±2pF 350V Cer 0.022µF +80-20% 250V	26516-243J 26383-439S	L101	Choke	44290-600S
FS1		23411-051S	Unit	A1 (printed circuit board 44	827-521C)
FS2	100mA (time lag) 115V	23411-052W
	fuse holder	23416-191C	When or	dering, prefix circuit reference with A1
T D1			C1	Cer 0.01µF 20% 500V	26383-388H
LPI	Neon lamp 110V	23773-154G	C2	Cer 1pF ±0.25pF 750V	26329-005K
			C3	Plas 150pF 2% 125V	26516-287X
ME1	Meter	44559-014U	C4	Mica 680pF 1% 250V	26265-001H
			C5	Mica 1470pF 1% 350V	26268-363Z
PL1	Mains input connector	23423-159P	с6 †	Plas 100pF 2% 125V	26516-241B
			C7	Plas 15pF ±1pF 350V	26516-019R
R150	Met ox 150Ω 2% ¹ / ₂ W	24573-053K	C8	Var plas 2-10pF 1500V pk	26876-001F
R 151	Met film 10Ω 5% 1½W	25123-020F	С9	Cer 0.01µF -20+80% 100V	26383-055L
			C10	Plas 0.1µF 10% 100V	26582-211B
SA	Range switch	44340-128A	C11	Cer 0.01µF -20+80% 100V	26383-055L
SB	Mains on/off switch DPDT	23462-258L	C12	Plas 0.1µF 10% 100V	26582-211B
SC	Mains selector switch DPCO	23467-155G	C13	Cer 0.1µF -25+50% 30V	26383-031 Y
			C14	Cer 0.01µF -20+80% 100V	26383-055L
SK1	Receptacle BNC 50Ω	23443-443K	C15	Elec 220µF -20+100% 10V	26423-251A
SK3	Receptacle BNC 50Ω	23443-443K	C16	Cer 0.01µF -20+80% 100V	26383-055L
			C17	Elec 4.7µF -20+100% 63V	26415-801M
T1	Mains transformer	43490-012E	C18	Cer 0.1µF -25+50% 30V	26383-0315
			C19	Elec 220µF -20+100% 10V	26423-251A
TL1	Terminal	23235-176V	C20	Var Cer 2.5-6pF	26847-108B
TL2	Terminal	23235-176V	C21	Var Cer 4-20pF	26847-243C
			C22	Plas 33pF ±2pF 125V	26516-127A
X30	Bead Ferrox cube	46883 -156 T	C23	Var Cer 4-20pF	26847-243C
X31	Bead Ferrox cube	46883-156Т	C24	Plas 150pF 2% 125V	26516-287X

For symbols and abbreviations see introduction to this chapter

2600-920 (1e)

