Commodore 1084s moving display

[Sanxion]

Hi all,

My 1084s has started to develop a "moving display". When I turn it on, the picture moves both horizontally and vertically. Sometimes the horizontal movement will gradually slow down to the point you think it will stabilize itself but will then speed up again.

Where should I start to look for the fault?

[darkspr1te]

that sounds like caps in the horizonal/vertical have gone bad and the voltage is unstable feeding both those systems,
try here for some info,
https://www.eevblog.com/forum/repair/repair-commodore-1084s-p/




but if you have not done a cap refurbish I would, also the variable resistors could do with some contact cleaner and if you have it a dab of switch grease (white grease) for the future




darkspr1te

[elecdonia]

Did these old monitors use a multi pin cable where the horizontal and vertical sync were on separate pins? IIRC the original 15-pin analog VGA cable had dedicated pins for H and V sync.
A broken wire in the cable or a bad connection could interrupt the sync signal. This would cause the observed symptom.

Electrolytic capacitors do fail, but they aren’t the cause of every fault.

[Sanxion]

Interesting you should say that. When I returned to this monitor recently, the picture was stable but severely distorted. When fiddling with the vga plug, the picture would alter. I then removed the back and I noticed the pins of the vga socket were moving in the holes when pressure was applied to the connector. I then reflowed the solder on the connector pins. That improved the quality of the picture but the image started moving. So I am wondering if it is something that I actually caused?

[agent_power]

Those monitors often suffer from dried up and cracked solder joints. You can check some things:

- Are the switches in the back in the correct position for your video input
- Does it also happen on other inputs (composite, S-Video)
- Did you excercise / clean / set the knobs related to the screen settings
- Is your cable good

Wiggling or tapping certain things could also help in finding the fault, should it be a loose connection

[elecdonia]

Yes. You might have created an open circuit or a short circuit.

Check the schematic to determine which pins carry which signals. The sync signal (or signals, sometimes H and V are on separate pins) should consist of logic level pulses. Easy to diagnose with any oscilloscope. Doesn’t need to be a fancy oscilloscope.

[Sanxion]

I found the problem. On my working 1084s, there was a connection between pin 8 + 7, composite and horizontal sync. On my non working 1084s p1, there wasn't. So I bridged between those pins and..