Sencore TC28 Service Manual
TC28
"
THE HYBRIDER
SERVICE
"
MANUAL
SAFETY REMINDERS
When testing electronic equipment, there is always a danger present.
Unexpected high voltages can be present at unusual locations in defective
equipment. The technician should become familiar with the device that
he is working on and observe the following precautions.
2.
3.
4.
5.
1.
When making test lead connections to high voltage points, remove
the power. If this cannot be done, be sure to avoid contact with
other equipment or metal objects. Place one hand in your pocket
as a safety precaution and stand on an insulated floor to reduce
the possibility of shock.
Discharge filter capacitors before connecting test leads to them.
Capacitors can store a charge that could be dangerous to the tech-
nician.
Be sure your equipment is in good order. Broken or frayed test
leads can be extremely dangerous and can expose the technician
to dangerous potentials.
Remove the test leads immediately after the test has been completed
to reduce the possibility of shock.
Do not work alone when working on hazardous circuits. Always
have another person close by in case of accident. Remember, even
a minor shock can be the cause of a more serious accident,
falling against the equipment, or coming in contact with
voltages.
such as
high
1
TABLE OF CONTENTS
SAFETY REMINDERS
INTRODUCTION
DESCRIPTION
FEATURES
SPECIFICATIONS
CONTROLS
GENERAL OPERATIONS
OPERATION
TUBE TEST SET UP
SHORTS TEST
EMISSION TEST
GRID - LEAKAGE TEST
LIFE TEST
FILAMENT WARM UP TIME
FILAMENT VOLTAGE SENSITIVITY
REJUVENATION
SET UP FOR NEW TUBES .
"A" PIN ELIMINATION
"B" FILAMENT .
"C" LOAD
"D" SET UP
SOCKET SET UP
EXAMPLE OF SETTING UP THE TC28 FOR NEW TUBES
TRANSISTOR TESTS
GAIN TEST
LEAKAGE TEST
DETERMINING BASING
LOCATING LEAKAGE
CHECKING DIODES .
CIRCUIT DESCRIPTION
THEORY OF OPERATION - TUBE TEST'
EMISSION TEST
GRID - LEAKAGE TEST
SHORTS TEST
THEORY OF OPERATION - TRANSISTOR TEST
GAIN TEST
POWER SUPPLY
2KHz OSCILLATOR AND SIGNAL AMPLIFIERS
LOGIC CIRCUIT AND INDICATOR DRIVE
LEAKAGE TEST
SERVICING
DISSASSEMBLY INSTRUCTIONS
CALIBRATION
TROUBLE CHARTS . .
SERVICE AND WARRANTY
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INTRODUCTION
DESCRIPTION
Numerous solid-state devices are finding increasing application in tele-
vision and other home entertainment equipment. These devices are also
being used in conjunction with a multitude of tube types to produce the
hybrid sets.
To be effective in the field service of these units, the service technician is
faced with transporting a rather cumbersome and costly array of test
equipment. The Sencore engineering staff is aware of the problems and
needs encountered in the service industry. In response to these needs, the
ever popular Mighty Mite Tube tester has been expanded to incorporate
the features of Sencore's latest solid state device tester, the
TONE CRICKET. Now, in one compact, rugged, easy-to-use unit, exists
the ability to completely and reliably test the tubes, transistors, FET's
and diode devices found in modern home entertainment equipment.
FEATURES
TOUCH
*
A single instrument for fast, accurate testing of tubes, transistors and
FET's without complicated set ups.
*
Pin elimination switches for greater capability in tube tests as
types are announced.
*
Full cathode current emission test of tubes.
Sensitive 100 megohm grid leakage test in addition to regular shorts
*
test, all on a large easy-to-read meter.
Complete test for transistors and FET's including in-circuit gain
*
out-of-circuit gain and leakage with NO set-up or basing data required.
Rugged construction throughout, including protection against overload
*
for sensitive meter and circuitry.
SPECIFICATIONS
DEVICES TESTED
new
and
Devices tested
TUBE TESTS:
Emission
Tubes, transistors, diodes, single-gate FET's
Load currents to 120mA and maximum applied
voltage of 40 VAC RMS
3
Grid-Leakage
100 Megohm or less reads BAD. 100 Megohms to
200 Megohms reads in questionable area.
Shorts 200,000 ohms or less (40 VAC RMS applied voltage)
indicates short on meter.
