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23. RA-6 Protect Circuit Troubleshooting
Shutdown – No Diagnostics Indication
The first step necessary is to listen for the sequence of relay clicks when the unit is powered up. If two clicks are
heard less than 500ms apart followed by a third click at least one second later, the protect circuit is activating.
The initial rapid clicks indicate the main supply is powering up and the inrush relay RY6003 is activating. If only
one click is heard, AC current must be monitored to determine whether the power supply is starting or RY6003 is
defective. If current above 500ma appears, the supply is starting and the unit is shutting down because RY6003
is not engaging. Troubleshoot RY6003, PH6002 and its associated components. If no current is read, the power
supply is not starting; refer to Chapter 22.
The next circuit to check before moving on to the voltage protection lines is the V Sense at pin 1 of IC6003. A
DVM with peak-hold is recommended. The DC voltage must be more than 1.8V and less than 5V. Any deviation
from this indicates resistance value changes in the voltage divider network or a loading of the line by protect
diode D6009. Once the inrush relay and V Sense circuits are eliminated, locating the protection line causing the
shutdown is necessary.
NOTE: Beware that a V Sense anomaly can cause the self-diagnostics to flash the LED in sequences of six,
indicating a loss of 5V which is monitored by Q714 on the A board. This is a quirk in the diagnostics circuit. Even
though the LED is flashing six times, the event is not stored in the diagnostics failure history. Over-current
conditions on the ± 15V lines have also generated six flashes.
All of the low B+ voltages on the secondary of T6001 are monitored for the loss of these voltages. There is no
current protection. Only the 135V line is monitored for over-current and this is displayed in the diagnostics
feature. Even though an over-current condition may have been the original cause, these lines are protected with
fuse links. One or more of the fuses may be open causing the shutdown. Checking the fuses with an ohm/meter
is the preferred initial step. If a fuse link is found open, troubleshoot that line for a possible loading problem. The
only line that is monitored for over-voltage is the regulated 6V from IC5004 by zener diode D5018.
Shutdown – Diagnostic Indication
2X Flashes: Verify a legitimate over-current condition by monitoring AC current at shutdown. If high, disable HV
circuit first, followed by horizontal deflection circuit. Refer to Chapter 24 for troubleshooting. If the AC current
does not exceed 2 amps at turn on, IC5002 is firing. Check the IC and possible R5102 open.
3X Flashes: Monitor the 135V line with a peak-hold meter. If the voltage peaks above 139V, refer to Chapter 22
for troubleshooting regulator problems.
4X Flashes: Check the DC voltage at the clock and data lines at main CPU IC001. The voltage should be
4.6VDC. If either is low, locate the component loading the line. If OK, troubleshoot the vertical circuits.
6X Flashes: The 5V source is monitored for loss by Q714 on the A board. IC12 on the A board regulates the 6V
from the power supply. Verify the presence of 6V entering the A board at CN4-3 and 5V exiting IC12.
7X Flashes: Troubleshoot horizontal deflection circuit covered in Chapter 24.
Disconnect the C boards from
the tubes while working on this circuit
.
8X Flashes: High voltage has exceeded specified limits or there is excessive current in the flyback transformer.
Refer to Chapter 25.
9X Flashes: The audio output IC has shorted or the protect components on the A board have failed
