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evildragon
May 26th, 2011, 07:44 PM
I have an old Mac Classic, in which case doesnt have any video output, and doest boot.

It does put up a raster though on the CRT, and sometimes it will show the grey startup screen with the mouse cursor, but the alternating checkerboarded pixels are all random, not uniform like it normally is.

Any ideas? I cant find a screw driver to take apart the computer so i havent been able to check the insides. Also, the CRT has the shakes when it does show a picture, but when its a blank raster, its steady.

RetroHacker_
May 27th, 2011, 04:11 AM
Bad capacitors on the motherboard.

This is a really common problem on these machines. Remove the motherboard and take a look at it. There will be a bunch of small silver surface mount electrolytics that have leaked and left corrosive goo on the motherboard. You'll want to clean it off the best you can (personally, I like just throwing the board in the dishwasher), and while that *may* make it work again, since the goo is somewhat conductive, you really need to replace the caps.

-Ian

TanruNomad
May 28th, 2011, 07:39 AM
I've had this problem before on a couple old macs I've picked up in the past. Just like retrohacker said, it's almost always leaky capacitors. I've never been brave enough to stick it in a dishwasher, but q-tips and isopropyl alcohol always do the trick.

Also, before you do any of that, try leaving the computer on for 20-30 minutes. Sometimes with bad caps, it just takes a lot longer for the computer to get the proper signal. This is especially true with the checkerboard type issues.

afaiello
June 12th, 2011, 04:20 PM
evildragon

Check out my thread above this one about Mac Classic low voltage on +12 V rail. My last post I mention certain bad caps on the PSU analog board. Check that out for some help.

Anthony