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Forced Ballast On Procedure:
The purpose is to prove that the ballast and the lamp are good (for a TV repair
estimate) in a situation where the total damage to the TV is unknown.
Procedure: Refer to figures 21 & 22.
1. Unplug the TV set. Remove the perforated ballast shield and locate connector
B2 (upper left corner).
2. Located just below B2 is the Optical isolator PC001. At the bottom of PC001,
connect (short together) pins 3 to pin 4.
3. Unplug B2 and short pins 2 and 3 of the plug. Do not plug the connector back in.
4. Plug in the TV and turn on. When the TV turns on, the ballast turns on. The
ballast circuit ignites the lamp or the spark gap (if there is a lamp defect), proving
that the ballast is good.
If neither the lamp or spark gap light, check for missing 388Vdc at B1/pin 1 - brown
wire from the power supply (use hot ground at CN005), before suspecting the
ballast.
Caution: There is over 20KV at the bottom of the ballast board.
3. Microprocessor test:
There are 2 ways to check the microprocessor output to the ballast:
a. Measure the ballast-on command voltages from the microprocessor to determine
if the microprocessor is tuning on the ballast.
b. Observe the lights on the L board to determine whether the microprocessor is
initiating a ballast-on (lamp-on) command signal.
a) Refer to figure 22. Measure the voltages at the Ballast assembly to determine if
the microprocessor is bad.
Figure 22 - Ballast On Requirements
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