Quadra 840av - recapped but it has issues

[AlpineRaven]

Good morning all, 
I have been working on my 3rd Quadra 840av, It arrived to me as non working.

The 1st one - recapped - no issues and is working 100%

2nd Quadra 840av - recapped by someone else, and I've recapped it myself in case an capacitor isn't working, but lots of rotted traces, still not working - possible DOA, will sort that out one day, I've put it away for time being.

3rd one - not bad condition - but much better condition than above two 840av's but I have one issue - see below.

It has been cleaned thoroughly 3 times now, It'll fire up, it'll have Welcome to Macintosh, loads extensions as per normal, etc but as soon it launches to Finder before icons shows - incorrect clock/time message comes up then disappears on its own and freezes & the mouse disappears as well.

At first - I thought it was software issue - started up with extensions off - same thing, swapped over to known working hard drive that came out from other Quadra 840av that is running - same thing.

Swapped over VRAM & RAM from other known working 840av - still has issues which leads to focus on the logic board.

Visual inspection and checked like 6 times - it looks okay - like I said above it doesn't really have rotted traces but I can see 3 of them but looks ok/tested for circuits and its ok.

Where else should I focus on the logicboard for possible fault?

Cheers

AP

 

[Alex]

I am going to suggest it. Have you tried to kill preference files? Darn it, if possible boot from a zip with a clean install. All you need are the zip drivers on the zip and it should boot (if memory serves). Otherwise try to boot from some floppy.

A simple damaged file, like a preference file could trigger issues.

Just a though.

 

[Byrd]

Looks like you're being kept busy AP, good one

The fact you've got 1.5 working 840AVs out of three isn't bad - most were roached 10 years ago so you're doing well.  Did you get any solder pad damage while recapping?  Of the two 840AVs I recapped, both were a nightmare to desolder compared to other Apple motherboards.

I'd bench the semi-working board with known good PSU, minimal RAM, no VRAM, see if you can boot from floppy (or FloppyEmu if you have).  In terms of cleaning, noting the very fine pitched custom chips located near where caps are, a bath of white vinegar for 30 mins + gentle scrubbing with a non-static brush might help.  

 

[Microns]

Never seen these exact faults.

Random thoughts:

Have you reset the PRAM and the SMC?

Done a restart with no NuBus cards installed?

Cheers...