Leisure Craft P-300 Service manual

Index & Warnings

Technical Specifications, Test Procedures & Adjustments

Wiring Connections

Inputs & Protections, Power Supply and Display Boards

Power Amplifier Board

Part List, Layout

2
4
5
6
7

SERVICE MANUAL

Schematic Diagrams

CODE : 277318

GENERALMUSIC S.p.A. Sales Division: 47842 S.Giovanni in Marignano (RN) ITALY - Via delle Rose, 12 - tel. [phone] - tlx 550555 GMUSIC I - fax [phone]

Notice

Service must be carried out by qualified personnel only. Any tampering carried out by unqualified personnel during the guarantee

For a correct operation of the instrument, after having switched off, be careful to wait at least 3 seconds before switching on again.
To improve the device's specifications, the schematic diagrams may be subject to change without prior notice.

period will forfeit the right to guarantee.

Schematic Notes

All components marked by this symbol have special safety characteristics, when replacing any of these components use only
manufacturer's specified parts.

The (µ) micro symbol of capacitance value is substituted by U. The (Ω) omega symbol of resistance value is substituted by E.
The electrolytic capacitors are 25Vdc rated voltage unless otherwise specified. All resistors are 1/4W unless otherwise specified.

Soldering point.
Male connector.
Female connector.
M/F faston connector.
Test point.
Flag joined with one or more flags with the same signal name inscribed.

Supply voltage.
Logic supply ground.
Analog supply ground.
Signal ground.
Chassis ground.

Observe precautions when handling

ATTENTION

electrostatic sensitive devices

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TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS

TECHNICAL SPECIFICATIONS

TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS

Dimensions: (WxHxD) 483x44x310mm (1U)
Weight: 8Kg

➭ Before proceed to supply the amplifier check visually the internal assem-

bly, if appears an evident damage find the most possible reasons that
cause it.

➭ Check the wiring cables for possible interruptions or shorts.

CN3 pin 7-9-10 =-15±1Vdc

➭ If one or more voltages don’t correspond, check the rectifiers, capacitors

and transformers disconnecting them from circuitry, refer to schematics.

Power Requirements: (230Vac±10% 50Hz) 300VA
Output Power: (8Ω stereo/parallel) 2x 150Watts
Max. Undistorted Out: (8Ω stereo/parallel) 98Vpp
Input Sensitivity: (constant sensitivity) 0.775Vrms (0dB)

(constant gain) 1.75Vrms (+7dB)

Input Impedance: (balanced) 30KΩ

(unbalanced) 15KΩ

Voltage Gain: (constant sensitivity) 33±0.5dB

(constant gain) 26±0.5dB

Slew Rate: 25V/µS
Damping Factor: (8Ω stereo/parallel) >400
Frequency Response (-0.2dB) 20Hz÷20KHz
at Full Power: (-3dB) 10Hz÷60KHz
IMD: (SMPTE 60Hz/7KHz 4:1) <0.1%
THD: (THD+N) <0.1%
S/N Ratio: (unweighted) >95dB
Crosstalk: (1KHz) >70dB

➭ If the damage has burnt a printed circuit board don’t try to repair it,

replace with a new one.

Test InstrumentsTest Instruments

Test Instruments

Test InstrumentsTest Instruments

➭ Audio Generator
➭ Dual Trace Oscilloscope
➭ Digital Multimeter
➭ 4Ω 500W, 8Ω 300W, 100Ω 10W resistors
➭ Variac (0÷250Vac)

SetupSetup

Setup

SetupSetup

➭ Connect the Variac between the mains and the amplifier and set it at zero

voltage.

➭ Set the amplifier in STEREO MODE and turn full clockwise the LEVEL

potentiometers.

➭ Connect the audio generator to the channel inputs and set it to 1KHz

775mV

➭ The procedures that follow must be executed subsequently in the order

specified.

(0dB) sinusoidal signal.

RMS

Channels CheckChannels Check

Channels Check

Channels CheckChannels Check

➭ The channel A is on the right and channel B is on the left of the chassis.
➭ These procedures are intended for one channel at a time, repeat these

operation for the other channel.

➭ Verify, with the Multimeter, the insulation between the heatsink and the

transistors collectors.

➭ Verify, with the Multimeter, the PTC resistor value (R33 connected across

pin 8 an pin 9 of CN3), it must be between 50Ω and 200Ω.
SETUP:SETUP:

➭

SETUP:

SETUP:SETUP:
Connect the CH1 scope GND clip to CN2 pin 1 (GND terminal).
Connect the CH1 probe tip to CN2 pin 2 (AMP output).
Connect the CH2 probe tip to D9 anode and set it sensitivity at 5V/div.
Set the LEVEL potentiometers full clockwise.
The load resistor is disconnected.