Page 21

Circuit	Description	MI code	Circuit	Description	M.I. code
reference	Description		reference	Description
C25 †	Plas 27pF ±2pF 160V	26516-108G	C60	Elec 330µF 20% 6V	26486-630W
C26	Var Cer 7-35pF	26847-120U		·
C27	Plas 680pF 2% 160V	2651 6-444 Y	C62	Elec 100µF 20% 20V	26482-326Z
C28	Plas 0.47µF 10% 63V	26582-410P	C63	Elec 330µF 20% 6V	26486-630W
C29	Plas 1.0µF 10% 63V	26582-414R	C64	Plas 1500pF 2% 125V	26516-524S
сзо †	Elec 22µF 20% 15V	26486-230B	C65	Plas 0.001µF 2% 125V	26516-481L
C31	Plas 1.5µF 10% 63V	26582-416K	C66 †	Plas 680pF 2% 160V	26516-444 Y
C32	Plas 470pF 2% 125V	26516-406H	C67 †	Plas 22pF ±2pF 125V	26516-088K
C33	Elec 1000µF -20+100% 10V	26415-824S	C68	Elec 4.7µF -20+100% 63V	26415-801M
C34	Cer 0.1µF -25+50% 30V	26383-031S	C69	Elec 47µF -20+100% 63V	26423-233V
C35	Cer 0.01µF -20+80% 100V	26383-055L	C70	Cer 0.047µF -20+50% 30V	26383-018Y
C36	Cer 0.047µF -20+50% 30V	26383-018Y	C71	Elec 220µF -20+100% 63V	26415-820J
C37	Elec 4.7µF -20+100% 63V	26415-801M	C72	Elec 220µF -20+100% 63V	26415-820J
C3 8	Var Plas 2-10pF	26876-001F	C73	Elec 220µF -20+100% 25V	26423-254E
C39	Elec 100µF -20+100% 25V	26423-243M	C74	Plas 12pF ±1pF 125V	26516-014T
C40	Cer 0.001µF -20+80% 500V	26383-242P
C41	Cer 0.047µF -20+50% 30V	26383-018Y
C42	Cer 0.1µF -20+50% 30V	26383-031S	D1	BA182	28335-677K
C43	Elec 470µF -20+100% 6.3V	26423-261L	D2	BZX79C4V7	28371-371F
C44	Elec 22µF -20+100% 40V	26423-222E	D3	BA182	28335-677K
C45	Cer 0.1µF -25+50% 30V	26383-031S	D4	BZX79C4V7	28371-371F
C46	Elec 10µF -20+100% 63V	26423-215K	D5	BZX79C10	28371-844U
C47	Plas 0.001µF 2% 125V	26516-481L	D6	BZX69C13	28372-218F
C48	Cer 0.01µF -20+80% 100V	26383-055L	D7	BZX79C10	28371-844U
C49	Elec 4.7µF -20+100% 63V	26415-801M	D 8	HP5082-2800	28349-007E
C50	Elec 1000µF -20+100% 6.3V	26423-268D	D9	HP5082-2800	28349-007E
C51	Elec 1000µF -20+100% 10V	26415-824S	D10	Z5B:29.4 Matched pair	28373-781Y
C52	Cer 0.047µF -20+50% 30V	26383-018Y	D11	Z5B:29.4	28373-781Y
C53	Cer 0.1µF -25+50% 30V	26383-031S	D12	1N4148	28336-676J
C54	Cer 0.1µF -25+50% 30V	26383-031S	D13	BZX79C9V1	28371-757P
C55	Elec 4.7µF -20+100% 63V	26415-801M	D14	1N4448	28336-246M
C56	Cer 0.001µF -20+80% 500V	26383-242P	D15	1N4448	28336-246M
C57	Elec 220µF -20+100% 10V	26423-251A	D16	1N4448	28336-246M
C58	Elec 22µF -20+100% 40V	26423-222E	D17	1N4448	28336-246M
C29	Elec 100µF -20+100% 10V	26423-240T	D18	1N4448	28336-246M