TRANSISTOR TESTS:
Gain (IN or
OUT of
Circuit)
VCE = 5 volts; VBE = 3 volts peak-to-peak, zero
reference, 2KHz frequency.
indication
plus audible "chirp" for good test
GOOD/BAD meter
indication.
Leakage (OUT
of circuit only)
5VDC applied voltage, meter indicates 0 - 3000
microamps leakage current.
CONTROLS
GENERAL OPERATION
TUBES/TRANSISTORS FUNCTION SWITCH:
applies power to the TC28, selects tube or transistor tests and the type
test to be made.
This rotary switch
METER ZERO: This control is used to set meter to zero previous to
making any test.
CONTROLS RELATED TO TUBE TEST:
"
"A
SWITCHES: These slide switches switched to the down position
serve to isolate extra connections to the tube which would falsely indicate
a shorted condition. The slide switch labeled RESET instantly clears all
pin elimination switches.
FILAMENT or "B" SWITCH: This rotary switch sets the proper fila-
ment voltage for the tube being tested.
LOAD or "C" SWITCH: This rotary switch determines the range of
load current to be carried by the tube during the emission test.
4
Fig. 1
TC28 "The Hybrider"
5
SETUP or "D" SWITCH: This rotary switch selects the control grid pin
for the emission test. It also serves as the shorts test switch, for any inter-
electrode shorts, by rotating the switch through its positions.
LIFE TEST: This slide switch provides a test of the useable life of a
tube by measuring how well the tube performs with a reduced filament
voltage.
CONTROLS RELATED TO TRANSISTOR TEST:
TEST SWITCHES: These six pushbutton switches apply the test voltage
to the elements of the device under test, and mechanically rotate lead
connection to all possible basing configurations, thus eliminating
requirements for basing or circuit information.
CONNECTIONS: A socket panel provides a total of 13 tube sockets
plus 1 transistor socket for all test conditions. A test lead cable terminat-
ed in
3
EZ Hook connectors facilitates in-circuit transistor or FET gain
and leakage tests.
OPERATION
TUBE TEST SET UP
Operation of the TC28 Hybrider has been designed for simplicity, speed
and accuracy.
follow the basic test procedure outlined below.
Connect the TC28 Hybrider to a grounded source of 105 to 125
1.
volts, 50 to 60 Hz, AC power.
2.
Locate the tube type to be tested in the setup chart. Looking to the
right of the tube number, observe the setup information for the
controls labeled A,B,C,D and socket. Some tubes have more than
one listing indicating that the tube has more than one section to be
tested.
3.
Push the PIN ELIMINATION switches listed under A down
inate those pins. If none are listed, leave all switches in the up
position.
4.
Set the B,C, and D switches to the positions indicated and insert the
tube into the socket listed.
make the emission and grid leakage test on each section. The shorts
test need be made only once.
All that is necessary to completely check a tube is to
Each section of the multiple tube is tested separately.
Where more than one setting is listed,
to elim-
;
SHORTS TEST
Set the TUBES/TRANSISTOR Function Switch to SHORTS and check
the front panel METER ZERO adjust to ensure a "0" indication on the
meter.
rotate the "D
Allow a period of time for the tube filament to warm up, then
"
switch slowly through all of its positions while observing
6
the meter. If no short exists or the resistance of the short is greater than
200,000 ohms, the meter will remain in the GOOD area of the GOOD/
BAD SHORTS scale. Shorts of 200,000 ohms or less will be indicated to
a relative degree on the SHORTS scale. Tubes having a directly heated
cathode (those in which the filament serves as the cathode) will show a
direct short between heater and cathode on the H-K position of the "D"
Switch.
setup book by an asterisk (*) .
This is a normal condition and these tubes are indicated in the
EMISSION TEST
If the tube passes the SHORTS test, rotate the Function switch to the
EMISSION position and read the emission quality of the tube on the top
scale of the meter. A tube indicating in the questionable area (?), has
an emission level much lower than normal. It's replacement would be
determined by you and your customer, based on the nature of the circuit
in which the tube is to operate.
GRID-LEAKAGE TEST
If the tube reads in the GOOD area of the meter and passes the EMISSION
test, switch to GRID LEAKAGE and read the grid leakage of the tube on
the GRID LEAKAGE scale of the meter. This is a very important check
and will pinpoint troublesome tubes that may otherwise check good. If
the meter is indicating in the GOOD area of the scale but slowly rising,
wait a minute or so to allow the meter to stabilize before judging test
results.
make a grid leakage check after an extended emission check. If the tube
is left in the emission check position for several minutes, the grid will
heat up and, when switched to grid leakage, will read higher than normal.
