Commodore PET Single Horizontal Line

[seanduffy]

I recently got a Commodore PET 3032 Series from eBay, its previous owner said that it had worked perfectly the last time he used it, but that it hadn't been touched for about ten years. When I powered it up, the monitor displayed a single horizontal green line and nothing else. Pressing the keys has no effect. I don't think it's very likely that I'll be able to fix it/have it fixed, but still I'd like to try. What kind of thing would cause a problem like this? Even if someone could tell me if this is a problem with the display unit or with the logic board, that would be a great help as I can't find any information about anyone else having this same problem.

Thanks in advance!

[LoneWolf33]

Hi,

There might be problem with the vertical deflection in the CRT display, some possible reasons:
- the driver circuit of the vertical deflection is defective
- failure of the vertical deflection coil (short circuit or discontinuity)
- no vertical sync is generated or the VSYNC pulses are not reaching the vertical deflection driver
(I'm not sure about that is it a composite video signal passed to the monitor or the H/V sync is
handled separately)

This last one is related to the motherboard. The presence of the VSYNC pulses can be traced back
with an oscilloscope. If someone could provide a schematics, maybe I can help more.

[LoneWolf33]

Update: I've checked the schematics diagrams found on this site, and the horizontal and vertical sync signals
(generated by the CRT controller IC) are passed separately to the CRT display (non composite signal).
So it is relatively easy to track the vertical deflection control signal's path from the CRT controller IC to the end
of vertical deflection drive circuit.