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Macintosh SE FDHD - can't find MOBO 820-0250-A schematics

Posted: October 15th, 2020, 7:28 am
by Agrax
Hi to everyone!

I am new to the forum, and need some help with my Macintosh SE FDHD.
I just refurbished and fixed one Macintosh Classic and it works perfectly except SCSI HDD (which sometimes requires side kick to start spinning), for which I already purchased SCSI2SD on eBay and can't wait for it to arrive.

Anyway, I started refurbishment of mentioned Macintosh SE FDHD which was in absolutely terrible condition due to battery leakage (more like battery explosion, as it looked like from inside), everything was oxidized ... totally dead. I washed every part of it, besides HDD and floppy, as I did with Mac Classic and I managed to recap everything (except HDD and floppy drive ... really not deeded) and I fixed analog board (few transistors and diodes were shorted). I had to swap RAM with new RAM sicks (now it has 4MB), but when I plug it in and turn the switch ON, HDD starts to spin, but screen is totally black.

OK, I did not put any battery back to the mother board (I will ... these days), but this should not be the reason why the screen is black, right?
I know that there must be some signal generated by that big VLSI chip, but I cannot probe it with the scope because I do not know where to start since the schematics for Macintosh SE is nowhere to be found on the Internet. Of course I can look for datasheets of the ICs, but it will take forever.

To be more specific the motherboard model is 820-0250-A (1988). I found some schematics for SE/30 but not for SE FDHD.

Does anyone has schematics for motherboard model is 820-0250-A for SE FDHD, or maybe knows where to find it?

If you do, please share.

Re: Macintosh SE FDHD - can't find MOBO 820-0250-A schematics

Posted: November 9th, 2020, 11:54 pm
by corkonthefork
You may benefit from Kai Robinson's SE Reloaded project where he is rebuilding the SE logic board.

Please take a look at the following link:

And consider corresponding on what you need on the message thread (don't have the link handy) on

Re: Macintosh SE FDHD - can't find MOBO 820-0250-A schematics

Posted: November 18th, 2020, 1:10 pm
by Agrax
Thank you corkonthefork for the suggestions.
After talking to people on in last few days I managed to repair Mac SE by bending IC legs on BBU chip, after many hours of tracking possible faults on PCB with scope and magnifying glass.
Now, I am planning to buy another SCSI2SD on eBay to make it perfect ... what a beautiful machine.