Macintosh Classic PSU problems

[quantumii]

Hi,

A while ago I got hold of a nice little Macintosh Classic. It works, but the internal HDD does not spin up when connected to the internal PSU (It spins but stops), and the monitor has a shaky picture, and with every mouse click the screen contracts a little. Same for floppy reads (even more) and sound output

I connected a scope to the +12v and +5v lines on the HDD power supply cable, and sure enough, the voltage fluctates quite a lot, and you can see it sag in unison with the monitor wavyness and the floppy reads etc..

Question is, where to look first? Any specific caps I should replace :?:

Thanks

 

[tomlee59]

Check all connectors (unmate them, clean contacts, remate). Carefully inspect the solder joints associated with those connectors.

Carefully look at the electrolytics -- in most cases, you will see telltale smudges where these caps have started to leak. You'll need to clean the board thoroughly and replace the caps (not just the ones with obvious signs of leakage; they'll all need to be replaced). I recommend tantalum caps (these have no liquid electrolyte).

Connector cleaning, resoldering, and recapping generally takes care of the most common problems in these Macs.

 

[quantumii]

Thanks, I will do the above, and hopefully that will restore it