128k Mac with mods (512K + SCSI?)--can't remove motherboard due to add-on circuit board interference

[Bench]

I have a 128K Macintosh that I have had since new. Some time in the late 1980s I had it modified--added RAM (expanded to 512K ?) and added SCSI--I think. I haven't used it since the early 1990s and it has been in storage since then.

After reading postings in this forum about compact Macs, I realized it might have battery and capacitor leakage problems that should be addressed.

So yesterday I pulled it out of storage to begin the inspection process.

The battery was luckily leak-free but measured only 2.2v--so that has been discarded.

For the motherboard inspection, I disconnected the floppy drive ribbon cable and the wire bundle from the analog board. Then I attempted to slide out the motherboard but ran into obstructions due to a secondary circuit board that sits about 1/2" above the motherboard. I can't get a real clear view of this secondary circuit board but I can see that it has some RAM in slots and a connector for a ribbon cable that runs out to another connector that mounts over the battery compartment--this is for the SCSI connection--I think.

Because of the motherboard's extra height due to the secondary circuit board with the RAM and SCSI connector protruding above that, the RAM and SCSI connector contact the converging plane of sheet metal frame that sits above it. First of all, I removed the SCSI ribbon cable from the secondary circuit board. Then I was able to deflect the secondary circuit board just enough to overcome the contact with the board-mounted SCSI connector and slide the motherboard out a little farther. Then the RAM contacted the same part of the frame. Again, I was able to deflect the circuit board enough to clear the contact and slide out the motherboard a little more.

But now both the RAM and the SCSI connector seem to be contacting the converging frame, preventing the motherboard from sliding out any farther. Things seem wedged in pretty tight right now. I'm not sure I can safely deflect this circuit board anymore.

If this was a common modification to the 128K, maybe someone here has seen this problem before.

Is there a better way to ease this motherboard out of the frame or does it just take brute force?

Thanks

 

[olePigeon]

You can't slide it out anymore.  It'll take some effort, but you have to bend outward either the left or right side of the chassis that holds the motherboard.  Once you pop out the side of the board, the rest will follow.

 

[Elfen]

WAIT!

One of the sides of the logic board zig zag notches with large square teeth. Push the board back in slowly until you see the tabs line up with the 3 metal legs on the frame and the board can be flipped out like a page in a book! You need to see this at the bottom side of the Mac as you slide out the board. You do not have to slide it out all the way. Just pull back the board about an inch or a bit more for the tabs to line up to the frame...

What you are lining up with:

 

[Bench]

Thanks for the tips, guys.

First of all I carefully lowered the logic board to relieve any stress I had induced in trying to remove it the wrong way.

I checked the edges of the logic board for any notches (if I understand correctly) but both edges are straight corner to corner with no notches--at least on this board.

I looked closely at those metal wings. The wing on the same side as the analog board had clearly been slightly mangled previously no doubt to install the modified logic board back in the day. So I just carefully bent that same wing outward just enough to release that edge of the board and then was able to remove it.

 

[avadondragon]

The notches mentioned aren't on the 128k macs - just on the later models.  I guess Apple realized it was impractical to have to slide the board all the way out and any mods make it really hard to remove.  I have to bend the frame like that on my SE because of a Radius accelerator which makes it impossible to move the PCB at all.  Man I hate doing that!

 

[james_w]

Oh avadondragon that's really useful to hear - I've got an SE with an accelerator that I was completely stumped by - I'll carefully bend the frame to get it out. A recap needs doing!

 

[Bench]

Now that I have the logic board removed, I can see that the add-on board is a Mac Rescue. I did a search on "MacRescue" in this forum and found a prior thread that addressed this board removal problem and solution.