INITIAL TEST:INITIAL TEST:

➭

INITIAL TEST:

INITIAL TEST:INITIAL TEST:
Increase slowly the Variac. The channel output signals must be symmetri­cal respect the GND without visible distortion and oscillation as shown in

Fig.1 Trace A (Trace B

distortion read the section ADVICES and proceed to check the other
channel.

Fig. 1Fig. 1

Fig. 1

Fig. 1Fig. 1

shown the amplifier 2nd stage input). If there is a

Trace A (20V/div.)

TEST PROCEDURES & ADJUSTMENTSTEST PROCEDURES & ADJUSTMENTS

TEST PROCEDURES & ADJUSTMENTS

TEST PROCEDURES & ADJUSTMENTSTEST PROCEDURES & ADJUSTMENTS

PrecautionPrecaution

Precaution

PrecautionPrecaution

➭ To prevent short circuit during any test,

EARTH insulatedEARTH insulated

EARTH insulated, this occurs because some test require to connect its

EARTH insulatedEARTH insulated
probe to the amplifier output, non-compliance may cause damages to
oscilloscope inputs circuitry.

➭ Before removing or installing any modules and connectors,

the amplifier from AC MAINSthe amplifier from AC MAINS

the amplifier from AC MAINS and measure the DC supply voltages

the amplifier from AC MAINSthe amplifier from AC MAINS
across each of the power suppliy capacitors. If your measurement on any
of the caps is greater than 10Vdc, connect a 100Ω 10W resistor across
the applicable caps to discharge them for your safety. Remember to
remove the discharge resistor immediately after discharging caps.
power up the amplifier with the discharge resistor connectedpower up the amplifier with the discharge resistor connected

power up the amplifier with the discharge resistor connected.

power up the amplifier with the discharge resistor connectedpower up the amplifier with the discharge resistor connected

➭ Read these notes entirely before proceeding to any operation. These

notes are not comprehensive of all damages that possibly occur, but
includes some specifically advices, checks and adjustments relative to
this amplifier.

RemarksRemarks

Remarks

RemarksRemarks

➭ The power supply utilizes a dual bipolar DC rail configuration with low and

high voltages; one positive and one negative low rail (+/-Vcc1) and one
positive and one negative high rail (+/-Vcc2).

Visual CheckVisual Check

Visual Check

Visual CheckVisual Check

➭ Use compressed air to clear dust in the amplifier chassis.

the oscilloscope must bethe oscilloscope must be

the oscilloscope must be

the oscilloscope must bethe oscilloscope must be

disconnectdisconnect

disconnect

disconnectdisconnect

Do notDo not

Do not

Do notDo not

Supply CheckSupply Check

Supply Check

Supply CheckSupply Check

➭ Remove the transformer secondary fuses (located on SUPPLY & PRO-

TECTIONS board), set the Variac to the nominal mains voltage, check
with the Multimeter the AC supply voltages:

F1-F2=52±1.5Vac
F3-F4=88±3Vac.

➭ Re-set the Variac at zero voltage, turn off the amplifier and put the fuses

back on its holders.

➭ Connect the oscilloscope probes CH1/2 to the channel outputs, before

RL1, set both to 20V/div. 200µS/div.

➭ Set up the Variac slowly monitoring the Outputs with the oscilloscope

CH1/2 connected, it should display the sinusoidal input signal amplified
with no distortions, if a distortion occur check the POWER AMPLIFIER
boards as suggested in the ADVICES section.

➭ If the protection trips, turn off the amplifier, wait some minutes and

disconnect the supplies from the outputs modules (CN1, CN4 on POWER
AMPLIFIER boards), continue to check the supplies.

CAUTION: Before re-connecting the output modules to the supplies,CAUTION: Before re-connecting the output modules to the supplies,

➭

CAUTION: Before re-connecting the output modules to the supplies,

CAUTION: Before re-connecting the output modules to the supplies,CAUTION: Before re-connecting the output modules to the supplies,
you must have the capacitors discharged for your safety: connect ayou must have the capacitors discharged for your safety: connect a

you must have the capacitors discharged for your safety: connect a

you must have the capacitors discharged for your safety: connect ayou must have the capacitors discharged for your safety: connect a
100100

ΩΩ

10W resistor across the caps and remove the resistor just after 10W resistor across the caps and remove the resistor just after

100

Ω

10W resistor across the caps and remove the resistor just after

100100

ΩΩ

10W resistor across the caps and remove the resistor just after 10W resistor across the caps and remove the resistor just after

they are discharged.they are discharged.

they are discharged.

they are discharged.they are discharged.

➭ Finally verify the DC supplies on POWER SUPPLIES board:

CN1 pin 1-2 (+Vcc2) =+61±2Vdc
CN1 pin 3-4 (+Vcc1) =+36±1.5Vdc
CN2 pin 1-2 (-Vcc1) =-36±1.5Vdc
CN2 pin 3-4 (-Vcc2) =-61±2Vdc
CN3 pin 3-4-5 =+15±1Vdc

Trace B (5V/div.)

BIAS ADJUSTMENT:BIAS ADJUSTMENT:

➭

BIAS ADJUSTMENT:

BIAS ADJUSTMENT:BIAS ADJUSTMENT:
Set the generator level at zero, connect the Multimeter across
and collector of TR8, then adjust R32 trimmer to read 2.5Vdc.
Set the CH2 scope sensitivity at 0.1V/div. and adjust the R35 trimmer to
set the CH2 trace at the centre of the scope screen.

HIGH RAIL CHECK:HIGH RAIL CHECK:

➭

HIGH RAIL CHECK:

HIGH RAIL CHECK:HIGH RAIL CHECK:
Connect the CH2 probe tip to D3 cathode and set it sensitivity at 20V/div.
When the output signal (Positive half-wave) is less than 30Vp the voltage
on D3 cathode must remain constant at 36V, when the output signal
exceeds 30Vp the voltage must follow the output signal with 6V offset
(see

Fig.2 Trace B

D14 anode (see
Connect the 8Ω 300W load on the output and repeat the INITIAL and
HIGH RAIL checks.
Check the signal clipping, it must occur at 48±2Vpp (see

A,B,C

).

SIGNAL/CLIP SENSOR CHECK:SIGNAL/CLIP SENSOR CHECK:

➭

SIGNAL/CLIP SENSOR CHECK:

SIGNAL/CLIP SENSOR CHECK:SIGNAL/CLIP SENSOR CHECK:
Set the LEVEL pot to minimum, set the scope timebase at 1V/div. 200µS/
div., then increase the level and check the SIGNAL/CLIP led activity: it
must turn on (green light) when the amplifier output is higher than 1Vp.
Set the scope at 20V/div. and increase the level, check the led: it must

), to check the negative high rail connect the probe to

Fig.2 Trace C

).

the emitter

Fig.3 Trace

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22

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22

Fig. 2Fig. 2

Fig. 2

Fig. 2Fig. 2

Trace B (20V/div.)

Trace A (20V/div.)

Trace C (20V/div.)

Fig. 3Fig. 3

Fig. 3

Fig. 3Fig. 3

Trace B (20V/div.)

Trace A (20V/div.)

Trace C (20V/div.)

change from green to red colour at the amplifier output signal clipping.
CURRENT AND SHORT CIRCUIT SENSOR CHECK:CURRENT AND SHORT CIRCUIT SENSOR CHECK:

➭

CURRENT AND SHORT CIRCUIT SENSOR CHECK:

CURRENT AND SHORT CIRCUIT SENSOR CHECK:CURRENT AND SHORT CIRCUIT SENSOR CHECK:
Set both the scope channels sensitivity to 0.5V/div., connect the scope
CH1 GND clip at CN3 pin 2 (AMP output) and the probe tip at TR6 (NPN)
emitter, connect the CH2 probe tip at TR13 (PNP) emitter.
Set the generator to have approx. 1Vp on the emitters: their difference
must be less than 0.2V on the peaks (see

Fig.4 Trace A & B

).

Connect a 4Ω 500W load. Increase the input signal, the output current

Fig. 4Fig. 4

Fig. 4

Fig. 4Fig. 4

Trace A (0.5V/div.)

fier, connect temporarily (by means of a suitable conductor wire) CN2 pin
2 to +15Vdc (CN3 pin 5), the PROTECT led must turn on in 5 seconds
approx.
Remove the connection, wait until the leds turn off and after some sec­onds repeat the check with -15Vdc (available on CN3 pin 3), the led
PROTECT must turn on again.

BIAS CHECK:BIAS CHECK:

➭

BIAS CHECK:

BIAS CHECK:BIAS CHECK:
Disconnect CH2 probe. Connect the CH1 scope GND clip to CN2 pin 1
(GND terminal) and its probe tip to CN2 pin 2 (AMP output). Adjust the
generator level until the sinewave appears at full screen amplitude, no
crossover distortion must be detectable: if necessary re-adjust R32.
BANDWIDTH CHECK:BANDWIDTH CHECK:

➭

BANDWIDTH CHECK:

BANDWIDTH CHECK:BANDWIDTH CHECK:
Set CH1 scope sensitivity at 20V/div., increase the generator level to
have 80Vpp, sweep the generator frequency from 20Hz to 20KHz: the
output level must have not detectable level changes.

