Mac SE FEHD - first checkerboard, now stripes, looking for repair guidance

[raygank]

Hi all! First post here, hoping for some advanced help. Thanks in advance!

I picked up a Mac SE that I'm trying to get working again. It was initially booting to a checkerboard screen:


My first stop was to clean the motherboard (which didn't look too bad) with alcohol, and re-seat the ROMs and RAM and clean their sockets with electrical contact cleaner. That didn't change anything, so although the axial caps didn't look too bad I moved on to doing a recap of the motherboard.

After recapping the motherboard, I now get these stripes:


Here's a pic of the motherboard after the recap:

• I don't visually see anything wrong with the motherboard (no cap goop, all the traces look OK to my eye) but I'm no expert.
• I don't see any blown or leaking caps on the analog board either
• I disconnected the PSU and tested it with a multimeter (with no load) and I'm seeing 5.3v and 13.8v (which don't seem that bad) but only -8.2v where I think I should be seeing -12v. Not sure if this is normal.

I'm trying to figure out what my next steps should be. Should I recap the power supply, or analog board next? Or is this type of issue most likely something like a failed ROM or RAM chip or some damage to the motherboard that I'm not seeing?

Thanks for your insight!

 

[dochilli]

Check the voltages with loads. You can do this at the floppy port. Should be 12 and 5 V. Lower than 11.8 or 4.8 can cause problems.
This can be a problem of low voltages or a problem with the ROM. The SE has less problems with leaking caps on the logic board. But the analog board and the PSU have problems with leaking caps. You should recap both.

 

[raygank]

Check the voltages with loads. You can do this at the floppy port. Should be 12 and 5 V. Lower than 11.8 or 4.8 can cause problems.

Thanks. Reassembled and checked at the floppy connector. 5v seems fine (several pins read 4.9v, one reads 4.6v) but the pins I think should be 12v based on this pinout guide are reading 2.8v. Strangely, the -12v pin seems OK at -11.7v.

	At PSU (no load)	At Floppy Connector
5v	5.3v	4.9v
12v	13.8v	2.8v
-12v	-8.2v	-11.7

I'll ultimately recap everything, but based on this would you start with the PSU or the analog board? (Trying to prioritize since I can only really work on this one or two nights a week right now and I'm pretty slow at it.)

 

[dochilli]

I would start with the analog board, but I think, that this will not solve your problem. There must be something wrong in the 12v rail.

 

[raygank]

Thanks. If anyone has any advice or information about how to trace or troubleshoot the 12 V rail I’d really appreciate it.

 

[LaPorta]

id personally just recap the analog board and PSU to get that taken care of, then hunt stuff down.

 

[raygank]

It was the analog board! I still need to test a bunch of things, but I recapped the analog board and reflowed all the solder on the various 12v power connectors, and now I'm getting this:



Thanks for the help, all! I was sure I was SOL for a while there.

 

[cheesestraws]

Woohoo! Nice work.

 

[krishnadraws]

Excellent troubleshooting! Glad you got your Mac to work!

 

[LaPorta]

Very nice! I'd recoommend refurbishing your floppy drive before using it as well: