Need schematic for ViewSonic PF 220

[Isaac Wingfield]

I have one with a black screen, but otherwise seems OK.

When I got it, the LM2412 video amp was blown, as well as one of the
transistors immmediately before it. Replaced those, but still black. HV
is obviously OK. Thing makes proper noises when a "sleeping" computer
connected to it is awakened.

Any suggestions?

Isaac

 

[James Sweet]

I have one with a black screen, but otherwise seems OK.

When I got it, the LM2412 video amp was blown, as well as one of the
transistors immmediately before it. Replaced those, but still black. HV
is obviously OK. Thing makes proper noises when a "sleeping" computer
connected to it is awakened.

Any suggestions?

Isaac

What voltages are you seeing on the cathodes? Does turning up the Screen
control have any effect?

Be sure to replace the 4N35 optoisolator in the power supply, these often
fail intermittantly causing the voltage to climb. Usually it blows the
vertical output chip but it could cause other problems.

 

[Isaac Wingfield]

What voltages are you seeing on the cathodes? Does turning up the Screen
control have any effect?

Be sure to replace the 4N35 optoisolator in the power supply, these often
fail intermittantly causing the voltage to climb. Usually it blows the
vertical output chip but it could cause other problems.

Sorry for the delay in responding. Our daughter is getting ready to
return to college, and everything else kind of got put on hold.

Anyway, here are the answers to your questions:

Voltages on the cathodes, measured with a "decent" scope, (at the LM2412
outputs because the cathode pins are not marked on the PCWB): ~35 Volts
tip-of-sync, ~75-80 volts peak white.

Turning the screen control about 30 degrees clockwise produces a
viewable image -- colors are off, and there are signs of video
overloading, but all three colors are definitely there, and brightness
and contrast work. Obviously, the scan system is all OK, too.

And for what it's worth, the G1 voltage is:

-38 with sync pips to -48, contrast at 100
-48 with sync pips to -58, contrast at 0

Looks like just one more voltage is still off, butI don't know which one.

Any suggestions will be appreciated.

Isaac