Troubleshooting - Zenith CM-150 Series Service Manual

A system is easier to troubleshoot when broken down
into circuit groups. A blank display with no audio does
not necessarily mean you are working with a dead set.
Make adjustments after you isolate the problem. Do not
start troubleshooting by turning pots or using other
service controls.
Start your checks by verifying the status of standby
conditions, power on start conditions, sweep start
conditions, and then check video and audio system
conditions. The most basic test aids to use, if the set has
sweep and audio (controllable noise), are the menus and
a VCR. If there is no sweep or high voltage, then you
must make some measurements to isolate the cause to
an area of the system.
It is recommended that you perform troubleshooting in
this order: power supplies, horizontal sweep/high
voltage, vertical sweep, video, and audio.
The list of service checks on the following pages takes
you from standby to power and sweep on conditions.
Where possible, you have been given both DMM (digital
multi-meter) readings and oscilloscope observations for
the active signal checks.
MAIN
MODULE
2G3-3
CM150/PV150

TROUBLESHOOTING

TROUBLESHOOTING THE GM TELEVISION SYSTEM
A Line GM Chassis Power Control
Directview
15VDCTL
1
15V SB
PW R CTRL
12V SW
37V SBY
PW R FA
GND
GND
8
2N3-2
< > = STBY ( ) = PW R ON
HORZ DRV
VERT DRV
For most active signal checks and DC voltage measure-
ments, use the right end of RX3401 in direct view
products and the left end of RX3401 in projection
products for the DC common side of your meter or
scope. To take meter readings on the primary side of the
switch mode power supply, use front lead of RX3437 in
direct view products and the jumper W-3 in projection
products for the meter AC common.
If the audio 26VSW (connector 3K9) is missing, you may
have partial or distorted audio. The audio system is
powered by supplying 15VSB to the audio power
amplifiers, via Q4001 and Q4002, during power on until
the audio 26VSW turns on. 15VSW is supplied to IC800
and IC850 via CR801 and CR850, which prevents audio
noise during power on. When the audio 26V is present,
CR801 and CR850 back bias, preventing the 15VSW and
26V from mixing. CX848 and CX856 are kept charged to
prevent audio noise during power off.
Not Used
<15.5V> (15V)
<0V> (4.2V)
<0V> (11.8V)
<37.7V> (37.4V)
<37.7V> (37.4V)
3.5V p-p or 1.5V rms
4.0V p-p or
3-1
8
PW R SUPPLY
SW EEP
MODULE
1
3N2-2
3G2-2
GM CHASSIS