Mac IIsi repair attempt, take 2

[Big Ben]

Hello there

With lockdown I decided it's time to dig into some long post-phoned repairs, start with the mighty and wicked fast the "LC" look-alike Macintosh IIsi!

I bought it on ebay for a fair price, it was out of order of course, but it was, electronics aside, in a good condition.

This one is almost a stock one with a 40MB disk, a Nubus adpater + FPU (MC68882) card and a Asante Ethernet card

The amazing TO DO list for this IIsi

• Clean and recap the PSU, which was just soaking in his own "cap-goo". Yikes.
  
• Clean and check the floopy drive
  
• Check the hard drive
  
• Clean and fix the motherboard
  

Let's start with the last one, the motherboard, previous owner already tried to fix the computer replacing the motherboard can capacitors. It didn't work and he didn't go further.

It wouldn't have worked anyway because the PSU was (and still is) dead.

This one haven't suffered from a leaking battery but caps leaking was heavy on this one, and the previous repair was quite bad.

First step was to remove the caps, and do a first clean up.

Tomorrow I'll try to remove most of the corrosion and do the recap.

 

[Big Ben]

Here is a small update,

The leak as done a nasty job, the corrosion is quite heavy. Before doing a first test after recap, I was pretty sure it ain't be successful, alas, this IIsi didn't prove more wrong.

Using an ATX PSU and matching the power connector pinout, I was able to start the computer but so far:

• no chime
  
• white screen
  
• no access on floppy/hard drive
  

Points I've checked so far:

• 12V seems fine
  
• 5V seems fine too
  
• On board ROM and jumper properly set
  
• PRAM battery is good
  

So I'll be going back to the workbench trying to narrow down this problem.

 

[bibilit]

Not sure a 100 % but on some units (IIci / Classic) the Sony chips are part of the processor reset line function.

i have no schematics for the IIsi, but as those are near the capacitors and pretty dirty, maybe a clue...

 

[Big Ben]

I've got some schematics, unless I'm wrong this is not the case on the IIsi. But I missing a page just near the part with the 2 Sony chips.

I'm definitely going to check this first, I repaired a LCII with the same behaviour due to a bad ground connection on a chip managing the reset line.

I don't know which part is responsible for the reset, it looks like it's the MC34064 and the 68HC05.

 

[Papichulo]

This is exactly what im dealing with. Any update?