Zenith C27A25, Service Manual

Page: 27 / 59

CM152
3-1
XC - SERVICING
SERVICING
GENERAL INFORMATION
Servicing the XC 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 Factory Menu. Bring
up the Factory 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 FACTORY MENU
section of this book for Black/White tracking
adjustments.
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.
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
(R5110) on the CRT module to prevent this from
happening.
If the microprocessor (IC6000) or the EEPROM
(IC6001) are replaced, be sure to check the values
for all factory menu items. It may be necessary to
manually change every item by one value, then back
again to then desired value. This assures that the
data is all correctly saved in the EEPROM. Failure to
do this may produce unpredictable behavior in the
TV and in any other TVs which are cloned .
SECTION 3