For symbols and abbreviations see introduction to this chapter

Page 22

Replaceable parts

Cir refei	cuit rence Description	M.I. code	Circu referen	nit nce	Description	M.I. cod e
L1	Choke 22µH 10%	23642-557S	R29	Met fil	lm 22Ω 2% 4 ₩	24773-233м
L2	Choke 22µH 10%	23642-557S	R30 -	† Met fil	m 4.7kΩ 2% ½W	24773-289W
L3	Choke 22µH 10%	23642-557S	R31	Met fil	m 53Ω 0.25% ¹ / ₄ W	24732-320T
			R32 -	† Met fil	m 1.5kΩ 2% ¹ / ₄ W	24773-2771
L5	Choke 22µH 10%	23642-557S	R33	Met fil	m 16.4Ω 0.25% ¹ / ₄ W	24732-397H
L6	Inductor	44290-496P	R34	Met fil:	m 68kΩ 2% 1 W	24773-317N
	•		R35	Met fil	m 82kΩ 2% 4 W	24773-319J
R1 ·	^† Met film 47kΩ 2% ¹ / ₄ W	24773-313H	R36	Met film	m 27kΩ 2% 4 W	24773-307K
R2	⁺ Met film 47Ω 2% ¹ / ₄ W	24773-241A	R37	Met filı	n 10Ω 2% 1 W	24773-338B
R3	Met film 66.5kΩ 0.5% ½W	24753-932Z	R38	Met filr	n 4.7kΩ 2% ¼W	24773-289W
R 4	Var Cerm 4.7kΩ 10% ¹ ₂ W	25711-542W	R39	Met filr	n 1kΩ 2% 1 ₩	24773-273A
R5	Met film 27.4kΩ 0.5% ¹ ₂ W	24753-914S	R40	Met film	n 150Ω 2% 4 ₩	24773-253F
R6	Var Cerm 10kΩ 10% ½W	25711-543D	R41	Met film	n 300Ω 2% 1 4W	24773-260W
R7.	Met film 10MΩ 1% 1W	24767-999K	R42	Var Cei	rm 220Ω 10% ½W	25711-546X
R8	Met film 15kΩ 2% ¹ / ₄ W	24773-301P	R43	Met filn	n 510Ω 2% 1 4W	24773-266C
R9	Met ox 150Ω 2% ¹ / ₂ W	24573-053K	R 44	Met film	n 1.2kΩ 2% 1 4W	24773-275H
R10	Met film 2.7kΩ 2% ¹ / ₄ W	24773-283L	R45	Met film	n 8.2kΩ 2% 1 4W	24773-295P
·R11	Carb 10MΩ 10% ¹ / ₂ W	24323-985J	R46	Met film	n 1.3kΩ 2% 1 4W	24773-276E
R12	Carb 10MΩ 10% ½W	24323-985J	R47	Met film	u 4.7kΩ 2% 1 4W	24773-289W
R13	Carb 2.7MΩ 5% ¼W	24312-976D	R48	Met film	3.3kΩ 2% 1 W	24773-285F
R 14	Carb 3.9MΩ 5% ¹ / ₄ W	24312-980T	R49	Met film	330Ω 2% 1 W	24773-261D
R15	Carb 4.7MΩ 5% 1 4W	24312-982X	R50	Met film	15kΩ 2% 1 W	24773-301P
R16	Met film 47Ω2% ¹ / ₄ W	24773-241A	R51	Met film	68kΩ 2% 1 /4W	24773-317N
R17	Met film 1.6kΩ 2% ¼W	24773-278Y	R52	Met film	27kΩ 2% 1 4W	24773 307K
R18	Met film 1kΩ 2% 1 W	24773-273A	R53	Met film	5.6Ω2% 1 W	241.3-219G
R19	Met film 300Ω 2% ¼W	24773-260W	R54	Met film	680Ω 2% 1 W	24773-269K
R20	Met film 560Ω 2% ¼W	24773-267R	R55	Met film	3.9kΩ 2% 1 4₩	24773-287V
R21	Met film 27kΩ 2% 4 W	24773-307K	R56	Met film	1kΩ 2% ¼ W	24773-273A
R22	Met film 1.3kΩ 2% ¼W	24773-276E	R57	Met film	39Ω 2% 4 W	24773-239Z
R23 †	Met film 4.7Ω 2% ¹ / ₄ W	24773-217J	R58	Met film	360Ω 2% ¼W	24773-262T
R24	Met film 1.6kΩ 0.25% ¹ / ₄ W	24732-399U	R59	Met film	12kΩ 2% 1 4₩	24773-299R
R25 †	Met film 22kΩ 2% ¹ / ₄ W	24773-305R	R60	Met film	56Ω 2% ¹ / ₄ W	24773-243H
R 26	Met film 510Ω 0.25% ¹ / ₄ W	24732-321P	R61	Met film	4.7Ω2% 4 W	24773-217J
R27	Met film 182Ω 0.25% ¼W	24732-398E	R62	Met film	620Ω 2% ¹ / ₄ W	24773-268B
R28	Met film 22kΩ 2% ¼W	24773-305R	R63	Met film	620Ω 2 % ‡ W	24773-268B

