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17. RA-5A Protect Circuit Troubleshooting
Shutdown – No Diagnostics Indication
Since RY6001 and RY6002 are engaging, there are the five monitoring circuits mentioned earlier that will cause
the unit go into protect as shown in Figure 17-2. Monitoring AC current draw while letting the unit go into protect
will assist in determining whether the failure is current, or voltage related and steer you to the circuits to check
first.
High Current At Shutdown: If the current peaks at 3A or more, four circuits can cause this: The 19V line in the
secondary supply, the 22V line in the primary supply, an audio problem on the K board, or excessive current and/
or high voltage in the HV section. Disconnect CN2103 on the K board. If the unit stays on, there is a problem
with DC on the Speaker lines. Suspect audio output IC2601. If the high current and shutdown still occurs,
disable the secondary supply by shorting pin 1 of IC6001 to ground. Although the unit will still shut down, a
significant drop in AC current narrows the problem to the D board or an excessive load on the 19V line. If
shutdown and high current still exists, excessive loading is present on the +15v line.
Normal Current At Shutdown: This condition points to any one of the six circuits being monitored. A loss of
voltage on the 19V and 22V line will simulate an OCP condition. Any of the protect components could be
activating due to a malfunction of the components themselves. Since excessive current is not being drawn, the
risk of further component damage is minimized while searching for the cause.
CN2103 on the K board should be disconnected first to eliminate the audio circuits. If the shutdown persists,
monitor the voltage at pin 7 of IC8006 on the D board. This pin should remain low unless excessive HV has
occurred. From this point, it becomes a matter of checking voltages on the monitored lines with a peak-hold
DVM or oscilloscope.
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 18 for troubleshooting if either of these
circuits is found to be the cause.
3X Flashes: Monitor the 135V line with a peak-hold meter. If the voltage peaks above 139V, refer to Chapter 16
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 vertical circuits covered in
Chapter 18.
6X Flashes: The 6.5V source is monitored for excessive current and voltage. Check AC current at shutdown. If
high, begin unloading circuits from line. Most of the circuits using this line are in the Q box assembly so start
there. If current is low, check 6.5V level at turn on. If excessive, troubleshoot regulator stage as covered in
Chapter 16.
Note: A voltage below 1.7VDC and above 5VDC on the V sense line at pin 1 of IC6002 can generate six timer
LED flashes.
7X Flashes: Troubleshoot horizontal deflection circuit covered in Chapter 18.
Disconnect the C boards from
the tubes while working on this circuit
.
