Apple 2c IIc video issue

[coolate]

Hello!

I am having a strange issue with my Apple 2c. It will boot up fine, but after it warms up which takes about 30 seconds the text starts to get distorted and fuzzy.  It keeps getting worse until it can't be read at all. Turning it off and on again does nto effect it unless I let set unplugged for 5+ min then it works fine for another 30 seconds. I can still type and run commands fine, I just can't read/see anything. It is a rev 2(0) board with no mods. I looked at the board and did not see any caps leaking. I did swap the 6 biggest ones to see if that was it, no luck. I also unplugged the floppy, and it makes it take longer before glitching out, maybe 2-3 minutes vs 30 seconds, so that makes me wonder if it is in the power board.

Any ideas?? I have uploaded a video so you can see the distortion. https://youtu.be/3pZoFFXiKlo

Thanks!! 

 

[CC_333]

I don't know much about Apple II's, but that looks to me like it might be a power supply problem (the fact that unplugging the floppy drive delays the onset of this "fuzziness" makes me think of power supply even more).

c

 

[coolate]

Hey,

Thanks for the reply!

An update: Still no luck. I now have changed all but a few caps. The PSU voltage to the board seems to be stable and stays the same before and after. It's not perfect, but I assume close enough. 12.3V, 4.89V, and -11.8V. 

Any other ideas?? Oscillator somewhere?

 

[gilles]

maybe a bad ground in the cable? It does not seem to be a big issue. the screen is a TV ? pal or NTSC IIc ?

 

[Gorgonops]

They sell this stuff called "Freeze Spray" for troubleshooting electronics, specifically the case where something starts off working okay but acts up as it gets hotter. I wonder if getting a can of that might be worth your while. Squinting at bad scans of the Apple IIc's schematics it looks to me like the video sync signals are derived from the "IOU" ASIC, UE14. I *kind* of wonder if it could be failing. (Those ASICs in the IIe/IIc are *pretty* reliable but they do go bad. It's bad if they do, of course, replacements can be hard to come by.) Might be interesting to spritz it with freeze spray and see if it walks back the glitching.

 

[Eric672]

@coolate did you ever get your issue sorted out?  I am having similar issue with a recent IIc+ pickup.