Servo Circuit - Zenith ABV341 Series Service Manual

3. SERVO CIRCUIT

(1) Unstable Video in PB MODE
Unstable Video in
PB Mode.
YES
Does the Noise level of the
screen change
periodically?
YES
Do the CTL pulses appear
at the IC501 Pin97?
YES
Does the CFG waveform
appear at the IC501
Pin87?
YES
On tracking do the CTL
pulses move?
YES
Does the Video Envelope
waveform appear at the
IC501 Pin9?
YES
Replace the IC501.
(2) When the Drum Motor
(2) doesn't run.
When the Drum Motor
doesn't run,
Does 12V appear at the
PMC01 Pin8?
YES
Does 2.8V appear at the
PMC01 Pin12?
YES
Check the connector
(PMC01) and the Drum
Motor Ass'y.
NO
Is adjusting the height of
the CTL Head accurate?
NO
Replace the IC501.
Refer to "When the Y signal
NO
doesn't appear on the
screen in PB Mode".
Refer to "(2)
No 12VA of Power section"
Do the Drum PWM Pulses
appear at the IC501
Pin76?
Aren't the foil patterns and
the Components between
IC501 Pin76 and PMC01
Pin12 short?
NO
Do the DFG Pulses appear
at the IC501 Pin90?
NO
Do the Drum PWM Pulses
appear at the IC501
Pin76?
Aren't the connecting patterns and the Components
between IC501 Pin76 and PMC01 Pin12 short?
3-8
NO
NO
YES
YES
NO
YES
NO
YES
Readjust the height of the
CTL Head.
Do the DFG Pulses appear
at the PMC01 Pin11?
NO
Replace the Cap M.
Aren't the foil patterns and
the Components between
IC501 Pin 90 and PMC01
Pin11 short?
Replace the IC501.