Repairs, on-board RAM and 475 / 575 boards

[Jagmn]

I have now 'repaired' two boards (one each of a 475 and a 575) where some/much of the data/and/or/address lines under the on-board RAM have been destroyed. In both cases, I've been able to get enough bodge wires in place to be able to get the boards booting without the on-board RAM (just enough lines repaired to boot from a SIMM). I have had to either re-purpose pads for the on-board RAM as part of the bodge or there were simply too many tiny traces side-by-side for me to attempt a full repair that involved restoring the on-board RAM.

I'm curious:

1. How many other members have seen similar failures in boards they've repaired?
2. What did you do about it?

 

[imactheknife]

I have now 'repaired' two boards (one each of a 475 and a 575) where some/much of the data/and/or/address lines under the on-board RAM have been destroyed. In both cases, I've been able to get enough bodge wires in place to be able to get the boards booting without the on-board RAM (just enough lines repaired to boot from a SIMM). I have had to either re-purpose pads for the on-board RAM as part of the bodge or there were simply too many tiny traces side-by-side for me to attempt a full repair that involved restoring the on-board RAM.

I'm curious:

1. How many other members have seen similar failures in boards they've repaired?
2. What did you do about it?

I have recapped a quite a few 475 and 575 that have never had this issue. Although one 475 board i have Chimes but never gets past that (new pram battery etc). Wonder if some trace is broken under a rsm chip? What was some symptoms of yours?

 

[treellama]

I re-capped a 475 and it required a patch to one of the SCSI data lines to get the internal 50 pin SCSI working. The whole back side of the board has this weird white particulate sediment or like stress pattern from flexing, I can't tell what it is. Hard to know what happened to the thing. It's working fine now with that one trace repaired.

 

[Jagmn]

I have recapped a quite a few 475 and 575 that have never had this issue. Although one 475 board i have Chimes but never gets past that (new pram battery etc). Wonder if some trace is broken under a rsm chip? What was some symptoms of yours?

The one I repaired most recently had some (impossible to visibly locate) broken traces between MEMCjr and the SIMM / on board RAM. The symptom for me was that it 'bonged' fine without a SIMM but did not boot, yet gave death chimes with the SIMM installed.

After a lot of buzzing around with my multimeter, I found that the A9 signal was broken somewhere hard-to-locate, and that several of the signals going through the on-board RAM area were not reaching the SIMM or only reaching some of the on-board RAM chips. Your problem could be there; but a 'quick' test would be to make sure all your RAM address/data/CAS/RAS signals go to the right places.

 

[GRudolf94]

My Q800 board had a grenaded DRAM area from the battery going. I've simply not bothered reinstalling the onboard DRAM, as, aside from the missing pads and corroded traces, some ICs also had missing pins. Just patched it thru, left the DRAM out, and I can compensate for the lack of the onboard 8MB with larger SIMMs.

 

[Bolle]

How many other members have seen similar failures in boards they've repaired?

I've got a couple of non-working 475 boards with suspected failed traces. Symptoms vary from no chime at all, chime and then nothing afterwards, chime and kind of working only when the board is flexed in some way...

What did you do about it?

Fix all traces in one go

 

[Jagmn]

Well that's fun Is this the near-conclusion of a recent project?

 

[Bolle]

Very recent… it just booted for the first time today after a week of troubleshooting unable to find a single signal that shorted to an adjancent pin under the DFAC.
Diagnostic mode spitting out an Egret/Cuda error wasn’t actually helping much steering me into the right direction.

 

[olePigeon]

@Bolle Just out of curiosity, do you have each of your clone boards framed and put on your wall? Cuz that's what I'd do if I was making all these cool boards.

 

[Bolle]

boards framed and put on your wall

 

[olePigeon]

View attachment 66776

 

[Jagmn]

Very nice

Will you make a variant that can take a LTC1799 for overclocking? Like a built-in Spicy-o-Clock?