Power Supply; Ac Input; Ac Input Troubleshooting; Emi Filter - Sony CPD-420GS Training Manual

Power Supply

Overview
The power supply in this unit is a switch mode power supply. The power
supply is rated to operate with an AC input voltage range of 100V - 240V.
Current input is 1.2 - 1.7 A. The output of the power supply produces
+180V, +80V, ±16V, +12V and +5V DC from the AC input. In addition, it
provides +6.3V DC for the CRT Heater and an isolated ±8V DC output to
the Horizontal Centering circuits. It has a fold back mode used for the
Power Saving and Failure (Shutdown) operations. This chassis incorpo-
rates the use of a single power supply control IC601. IC601 provides
most of the power supply control except for output power switching pro-
vided by Q602 (POWER SWITCH).

AC Input

The AC input section provides EMI filtering, input protection, surge limit-
ing and CRT degauss operation.

AC Input Troubleshooting

For No Power or Dead Set condition, the AC Input circuitry should be
checked. F601 should be checked for continuity. CN603 to the H Board
and the AC power switch S601 should be checked for continuity. Further
checks should be made to R602, TH600 and D601 respectively if no prob-
lems can be identified.

EMI Filter

The EMI filter comprises X - capacitors C601 and C602, Y - capacitors
C603, C604, C605 and C606 and the line filter transformer LF602. Input
protection is provided by F601 and surge current limiting by thermistor
TH600 and resistors R602 and R603.
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Degauss Circuit

The Degauss Circuit is used to demagnetize or degauss the CRT. During
'Active On' mode, the Micro IC1001/5 (N Board) sets the Degauss signal
to digital H (+5V). The Degauss signal via CN1001 pin 25 to CN801 pin
25 (D Board) is applied to Q670 (DEGAUSS SW). Q670 turns ON and
activates relay RY601. This allows AC current to flow to the degauss coil
through posistor THP602. The current heats up THP602 posistor and its
affective resistance increases. This dampens the current in the degauss
coil to nearly zero allowing the magnetic field to decay gradually. After
approximately 5 seconds, IC1001/5 sets the Degauss signal to digital L
(0V). The Degauss signal via CN1001/25 to CN801/25 (D Board) is ap-
plied to Q670 (DEGAUSS SW). Q670 turns OFF and deactivates relay
RY601. The degauss coil should sufficiently demagnetize the CRT.

Degauss Troubleshooting

The malfunction of the degauss circuit can be a loss of the degauss signal
from the N Board. The +5V DC degauss signal can be checked at CN801/
25 and should be present for approximately five seconds once AC power
is applied. The activation of RY601 through Q670 can also be heard.
Further checks to THP602 and VA601 should be checked respectively.
Another method of verifying the degauss circuit operation is to use the
manual degauss operation found in the OSD menu.