For symbols and abbreviations see introduction to this chapter

2600-920 (1a)

Page 23

Replaceable parts

Circuit reference	Description	M.I. code	Circuit reference	Descrij	Dtion	M.I. code
R64	Met film 4.7kΩ 2% ¹ / ₄ W	24773-289W	TR6	2N2369		28452-197H
R65	Met film 3.6kΩ 2% ¼W	24773-286G	TR7	2N2369		28452-197H
R 66	Met film 47Ω 2% ¹ / ₄ W	24773-241A	TR8	BCY71		28435-237F
R 67	Met film 5.6Ω 2% ¹ / ₄ W	24773-219G	TR9	BC109		28452-777K
R68	Met film 2.4kΩ 2% ¹ / ₄ W	24773-282N	TR10	BFY90		28452-157R
R69	Met film 4.3kΩ 2% ¼W	24773-288S	TR11	2N2369	,	28452-197H
R 70	Met film 120Ω 2% ¹ / ₄ W	24773-251L	TR12	BFY90		28452-157R
R71	Var Cerm 220Ω 10% ½W	25711-546X	TR13	BFY50		28456-777P
R72	Var Cerm 47Ω 20% ½W	25711-553B	TR14	BC107		28455-437L
R73	Met film 27Ω 2% ¼W	24773-235R	TR15	BFY50		28456-777P
R74	Met film 75Ω 2% ¼W	24773-246Y	TR16	BC107		28455-437L
R75	Met film 220Ω 2% ¹ / ₄ W	24773-257W	TR17	MM4001		28438-436V
R76	Met film 820Ω 2% ¹ / ₄ W	24773-271B
R77	Met film 5.1kΩ 2% ¼W	24773-290V	X1	•
R 78	Met film 120Ω 2% ¼W	24773-251L	to X20	Ferrite bead		46883 - 156T
R79	Met film 15kΩ 2% ¼W	24773-301P	1120
R80	Met film 2.4kΩ 2% ¼W	24773-282N		•
R 81	Met film 1kΩ 2% ¹ / ₄ W	24773-273A	Miscella	neous items	1
R 82	Met film 5.1kΩ 2% ¼W	24773-290V	Case ass	sembly :		· ·
R83	Met ox 22Ω 2% ¹ / ₂ W	24573-033J	То	p section		35900-333Z
R 84	Var Cerm 1kΩ 10% ½W	25711-544T	Во	ttom section		35623-120N
R85	Met film 1kΩ 2% ¹ / ₄ W	24773-273A	Le	ft-hand trim		34717-420H
R 86	Met film 18kΩ 2% ¹ / ₄ W	24773-303M	Ri	ght-hand trim		34717-421E
R87	Met film 300Ω 2% ¹ / ₄ W	24773-260W	Front pa	nel surround		41590-015X
R88	Met film 1kΩ 2% ¹ / ₄ W	24773-273A	Side han	dle assembly		22315-575F
R89	Met film 3.9kΩ 2% ¼W	24773-287V			Qty 2 :	22315-573L
R90	Met film 100kΩ 2% ¹ / ₄ W	24773-321L			Qty 2 :	22315-572N
R91	Met film 560Ω 2% ¹ / ₄ W	24773-267R			Qty 2 :	33900-120K
R92	WW 47Ω 5% 3W	25125-037R	Tilt stan	d		37587-925L
R9 3	Met film 820Ω 2% ‡ W	24773-271B	Tilt stan	d attachment		37588-110B
			Foot (1 c	of 2)		22315-663B
TR1	BFW11	28459-012W
TR2	BCY71	28435-237F	Knob for	SA		41145-237A
TR3	BC109	28452-777K	Cover fo	r SB		37561-103D
TR4	BCY71	28435-237F	Cover fo	r SC		37573-145C
TR5	2N2369	28452-197H	Cover fo	r fuse hold e r		37575-121B

For symbols and abbreviations see introduction to this chapter

Page 24

Circuit diagrams

Circuit notes

COMPONENT VALUES

Resistors : No suffix ohms, k kilohms, M = megohms. Capacitors : No suffix microfarads, p = picofarads. Inductors : No suffix = henrys, m = millihenrys, µ = microhenrys. + value selected during test, nominal value shown.

