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Macintosh SE/30 good chime, but not booting


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  • 68kMLA Supporter

Hi all,

 

I have three SE/30s, one works flawlessly (Mac A), one boots into the OS but has sound has issues (Mac B, I have another topic about this one), but my issue is with the latest one (Mac C):

 

When I got it, I did a superficial check and turned it on and it booted (without chime) into the :?: screen. It looked pretty corroded (and no sound) so I decided on a cleaning and recap.

After the recap was done, I got a nice clean chime, but now it no longer booted to the :?: screen (see video.)

During the recap I noticed the corrosion had eaten away the trace next to the negative lead of C2 which I patched by running a wire from pin 5 on UB10 to pin 50 on UI8.

The other thing I did to it was remove, clean and re-solder UC8.

 

I mentioned the other SE/30s because I thought I'd try to debug this issue by measuring (in diode mode) IC values against the other Macs. The weird thing is that both machines that boot into the OS have different values on the IC I re-soldered (UC8), pin 11 has OL on Mac B, but 1.100 V on Mac A, so I don't really know where to go from here.

 

Has anyone got any idea what a gray screen is about? Or any other hints?

 

I've included a couple pics of the board.

 

Thanks!

 

IMG_3063.JPG

IMG_3060.JPG

IMG_3059.JPG

IMG_3058.JPG

IMG_3057.JPG

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  • 2 weeks later...
  • 68kMLA Supporter

I did some more research into the issue (good chime, gray pattern, no pointer), but so far haven't found that particular combination.

The ones I did find are:

  • [no chime, gray patter, no pointer] -> RP2 filter
  • [good chime, gray pattern, pointer] -> RP10 filter

Both measure (using resistance) the same as my known-good board, so I think the filters are good.

 

Sources for above symptoms:

https://web.archive.org/web/20160306072255/http://www.biwa.ne.jp:80/~shamada/fullmac/repairEng.html

http://www.maccaps.com/MacCaps/Repair_books_files/Mac Classic %26 SE Repair and Upgrade Secrets.pdf

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Also, are you absolutely POSITIVE the trace wire you ran to fix the broken trace are the actual pins? I dont have an SE/30 board in front of me so I cannot verify. That is the only thing that has changed since before and now according to your explanation. 

 

Otherwise, this is caused by the SWIM not initializing. SWIM/SCSI are connected together through a group of VIAs that get eaten away by the 3 caps next to the molex so you need to grab the schematics and ring those ICs out back to where they are supposed to be. 

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@MikeatOSX I scrolled (ha) through the Dead Mac Scrolls but couldn't find this particular issue.

 

@techknight I'm pretty positive, according to schematics I could find it is called BRST and I'm guessing that means something-reset? Thanks for pointing me to the SWIM (UI8, so it could still be my patch that screwed something up), I'll focus my next bit of debugging on that area.

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oh wait, that's not the SWIM, that's GLUE. The trace runs between the right channel sony chip and the GLUE chip. SWIM is UJ11 of course. Still, I'll check the area around C9-10.

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@techknight, you are my hero. After desoldering the three caps below J12 (just so I could have a better look at the traces that run underneath them I spotted 1 going between C8 and J12 that had the protective layer removed and that had probably shorted C8. cleaned everything up again, put a piece of kapton tape over the trace and resoldered the caps and now it boots again!

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