General Information; Component-Level Servicing; Stereo Module; Servicing The Power Supply - Zenith B25A10Z Service Manuallines

GENERAL INFORMATION

Servicing the CA chassis is the same as with other Zenith
single-board chassis. If the set is dead, first check the
standby and switched voltages. If the switched voltages
do not appear, check the power "On" circuit. If the power
supply is OK and the set will turn On, the Horizontal
sweep circuit should be checked next. Is horizontal drive
available from the video processor chip? If the sweep
system does not start up, sweep-derived voltages will
not be generated.
If the sweep and high-voltage circuits are OK and video
or audio are missing, then the audio/video/tuner circuits
should be checked. If the receiver is working but some
feature is not working, check the Service Menu. Bring up
the Service menu and check to be sure that all items are
set correctly.

COMPONENT-LEVEL SERVICING

The following troubleshooting information is intended
for component servicing on the 19" through 27" models.
Replacement modules are available on an exchange basis
for the 32" and 36" models.
If the CRT or Video processor IC are replaced, Black/
White tracking must be reset. Refer to the Service Menus
section of this book for Black/White tracking adjustments.

STEREO MODULE

When the MTS stereo module is replaced, be sure to
unplug AC power cord. This will ensure that the
replacement module is recognized by the microprocessor
when power is reapplied. If the set is only turned off,
the audio module may not operate properly.
After the audio module is replaced, access the Service
Menu and be sure the seven stereo adjustments are set
properly. These adjustments are Service Items #40 through
46 for the 221-1006-04 µP chip, and Service Items #43
through 49 for the 221-1006-05 µP chip. Proper settings
for these adjustments are printed on the module label
along with the bar code on the bar code label.
When troubleshooting video circuits, remember that all
video travels through the PIP IC (if used) and the Video/
Audio switcher IC. A defect in either of these IC's can
result in no video.
CM151
SERVICING (continued)
3-2
WARNING!
DO NOT disconnect the Video output module from the
CRT when troubleshooting 32" and 36" receivers. If
the video output module is removed on these sets while
power is ON, the CRT will arc and can be permanently
damaged. Also, the technician is in danger of serious
shock. There is a termination circuit (W5101) on the
CRT module to prevent this from happening

SERVICING THE POWER SUPPLY

Check the standby voltages first:
+ VDC at CX3407 (169.7 VDC when 120 VCA)
+ B at CX3420 (B is about 124 VDC for CA 25v
and 27v and 130 VDC for CA 32v and 36v)
+18 DC at CX3424
+5 DC at pin 3 of ICX3402
Check the following:
Keyboard input at IC6000 pin 7 and 8
IR input at IC6000 pin 15
Power On output at IC6000 pin 32
Q3402 power supply "turn On" transistor.
Check the Switched Voltages
+9 volts DC at pin 3 of ICX3401
+15 volts DC at CX3430
Sweep-derived Voltages
+25 volts DC at the junction of CX2105 and
RX2124
+35 volts DC at CX3253 and +200 volts DC at the
junction of CX3208 AND RX3208
CRT Filament
Check at pins 1 and 2 of connector 2F5. They
should read 6.1 to 6.3 volts AC on a true RMS
meter. They will read 7.5 volts AC on a VTVM,
and show 22 volts P-P on a scope.
VIDEO PROCESSOR ICX2200
Check the following key operating Signals and voltages:
Composite Video Out at pin 47
Switched Video Out to micro at pin 41
Tuner composite Video in at pin 37
Luminance in from PIP at pin 43
Chroma in from PIP at pin 45
CA - SERVICING