73
17. RA-5A Protect Circuit Troubleshooting
Chapter 17 - RA-5A Protect Circuit Troubleshooting
Overview
As illustrated in Figure 17-1, several circuits are monitored for protection. Some lines are monitored by the self-
diagnostics feature while others are not. The self-diagnostics feature can assist in isolating a particular circuit.
Below is an example of the diagnostics page which is entered by pressing “DISPLAY”, “5”, “VOL –”, and “POWER”:
Self Check
2:
+B OCP
00
3:
+B OVP
00
4:
V Stop
00
5:
AKB
00
6:
Low B
00
7.
H STOP
00
101:
WDT
00
The numbers on the left indicate how many times the timer LED flashed, which designates the probable cause of
the shutdown. The flashes on the LED will occur at one second intervals, followed by a three second separation
period and repeat again. The numbers at the extreme right indicate how many times the problem occurred up to
99 events. You can see why this is beneficial for intermittent troubleshooting. It is always a good idea to clear the
events before exiting and that can be done by pressing “8” “enter” on the remote. This is not the same as
pressing these buttons in the service mode. It will only clear the events and not reset customer defaults. Beware
that the service manual instructs you to enter the service mode to clear these and that is a mistake. You can do
it right from this screen. Let us briefly cover each one.
+B OCP:
Excessive current on the 135V line. This is usually caused by flyback problems or secondary loads on
the line. The circuit could also be tripping for no reason. This is why you should always monitor AC current while
the unit is shutting down. It will help to know if you are really dealing with an over-current condition and a more
cautious approach can be taken while troubleshooting.
+B OVP
: The 135V line has exceeded 139 volts. Go back to Chapter 16 on troubleshooting regulator problems.
V Stop:
The vertical deflection circuit has stopped operating. Loads on the I
2
C data and clock bus can also be
the source of this problem.
AKB:
One or more CRT cathodes are unable to generate sufficient current to return a good feedback pulse. The
AKB detect circuit may also have failed. It is common to see multiple events in this diagnostic feature along with
registered HV failures. See the special section in Chapter 26 on AKB at the end of this manual.
Low B:
The 6.5V source from the primary power supply is monitored for excessive voltage and current. This
diagnostic label can be misleading because an OVP condition on this line will also register a failure.
H Stop:
Horizontal deflection has failed. Since the unit has a separate high voltage circuit, the set will shut down
to protect the CRTs. This will be covered in Chapter 18.
WDT:
A communications error has occurred. The main CPU is unable to communicate with the Y/C jungle IC.
The timer LED blinks continuously at one-second intervals and as soon as 101 of them occur, a failure is registered.
