Sony PCS-1500 Service Manual page 147

3. When the DE-54 board is suspected to be defective
. Connect the input signal as specified by the previous section.
. Select an oscilloscope setup of 20 MHz with band-width limit: OFF.
. Adjust the brightness of the incoming light until 400 mVp-p is obtained at TP401 and TP402.
. The circuit stage up to TP141 must be diagnosed by observing the waveform of the carrier signal and
by checking the operating condition with no input signal fed to the infrared transmitter. The circuit
stages after that must be diagnosed by observing the demodulated waveform and by checking the
operating condition with the color bar signal being input to the infrared transmitter.
a) Check that the DC voltages that are supplied from the power supply to the respective blocks are
correct or not.
→ When the DC voltages are normal, the voltages from MA-97 board are; TP491: 5 ± 0.5 V,
TP391: 9 ± 0.5 V.
→ When DC voltages are abnormal; Soldering of CN101 is suspected to be defective, or flexible
flat cable (FFC) has poor connection or is broken.
b) Check DC voltage at L491 and check the signal flow from TP401 to TP404. [RF amplifier]
→ When the circuit is normal, the waveforms [No. 1 to No. 5] that are shown on page 4-20 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 of Ref. 400
to Ref. 409. Replace the transistor as needed.
c) Check DC voltage at L492 and check the signal flow from TP421 to TP424. [RF amplifier]
→ When the circuit is normal, the waveforms [No. 1 to No. 5] that are shown on page 4-20 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 of Ref. 420
to Ref. 439. Replace the transistor as needed.
d) Check DC voltage at L491. [ANALOG_5.9 V]
→ When the circuit is normal; 5.9 ± 0.5 V
→ When the circuit is found abnormal; Locate the poor soldering in the circuit block in which
abnormality has occurred. Replace the transistor Q901 or others as needed.
e) Check Q110 for correct operation by observing the output waveform at TP101. [BUFFER]
→ When the circuit is normal, the waveform [No. 6] that is shown on page 4-20 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 the transistor Q110 or others as needed.
f) Check IC101 for correct operation by observing the output waveform at TP102. [LIMITTER]
→ When the circuit is normal, the waveform [No. 7] 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 IC101 or others as needed.
PCS-1500/1500P
4-1. Check Items Before Starting Self-diagnostics
4-17