Classic II vertical bars after recap & wash

[elemenoh]

This Classic II has vertical bars with no chime after a recap, rework and washing in an ultrasonic cleaner. The bars are present whether the ROMs are installed or not.

The reset button does work. It'll just blip for a moment and display bars again.

This board is the 2-ROM version. I've been testing using the 4-ROM schematics and figuring out the differences as I go.

Voltage rails are fine and the system works okay with a known-good board installed.

Everything in the voltage regulation / ADB page checked out okay except U2 pin-1 to +8v. There was no change to the symptom after fixing that.

The initial routes from every pin of the on-board RAM are okay.

I've started to test the rest of the address paths, but it's slow going.

Have any advice for where to focus troubleshooting?

 

[elemenoh]

OK I found one really dumb mistake on my part. The ROMs were in the wrong sockets. Verified they work okay in another board and put them in correctly on this board. That did change the symptom to vertical lines across the whole screen.

I've checked every address line between the ROM/RAM/EAGLE, voltage regulation, ADB and Audio and it all tests okay. I guess I can check SCSI next. Assuming the connections are all good, which ICs would it make most sense to start swap testing?

https://imgur.com/a/vJpW0Iu

 

[elemenoh]

BTW, if you have a 2-ROM board, you can use my notes in red  on the 4-ROM Bomarc schematic in the link above for your own testing.

 

[elemenoh]

I'm happy to report this Mac is alive again!

I found that pins 1,2,24 and 25, the Buffered Data lines of U14 (RAM chip closest to leaked capacitors) looked dead compared to the other three chips. The address lines all looked okay. I triple checked continuity which was fine. I had a salvage MLB (battery damage) with TMS44400DJ memory chips on it which seemed to match the HM514400AS8 chips installed. Sure enough, after replacing that chip the machine booted okay!

After sinking so many hours into this board, I feel so great to have gotten it working again. On to the next one!

 

[NECyclone]

Nice.  Well Done.