Allow the tube to cool slightly before the grid leakage check. You can
expedite the grid leakage check by raising the filament voltage for a few
seconds.
check, but will show up grid leakage. If the grid leakage indication climbs
into the BAD area on the meter, reduce the filament voltage and see if the
meter remains in the bad area. If it does so, then the tube will give
trouble in the circuit and should be replaced. If the meter drops off
rapidly back into the GOOD area, then the tube is good.
On large power tubes, such as a horizontal output tube, do not
This is not the same overheating as was caused in the emission
If the tube passes all of the above tests, it can be considered good and
need not be replaced. If the tube is in the questionable area on any test,
it becomes a value judgement based upon circumstances as to whether or
not it should be replaced.
LIFE TEST
If the meter needle climbs very slowly into the GOOD area or Questionable
area of the meter on the Emission test, the life expectancy of the tube
can be considered much less than if the meter indicated
7
GOOD
in
a
shorter period of time. Also, if the needle should climb into the GOOD
area and then "fall off," life expectancy can be considered much less.
A general measure of the usable life remaining in a tube can be obtained
by using the "Life test" position of the TC28 "Hybrider." Simply slide
the LIFE TEST switch to the right and hold it for a few moments. Observe
the emission level of the tube during this time. If the emission remains
the same or drops only slightly the tube can be considered good. If the
emission falls off quickly into the questionable or bad areas, it may be
wise to replace the tube. (The rapid drop in emission generally indicates a
short life expectancy).
FILAMENT WARM UP TIME
When replacing a costly horizontal output tube in a television receiver, it
is
a good idea to not only check the horizontal oscillator for emission
and other standard tests, but to also check the length of time it takes to
warm up. If the horizontal oscillator tube is slower in warming up than
the output tube, the output tube will draw heavy current and its life will
be shortened considerably. Checking the warm up time of the oscillator
tube and making sure that it is as fast or faster than the output tube can
reduce the chance of a call back later for the same trouble and keep your
customer's confidence high in your service ability.
FILAMENT VOLTAGE SENSITIVITY
Some tubes may check good on the emission test and pass the other tests
in the Hybrider, but still not operate properly in the receiver. These tubes
may have a filament sensitive cathode.
from the tube will change with a change in the applied filament voltage to
the tube.
transformer in the receiver. This type of tube can be most troublesome
in series string receivers.
TEST switch while monitoring the emission of the tube on the meter. A
good tube will not change its reading at all while a filament sensitive tube
will drop in emission. If the tube falls into the questionable area (?) on
the meter, it will give trouble in the circuit and should be replaced.
This is caused from a low power line or defective power
To test for this trouble, simply push the LIFE
This means that the emission
REJUVENATION
If you wish to rejuvenate a small tube, merely increase the filament
voltage by setting switch "B" one setting higher for ten to fifteen
seconds.
material from under the oxide coating.
measure as rejuvenation of a receiving tube will not last very long.
This will super heat the cathode and boil out more emitting
This is only a temporary
8
SET UP FOR NEW TUBES
New tubes can sometimes be a problem as they
set-up chart. This can be especially true on new receivers just introduced
by the set manufacturers. Though new tubes are seldom
the present time, new tubes will undoubtedly
an
understanding of the setup controls and what
the Hybrider from a tube manual or even the schematic
itself.
"A"
The "A" PIN ELIMINATION switch is used to isolate internal connections
of two pins to the same element of the tube so that a test
For example, the tube basing shown in Figure 2 is a
trol grid is tied to pins 2 and 6, the screen grid to pins 1 and 7 and pin 9 is
an internal connection that could be
tube.
shorts in the tube, the PIN ELIMINATION switches 6, 7, and
set in the down position to open these pins before the test is made. All the
numbers correspond to the tube base pin number except for socket
number 10, the compactron, where pin 11 is connected to PIN
ELIMINATION switch number 1. If no isolation is
should be in the uppermost position. After
RESET switch to the right to place all switches in the
can be moved independently of each other, either up
RESET switch.
PIN ELIMINATION
connected to any pin inside of the
To eliminate any shorts indication other than that which
may not be listed in the
being added at
appear in the future. With
each does, you can set
of the receiver
may be made.
