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Mac Classic in possibly dead state.

Greetings all,

I just joined the forums as I've never restored a Mac of any type in the past but I have repaired boards with battery leak damage before.
I picked up this classic for £40 from a local seller and decided I should have a go at restoring.

image0.png
It was advertised with checkerboard pattern so a re-cap would fix but when I got it home, it didn't do that and gave me an error in hitting the interrupt button:


image1.jpeg
So given it's like this, I assumed it couldn't be too bad, and then I opened it up.
image2.jpeg
The main board was stuck into the chassis with all the corrosion.

When I finally got it out it looked like this. Battery holder just fell off the board on removal. I suspect it was being held in by the case.
image3.jpeg


I've managed to clean it up a bit but the C3 cap fell off along with the Y1 component.
image4.jpeg
What is the Y1 component?

I've got some caps on order and will continue to clean and scrape the crap off the board.

Wish me luck.

!m!
 

demik

Well-known member
For a battery leakage this isn't too bad. Its does need a recap indeed.

I agree with cheesy, the error with the NMI is ok. Every old-world Mac does it. What does it do without pressing the interrupt button ?
 
For a battery leakage this isn't too bad. Its does need a recap indeed.

I agree with cheesy, the error with the NMI is ok. Every old-world Mac does it. What does it do without pressing the interrupt button ?
It just stays on a grey screen. I even tried a reboot without the HDD connected and it did the same.
I tried with <CMD>+<OPT>+X+O held to boot from rom and that seems to do nothing too.
 

cheesestraws

Well-known member
It just stays on a grey screen. I even tried a reboot without the HDD connected and it did the same.

This is actually a good thing; if it gets to a grey screen (50% dither) it means that quite a lot of the computer is working. Code has to be running from ROM and the RAM has to be at least arguably good to get to that stage. If you don't have anything running at all, that's when you get the checkerboard.

Have you unplugged the floppy drive too?
 
This is actually a good thing; if it gets to a grey screen (50% dither) it means that quite a lot of the computer is working. Code has to be running from ROM and the RAM has to be at least arguably good to get to that stage. If you don't have anything running at all, that's when you get the checkerboard.

Have you unplugged the floppy drive too?
Yes I did I think.
 

cheesestraws

Well-known member
Yes I did I think.

OK. What this probably means is that the code that's polling for a boot device is hanging, which usually IME means it's waiting on a piece of hardware to respond that just isn't responding. It polls them one at a time, so it's totally possible for a misbehaving SCSI chip, for example, to block booting from ROM. Obviously one should look at the visible battery damage first, but after that, I'd suggest looking at connections to the SCSI chip and the SWIM, based on this symptom. I can't remember if a dead RTC can cause this (given your missing crystal). I don't think it does, but I might be wrong.

That said, if it's behaving as you say, I think it probably counts as "mostly alive". Chances are good that it's repairable, IMO.
 
OK. What this probably means is that the code that's polling for a boot device is hanging, which usually IME means it's waiting on a piece of hardware to respond that just isn't responding. It polls them one at a time, so it's totally possible for a misbehaving SCSI chip, for example, to block booting from ROM. Obviously one should look at the visible battery damage first, but after that, I'd suggest looking at connections to the SCSI chip and the SWIM, based on this symptom. I can't remember if a dead RTC can cause this (given your missing crystal). I don't think it does, but I might be wrong.

That said, if it's behaving as you say, I think it probably counts as "mostly alive". Chances are good that it's repairable, IMO.
Thanks for that.
I assumed it wasn't completely dead seeing as It actually gave an error message at one point so I'm hopeful.
 

max1zzz

Well-known member
I can't remember if a dead RTC can cause this
I know the SE (Which is very similar architecture wise to the Classic) will boot fine with no clock chip installed, so it's unlikley a totally dead clock chip would cause this. A misbehaving could conceivably though. I have no idea what a working clock chip would do with no crystal, I presume it would work but the clock would just not advance
 

cheesestraws

Well-known member
I don't, unfortunately. All I have is the schematic. Did you find that? I can send it if not.

Don't worry about the traces going to the edge connector, though, that isn't actually used for anything in normal use.
 
I don't, unfortunately. All I have is the schematic. Did you find that? I can send it if not.

Don't worry about the traces going to the edge connector, though, that isn't actually used for anything in normal use.
I did get the schematic. Very helpful.
The ones I’m most worried about is the 3 pads in the middle under the battery. I’ll just reflow those when I get the iron out.
 

SuperSVGA

Well-known member
Here's some shots of that area on a slightly less corroded board.
I ended up ripping up the left trace while desoldering the holder to take these pictures. Oh well, I'll probably just put a CR2032 holder on instead.
IMG_2348.jpeg
IMG_2354.jpeg
 
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