13
4. RA-3/3A Shutdown and Self-Diagnostics
5
6
2
3
7
1
8
4
8
9
8
7
4
R665
R664
R663
R659
R661
D672
C662
C663
R691
D674
D675
MTZJ10B
D663
D661
Q654
R675
Q655
Q658
R690
D680
D676
MTZJ-3-9B
C680
R686
C679
R687
C676
D667
D651
R688
D664
MTZJ-2-7A
IC655
BAO5T
5V REG.
I
G
O
R689
R662
R657
R654
R667
PART
OF T602
STB
STANDBY
5V
TO
Q652/B
RELAY
DRIVE
OVP
OCP
RELAY
TO RY601 POWER RELAY
+135V
FROM
D652/A
AND D653/A
STANDBY 5V
RY DRIVE
FROM
Q652/C
IC651
OVP/OCP
uPC393C
-
+
-
+
+135V
BRIDGE
NEG.
FIGURE 4-1 - POWER SUPPLY PROTECTION
PROTECTION
LATCH
CN605
TO CN681
A BOARD
R681
R660
TO Q656/B LIMITER
4.1TVP14
7/11/02
R682
D668
24V
Q657
C678
D669
13V
R684
+18V
+11V
G BOARD
Protection Circuits Not Covered By Self-Diagnostics
There are four protect circuits that are not monitored by diagnostics. Consequently, they will not be identified by
the timer LED or stored into the diagnostics page. Referring to Figure 4-1, the standby 5V regulator IC655 is
protected against over-voltage to its input and excessive current at the output. The 11V line on the secondary is
monitored for excessive current (or a complete loss of it). The 18V secondary line is also monitored for over-
voltage. If the unit goes into shutdown with no diagnostic indicator, this is where you will want to look next. Here
are some quick methods to locate the source:
The Standby 5V Circuit: Monitor the anode of either D675 or D674 while applying AC power. An oscilloscope or
peak-hold DVM is preferred, but this can be done with a standard DVM. If anything higher that 600mv appears
at this point (you will see 10V or more if this circuit is firing), the input voltage to IC655 is exceeding 10V and firing
D675. Troubleshoot the standby supply regulator circuit described earlier in this manual. If D675 is not firing,
read the voltage across Q658 B-E. If it is 600mv, the OCP circuit is activating. Locate excessive load on standby
5V circuit. If Q658 B-E remains at less that .6V, monitor Q658 collector while re-applying AC. The voltage here
should be zero. Any rise indicates excessive 18V or loss of 11V.
18V and 11V Protect: Monitor the voltage at D669 cathode while applying AC power. If voltage peaks at 11VDC,
suspect 11V line failure or shorted D669. Normal voltage should be around 18V. If the voltage at Q657-E is
higher than 24VDC, the 18V line is too high. If both voltages check OK, look for leaking or shorted zener diodes
D669 or D668. Q657 may also be leaking or shorted.