9QL basing. The con-
are true
9 would be
needed, all switches
each
tube
is tested, push the
up position. Each
or down or set with
"B"
This switch selects the filament voltage applied to the
from 1 volt to over 50 volts. The twelve position switch selects
voltage range and, with the unique design of the
FILAMENT
filament transformer,
9
tube under test
a
the tube under test will load the transformer to obtain the correct voltage for testing.
FILAMENT switch to the correct voltage or voltage range.
When setting up a new tube, simply set the "B"
"C"
This switch selects the proper AC voltage to be applied to the plate of the
tube as well as the correct load resistor so that the tube's designed current
can be set and the tube checked under full load. The current ranges for
the settings of the "C" LOAD switch are as follows:
LOAD switch
A
B
C
D
E
The current that the "C" LOAD switch is set to is the normal cathode
current under normal bias conditions as listed in the tube manual. If a
tube manual is not handy, compute the cathode current by the voltage
drop
schematic by using Ohm's Law.
LOAD
Cathode Current
50mA plus
20 - 50mA
15 - 30mA
10 -16mA
6 - 12mA
across the cathode or plate load resistor in the circuit or from the
LOAD switch
F 2 - 7mA
G
H
J
Cathode Current
.7 - 2mA
.5 - .8m A
.5mA or less
"D"
The "D" switch is used to pick up the control grid for the test on the
tube. It was discovered many years ago that approximately 97% of the
electrons would go to the control grid when checking cathode emission.
This is now used as the pick-up element. In the example of Figure 2, the
"D" switch would be set to one of the control grids that is not isolated.
If pin 6 were to be isolated, the "D" switch would be set to pick up pin
2.
The only exception to the above is on socket number 10 where pin 11 on
the tube base is picked up with the first position of the "D" switch.
Sockets number 3 and 8 are wired identically except that socket number
8 has three pins not connected. This socket is used to isolate extra
connections where more than two base pins are connected to the same
element such as in the 1X2 high voltage rectifier. The seven-pin sockets
4 and 7 are alike except that the filament pins on socket 4 are 3 and 4
while on socket 7 they are 1 and 7.
SET
UP
SOCKET SET UP
The sockets on the TC28 have the filament pins prewired to eliminate the
extra setup that is involved. The actual pin connections can be seen on
10
the schematic diagram of the unit. Note that the two octal sockets
different filament connections. Socket number 1 is for filaments on pins
2 and 7 while socket number 2 is for filaments on pins 7 and 8. Sockets
3 and 8 have filaments on pins 4 and 5 while socket number 13 is for
special Hi-Fi tubes with filaments on pins 1 and 2.
have
There are two novar sockets that are wired identically. Socket number
5
is for the standard novar based tubes while socket number 12 is for the
magnoval based tubes. The pins on the magnoval based tubes are larger in
diameter than the standard novar base and can damage the novar socket.
All magnoval tubes are checked in socket number 12 to prevent damage to
the regular novar socket number 5. When selecting the socket for
a
new
,
tube, select the socket for the filament wiring as well as the socket the
tube should fit into.
4
EXAMPLE
OF
SETTING
UP THE TC28
FOR NEW TUBES
Let's use for our example, the 6JE6 shown in Figure 2. This tube is a
standard novar based tube with the control grid tied to two pins on the
tube base.
FIRST: Determine the socket to use. In this case, the tube is a standard
novar base tube so that socket number 5 will be used.
SECOND: All the pins that must be isolated for testing must be noted.
In this example, we have the control grid on pins 2 and 6 and the screen
grid on pins 1 and 7 with pin 9 possibly connected to some pin internally.
With the "A" PIN ELIMINATION switch,we will isolate the extra pins.
For our example, we will push switches 6 and 7 down to the isolation
position along with switch 9 to eliminate any possibility of this pin caus-
ing a false indication.
THIRD: Determine the filament voltage. In this case, it is the 6JE6 so
that the filament switch "B" will be set to 6. The first set of numbers on
the tube generally indicate the filament voltage of the tube. On foreign
tubes, consult a substitution guide to find the filament voltage and
characteristics that can be used to check the tube.
FOURTH: Select the current range that the tube is to be checked at
using the information under "C" LOAD switch section of "SETUP FOR
NEW TUBES. For our example, the A position would be used as the
6JE6 draws a very heavy plate current under normal use. Then perform
the tests as previously described.
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