Sony PCS-1500 Service Manual page 146

4-1. Check Items Before Starting Self-diagnostics
2. When the IPM-92 board or IPM-93 board is suspected to be defective
. Connect the input signal as specified by the previous section. However, set the input signal level as
shown below before starting to check the circuit boards in order to reduce the external disturbance due
to natural light or other adverse effects due to noise, etc. (Select an oscilloscope setup of 20 MHz with
band-width limit: [ON.])
. Use the IPM-92 board and IPM-93 board that are known to be good and set the signal level as follows.
TP401: 2.5 Vp-p, TP421: 2.5 Vp-p (Incoming light illumination; about 1.1 mW)
. When the above described signal level is set, the normal picture cannot be obtained because the output
video signal of the DE-54 board is under the excessive input level conditions.
a) Check the modulated video signal (or carrier signal) waveform at TP401 and TP421 on the DE-54
board in order to identify which of the IPM-92 board or IPM-93 board is defective.
→ When TP401 waveform is abnormal; IPM-92 board is defective. When TP421 waveform is
abnormal; IPM-93 board is defective.
b) Check DC voltage at CN402 on the DE-54 board, or pin-5 of CN403 to photodiode (ANALOG_27
V) and pin-3 of CN403 (ANALOG_5 V) in order to confirm that the power is correctly supplied.
→ When the power is supplied correctly; pin-5 of CN402 and CN403: 27 ± 3 V, pin-3 of CN402
and CN403: 5 ± 0.5 V.
→ When the power is found not supplied correctly; refer to the next paragraph "3. When the DE-
54 board is suspected to be defective".
c) Check that the 5 V power supply (ANALOG_5 V) and reverse bias to photodiode (ANALOG_27 V)
are supplied correctly by measuring the voltage difference between pins-2 and 4 of CN701 or CN801.
→ When they are normal; CN701 or CN801, pin-2: 27 ± 3 V, pin-4: 5 ± 0.5 V
→ When they have abnormality; Soldering of CN701 or CN801 is suspected to be defective, or
flexible flat cable (FFC) has poor connection or is broken.
d) Check the modulated video output signal (or carrier output signal) waveform at D701 on the IPM-92
board or D801 on the IPM-93 board (pin-1 or pin-6) in order to check that the photodiodes are
defective or not.
→ When they are normal; FM modulated wave appears (when video signal is input.), or sine
wave of 20 mVp-p to 50 mVp-p appears. (when only the carrier signal is input)
→ When they have abnormality; The photodiodes are suspected to be defective or defective
soldering is suspected.
e) If any abnormality cannot be found by the above described checks, transistors in the range of Q701 to
Q704 (IPM-92) or Q801 to Q804 (IPM-93) are suspected to be defective.
→ Make an attempt to replace the transistors and check operation of the system. (Observe
waveform at TP401 or TP421 on the DE-54 board.)
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PCS-1500/1500P