Sony PCS-1500 Service Manual page 148

4-1. Check Items Before Starting Self-diagnostics
g) Check IC121 for correct operation by observing the output waveform at TP122. [DEMODULATOR]
→ When the circuit is normal, the waveform [No. 8] that is shown on page 4-21 can be obtained
with no input signal fed to the infrared transmitter.
→ When the circuit is found abnormal; Locate the poor soldering in the circuit block in which
abnormality has occurred. Replace IC121 or others as needed.
h) Check DC voltage at L492. [Power supply line of low-pass filter (integrator)]
→ When the circuit is normal; 5.0 ± 0.5 V
→ When the circuit is found abnormal; Replace L192.
. When no input signal is fed to the infrared transmitter
i) Check waveform at TP141. [Low-pass filter (integrator)]
→ When the circuit is normal, the waveform [No. 9] that is shown on page 4-21 can be obtained.
(no input signal fed to the infrared transmitter)
→ When the circuit is found abnormal; If any output signal is generated while no input signal is
fed to the infrared transmitter, it is considered abnormal because the carrier signal without any
input generates no output signal after it is demodulated.
* However, when an infrared transmitter is not operating (in such cases that the main power of
the infrared transmitter is not turned on), some output signals are generated because the
system noise or external disturbances due to natural light is amplified by the limiter.
. When color bar signal is input to the infrared transmitter
j) Check the output waveform at TP141. [Low-pass filter (integrator)]
→ When the circuit is normal, the waveform [No. 10] that is shown on page 4-21 can be
obtained.
→ When the above waveform cannot be obtained, the circuit is suspected to be abnormal; Locate
the poor soldering in the circuit block in which abnormality has occurred. Replace Q140 or
others as needed.
k) Check IC141 (1/2) for its correct operation by observing the output waveform on TP142.
[DE-EMPHASIS]
→ When the circuit is normal, the waveform [No. 11] that is shown on page 4-21 can be ob-
tained.
→ When the above waveform cannot be obtained, the circuit is suspected to be abnormal; Locate
the poor soldering at R148, R149, C147 and C148. Replace IC141 or others as needed.
l) Check IC142 for its correct operation by observing the output waveform at TP143.
(Video signal check) [VIDEO AMP]
→ When the circuit is normal, the waveform [No. 12] that is shown on page 4-21 can be
obtained.
→ When the above waveform cannot be obtained, the circuit is suspected to be abnormal; Locate
the poor soldering of resistors and capacitors in the peripheral of IC142. Replace IC142 or
others as needed.
4-18
PCS-1500/1500P