Help Repairing an Apple Composite Monitor IIe A2m6021X

[matsondawson]

Hi,

I have this monitor and it's producing raster but I'm getting no video. Video is working on other monitors.
I have oscilloscopes, HV probes, the works so tools aren't an issue.
Has anyone got a repair manual or any guidance?

Cheers,
Matt

 

[Hugo Holden]

The first step is to check the simple things. Check the video input connector and the wires/connections leading to it. Rotate the contrast control a few times in case it has gone open circuit.

If the fault persists and you could post the schematic of it, if you can get it, I could advise with you with scope to trace the video signal through the signal process circuits etc. Generally there are a few stages of video amplification and the sync pulses are split off fairly early.

Even though there is no video visible (a blank raster) is there sync lock ? You could tell by rotating the vertical hold control and seeing if you can get a rolling black horizontal bar.

 

[matsondawson]

Thanks for the input. I turned it on yesterday and there is no longer raster.
I opened it up and traced the composite as far as a large I.C. and it was connected at least that far.
I tested all the transistors and diodes with the multi-meter in diode test mode and they seemed ok.
Since there is no raster anymore, I tested if I was getting heater and HV (I am). But testing what I'm guessing was the horizontal deflection transistor I found there was no input to the base leg.
I'm guessing that if there appears to be no signal the monitor turns it off?
The PCB is very impressive with silk-screening that makes it easy to track where everything goes, so I'm hoping if I can figure out some way to get access to the PCB while the display is on I should be able to track where I'm losing the video signal.
My guess is a dry joint, as when i got it, it worked for about a minute before getting in to this state. And having the raster come back when I got the monitor out of storage a subsequently disappear again makes me think doubly so.
I'll keep you updated.
Thanks for the reply.