SLEW RATE CHECK:SLEW RATE CHECK:

➭

SLEW RATE CHECK:

SLEW RATE CHECK:SLEW RATE CHECK:
Set the scope sensitivity to 10V/div. 1µS/div. and set the generator to
1KHz square wave mode. Check the output square wave rising and falling

Fig. 6Fig. 6

Fig. 6

Fig. 6Fig. 6

Trace A (10V/div.)

edge slopes: both must be 10V/µS or more as shown in

Inputs & Protections Board CheckInputs & Protections Board Check

Inputs & Protections Board Check

Inputs & Protections Board CheckInputs & Protections Board Check

Fig 6

.

AMPLIFIER GAIN CHECKAMPLIFIER GAIN CHECK

➭

AMPLIFIER GAIN CHECK

AMPLIFIER GAIN CHECKAMPLIFIER GAIN CHECK
Set CH2 scope at 20V/div. and connect it to the amplifier output of the
channel under test. By means of the SENSITIVITY switch check the
output levels: at 775mV position the output voltage must be 50±1.5Vp
and at 1.75V position must be 22.5±0.5Vp.
SIGNAL TO NOISE RATIO CHECKSIGNAL TO NOISE RATIO CHECK

➭

SIGNAL TO NOISE RATIO CHECK

SIGNAL TO NOISE RATIO CHECKSIGNAL TO NOISE RATIO CHECK
Disconnect the audio generator and short the input (pin 1,2,3 of XLR
socket shorted) the output signal (noise) must be less 1mV.

AdvicesAdvices

Advices

AdvicesAdvices

➭ Check the channels one at time to determine which is right (note: if you

have a spare amplifier module that you know as right, use it).

➭ If you have determinate that the problem is a short on a rail, you must

check the output transistors.
To determine which transistor devices are bad, use a soldering iron to lift
one leg of each emitter pin and measure the emitter-collector resistance
on each device. Unsolder and lift one leg of each base pin and check the
base-collector resistance of each transistor and replace any that measure
as a short.
If all the transistors are OK, unsolder and lift one leg of each diode and
check them.
Check the circuit board for open foil traces.
Use the Multimeter as Ohm-meter to check the resistors, particularly the
base and emitter resistors of damaged transistor.

➭ If the input sinewave appears to be distorted during the negative cycle,

you can assume that the problem is located somewhere in the circuitry of
the positive low rail.
If the positive cycle appears distorted, you can assume that the problem
is in the circuitry of the negative low rail.

➭ If the high rails appear distorted or are not modulating as shown in figure,

then the problem probably exists somewhere in the circuitry of the re­spective (+ or -) defective high rail. Refer to the schematics.

Trace B (0.5V/div.)

limiter must keep the emitter voltages, both half channel, at 1.5Vp
approx. (see

Fig.5 Trace A

).
Temporarily short the amplifier output: the current limiter must keep the
emitter voltages (both half channel) at 1 approx. (see

Fig. 5Fig. 5

Fig. 5

Fig. 5Fig. 5

OFFSET SENSOR CHECK:OFFSET SENSOR CHECK:

➭

OFFSET SENSOR CHECK:

OFFSET SENSOR CHECK:OFFSET SENSOR CHECK:

Fig.5 Trace B

Trace A (0.5V/div.)

Trace B (0.5V/div.)

Set the Variac to zero voltage output, disconnect the amplifier load and
the supply connection to the Power board (CN1,2,4), turn on the ampli-

➭ These procedures are intended for one channel at a time, repeat these

operations for the other channel.
SETUP:SETUP:

➭

SETUP:

SETUP:SETUP:
Connect the CH1 probe to amplifier input of the channel under test and
set both at 500mV/div. 200mS/div.
Connect the CH2 probe to amplifier output of the channel under test and
set it at 10mV/div. 200mS/div.
Set the audio generator at 1KHz sinus. 775mV

RMS

(0dB).

Set the LEVEL potentiometers full clockwise.

).

The load resistor is disconnected.

CMRR ADJUSTMENTCMRR ADJUSTMENT

➭

CMRR ADJUSTMENT

CMRR ADJUSTMENTCMRR ADJUSTMENT
Temporarily disconnect pin 3 from pin 1 and short the pin 2 (positive
input) and pin 3 (negative input) of XLR input socket.
Adjust the trimmer R6 (channel A) or R19 (channel B) to obtain the
minimum output level.
GAIN ADJUSTMENTGAIN ADJUSTMENT

➭

GAIN ADJUSTMENT

GAIN ADJUSTMENTGAIN ADJUSTMENT
Re-set the input signal at pin 2 (positive input) and pin 3 (negative input)
short with pin 1 (GND) of XLR input socket.
Set CH2 scope at 500mV/div. and connect it to the output of INPUTS &
PROTECTIONS board (CN4 pin 10 for channel A or CN4 pin 12 for
channel B).
Set the input SENSITIVITY (SW1) at 1.75Vrms, adjust the trimmer R9
(channel. A) or R17 (channel B) to obtain the same amplitude of the
scope signals.

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