Still have power supply issues with my Classic 1

[benanderson89]

Hello again everyone! My Macintosh Classic is still being a pain in the backside. Today I replaced DP 3, 4 and 6 (though I've not done the opto isolator yet), and I'm still having issues. Screen shaking and taking a long time to reach a bootable voltage as per this thread from early October still apply. However, after replacing those three diodes it's somehow even worse!



Not only do I still have screen shaking issues, it took a solid two and a half minutes to reach a bootable voltage (although it has been switched off for nearly a month) -- though unlike before the screen never stabilised even after ten minutes. When you kill AC power the shaking suddenly stops for the split moment it's running off of the excess charge in the board's capacitors. Something isn't filtering the AC voltage properly.

Anyone have any ideas I could try to save me taking it to a repair shop?

 

[warmech]

though I've not done the opto isolator yet

I'd bet money on this being a culprit; I've had a few Macs with image geometry/stability issues before and after recapping where it turned out the opto IC was at fault. While this won't solve all of your issues, it is a cheap fix that more than likely will address part of them. My other bet would have been on DP6 as well, for what it's worth.

 

[benanderson89]

I'll give that a bash sometime today! Thankfully I already have some compatible opto chips in the garage so I can just fish those out.