512Ke Video Problem

[JAG]

I picked up a sick 512Ke to rehabilitate and am stumped at what the problem is.

There is no startup `bong` and there are thin horizontal lines over the entire screen.

According to my handy copy of the Dead Mac Scrolls, that is a chip on the analog board gone bad or a programmers switch that is touching the board accidentally.

Well, I don't have a programmers switch and when I swap out the analog board, I get the same symptoms, and the machine works just fine with a different (Mac Plus) logic board.

So, the problem has to be the logic board, I think.... but beyond that, I'm not sure how to proceed from here.

Here's a picture, BTW:

 

[bibilit]

the problem has to be the logic board,

Probably a capacitor problem, try to wash the board or clean the capacitors area.

have you got the "bong" at startup or the arrow pointer ?

 

[JAG]

Nope. Nothing.

I didn't think 128k / 512's suffered from capacitor problems.

 

[bibilit]

I solved a lot of problems washing boards recently, but you can also have a look at the board with a magnifying glass.

 

[tt]

I didn't think 128k / 512's suffered from capacitor problems.

I had wondered about capacitor issues with older compact mac models, and it appears that SMT electrolytic capacitors are not used for them. But there are some electrolytic capacitors present so if you have the ability to test them, that could be one area to look. If there is no gunk leaking out anywhere, I would be surprised if a board cleaning would actually help... but it most likely wouldn't hurt the board either.

If you don't get advice that pinpoints the exact component given these symptoms....I agree intense visual scrutiny is a good start to see if anything has "burned up". If you can take well-light high-res shots of the board and post, there are more eyes available here to help.

 

[techknight]

take a blowdryer and aim them at the logic board caps. if they are bad, the more heat the better they get. Just dont overdo it.

 

[JAG]

I'll give the hair dryer trick a shot... it worked for my PowerBook 100, though I haven't gotten around to recapping it yet.

If I can't fix it, anyone have a spare 512K / 512Ke motherboard they'd like to sell? The prices on eBay are crazy (>$100)!!!