Sony KDP-57XBR2 Training Manual page 7

FB621
R607
4.7 OHMS
D601
D602
R620
FROM
T601/1
AC Hi
SIDE
S
C608
R604
HOT
GROUND
Troubleshooting
This supply should operate reliably since it only feeds a few circuits and the current demand is minimal.
Unfortunately, as this supply is always running so long as AC input is supplied, it will be susceptible to line
transients. The main supply will be protected as long as the main relay is not engaged and the transient is not
large enough to jump the open relay contacts (such as a heavy lightning strike). Failures that might occur would
be a dead supply or regulation problems.
If Q601 has shorted, there is a high probability that something else caused the failure. This is based upon a
reliable history of this component. We will start with a scenario of a shorted Q601 and then cover a "no run"
condition next since you are most like to end up with this after replacing Q601 due to current or transient causes.
The FET gate has very high impedance, which allows other components to suffer damage.
Dead standby supply - Q601 shorted
Upon replacement of the shorted FET, the main concern is what caused it to fail and to prevent it from failing
again when power is re-applied. The most valuable piece of test equipment in this situation, as mentioned in the
beginning of this manual, is a variac with an AC current meter, either separate or integrated with the voltage
meter. This will assist by indicating current conditions, and allow you to control that situation and prevent failure
of the newly installed FET.
C617
D623
R609
D
C614
R616
Q601
D607
2SK2845
D604
MTZ-T-77
-15
R608
R622
C609
Q602
PROT.
C613
R605
FIGURE 3-1 - STANDBY SUPPLY
C616
R615
R638 D610
D605
RD6.2ESB2
C618
C610
4
3. RA-3/3A Power Supply Troubleshooting
T602
SRT
1
11
2
3 10
7.2VDC
D667
4 9
C676
5 8
6
G BOARD
2TVP14
TO RY601
POWER RELAY
IC655
5V REG
BAO5T
CN605
I O
10
G
STANDBY
C650
+5V TO
A BOARD
CN681
7/11/02