VOLTAGES

Shown in italics. Voltages are d.c. and relative to chassis unless otherwise indicated.

SYMBOLS

Symbols are based on the provisions of BS 3939.

+- arrow indicates clockwise rotation of knob.

tet., external front or rear panel marking.

-O- tag on printed board.

preset control.

____ Ferrite bead.

30V Source point of a supply line. 30 V

30v Source points of branches of a common supply line.

CIRCUIT REFERENCES

30 V

See introduction to Chap. 6.

SWITCHES

Rotary switches are drawn schematically. Letters or figures indicate control knob settings. 1F = 1st section (nearest front panel), front. 1B = 1st section, back. 2F = 2nd section, front. etc.

Page 25

2600-920 (1e)

Page 26

Page 27

2600-920 (1e)

Page 28

21.

Marconi TF 2600B Service and user manual

Video Voltmeter TF 2600B

RADIO FREQUENCY INTERFERENCE

Contents

Chapter 1 GENERAL INFORMATION

Chapter 2 OPERATION

Chapter 3 TECHNICAL DESCRIPTION

Chapter 4 MAINTENANCE

Chapter 5 REPAIR

Chapter 6 REPLACEABLE PARTS

Chapter 7 CIRCUIT DIAGRAMS

General information

1.1 INTRODUCTION

1.2 DATA SUMMARY

METER

INPUT

1.3 ACCESSORIES SUPPLIED

Operation

2.1 PRELIMINARY REQUIREMENTS

2.2 AC SUPPLY CABLE

2.3 FUSES

2.4 CONTROLS AND CONNECTORS

Front panel

Rear panel

2.5 VOLTAGE MEASUREMENTS

2.5.1 Sinusoidal waveforms

2.5.2 Noise levels

2.5.3 Non-sinusoidal waveforms

2.5.4 Determination of dBm

Table 2.2

2.6 POWER MEASUREMENTS

2.7 USING TF 2600B AS AN AMPLIFIER

2.8 DC OUTPUT

2.9 INPUT AND OUTPUT CONNECTORS

Technical description

3.1 MECHANICAL CHARACTERISTICS

3.2 CIRCUIT SUMMARY

3.3 CIRCUIT FUNCTIONS

3.3.1 Input attenuator

3.3.2 Overload protection circuit Circuit diagram Fig. 7.1

3.3.3 First amplifier

3.3.4 Inter-amplifier attenuator

3.3.5 Second amplifier

3.3.6 Final amplifier and diode bridge rectifier

3.3.7 Power supply

Maintenance

4.1 INTRODUCTION

4.2 SCREW FASTENERS

4.3 ACCESS TO SUB-ASSEMBLIES AND COMPONENTS

4.4 PRELIMINARY CHECKS

4.5 TEST EQUIPMENT

4.6 PERFORMANCE CHECKS

4.6.1 Power supply

4.6.2 Noise check

4.6.3 Voltage range check

4.6.4 Voltage scale check

4.6.5 Checking and adjusting frequency response

4.6.6 AC output voltage

4.7 CLEANING ROTARY SWITCHES

5.1 INTRODUCTION

5.2 FAULT FINDING

5.2.1 Circuit voltages

5.2.2 Signal levels

Table 5.1

5.2.3 Power supply

5.2.4 Voltage range check

5.2.5 Voltage scale check

5.2.6 Frequency response

5.2.7 AC output

5.2.8 Noise level

Replaceable parts

Introduction

Ordering

Component references

Replaceable parts

Replaceable parts

Replaceable parts

Circuit diagrams

Circuit notes

VOLTAGES