Not exactly a "Classic" Checkerboard Issue

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Last seen: 15 hours 3 min ago
Joined: Jul 14 2018 - 12:54
Posts: 146
Not exactly a "Classic" Checkerboard Issue

So I was recently given a Macintosh Classic (not a Classic II), and as one might expect, it will only give a checkerboard screen when powered. All and all, it's a pretty common issue. However, what's strange, is that the image isn't stable. Upon powering, the screen flickers, and the checkerboard is contracted horizontally with a thin squiggle that runs al the way down the screen. The image does eventually stabilize but remains contracted, also there is a strange pulsing that bulges the checker-pattern out at the sides, and slowly runs down the screen. If the checkerboard was stable, I'd assume that this was a simple motherboard issue, but the distortion, pulsing and flickering would seem to indicate something else.

I've tried cleaning the motherboard with rubbing alcohol and a cotton swab, but it didn't help. The board looks pretty clean, but there is one chip with corroded pins (labeled O, or Q-1) near the power. From the looks of it, the chip seems to have been corroded by leakage from one of the four nearby capacitors (likely C-8).

I'm considering running it through a dishwasher, but I'm not convinced that that will solve any of my problems.

I already know that I have to recap the board (there's no getting around it), but I'm wondering if anyone has any recommendations as to what replacement parts to use. I really don't want to use electrolytic capacitors again, since that's what failed in the first place, but I can't tell if the solid-state tantalum alternatives I've seen online will fit.

So does anyone have any recommendations? Will the dishwasher help? What would be the best capacitors to use so I don't have to do this again? And what's causing my screen to pulse and flicker?

Last seen: 3 days 21 hours ago
Joined: Dec 19 2008 - 21:01
Posts: 394
Likely you have a power

Likely you have a power supply problem and a logic board problem. Clean and recap and resolder may help.

Last seen: 1 month 2 weeks ago
Joined: Aug 4 2018 - 21:59
Posts: 139
Recap the analog board

Recap the analog board

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