General Category > LisaList2
Does anyone have a spare Lisa motherboard?
rayarachelian:
Take a look here: http://bitsavers.org/pdf/apple/lisa/hardware/lisa-motherboard-enhanced.pdf
It's a bit difficult to read since it's grayscale and hasn't been cleaned up, but zoom in and it is legible.
AlexTheCat123:
I just desoldered the connector for the I/O board and I found that some of the pads underneath the connector have been corroded away. I also lifted a few pads on the bottom of the board when I was desoldering it. How should I go about repairing this damage or is the board just toast?
rayarachelian:
--- Quote from: AlexTheCat123 on November 05, 2019, 07:16:40 pm ---I just desoldered the connector for the I/O board and I found that some of the pads underneath the connector have been corroded away. I also lifted a few pads on the bottom of the board when I was desoldering it. How should I go about repairing this damage or is the board just toast?
--- End quote ---
So at this point I'd say, take a deep breath and say "It's a good day to die" like a Klingon, and then accept that this board is dead.
Now that doesn't mean you throw it out, it means you're free to do whatever you need to do to get it working again and, if you can't, you don't worry about being disappointed. However, whether you do get it to work or not, you'll have learned some really neat skills.
It's probably toast for the fully corroded pads as the corrosion will travel through the trace over time. The lifted pads might go back on if you go very gently, and they can be repaired.
You can try reflowing the solder on the corroded pads if enough material is left, then measure connectivity to the other end. If you get near zero ohms, you're fine. This is a long shot, but a conductive metal paint pen might help, likely it won't. like this: https://www.amazon.com/Bare-Conductive-Electric-Paint-10ml/dp/B00KBXT6JW/ More likely, if you can follow the trace to the other end, solder a copper wire to it and route it back to the lifted pad then solder the other end of the wire directly to the connector's pin or whatever attaches to the pad you should be good. Be sure to glue that wire down to the board so it won't move.
There are techniques for repairing lifted pads which might help: https://www.instructables.com/id/Repairing-a-Damaged-Pad-on-a-PCB/ - this following video is for SMD so it's going to be a lot easier on the Lisa. https://www.youtube.com/watch?v=YQdqX0DxBXM - google around some more, you might find better stuff than this.
Assuming you don't give up and make it to the end, once you're done and it works again, you should seal the board with some laquer - possibly krylon spray could work, or nail polish, not sure if you can get proper conformal varnish like this: https://www.amazon.com/MG-Chemicals-422B-340G-Silicone-Conformal/dp/B008O9YGQI/
I do have a similar lisa to fix, like yours, but instead, only on both a CPU and an I/O board: https://lisalist2.com/index.php/topic,18.0.html so yeah I feel your pain.
AlexTheCat123:
I just looked more closely at the motherboard schematic and it looks like most of the pads that are corroded away connect to the serial ports and the few that do not should be easily repairable. Would it damage anything if I fixed everything but the serial ports and just used the Lisa without them?
rayarachelian:
--- Quote from: AlexTheCat123 on November 06, 2019, 01:27:56 pm ---I just looked more closely at the motherboard schematic and it looks like most of the pads that are corroded away connect to the serial ports and the few that do not should be easily repairable. Would it damage anything if I fixed everything but the serial ports and just used the Lisa without them?
--- End quote ---
Unless you want to use LisaTerm or BLU or Zterm, you should be fine without the serial ports.
That said, BLU is a really useful tool, off the top of my head, I think BLU wants serial port B with hardware handshaking, so if you can fix port B, you'll be in good shape.
You'll want to at least fix the signal ground, RX, and TX lines, though you'll likely need the handshaking lines too.
see: https://www.lammertbies.nl/comm/cable/RS-232.html especially the section that shows a table labeled "DB9 - DB25 conversion" cable with hardware handshaking. The pins on the DB25 side are the ones you care about on port B.
Now, if you have a classic 68k Mac that has a GCR capable floppy drive, even if it's a super drive, you should be able to make Lisa floppies, though one with an 800k floppy drive is preferred due to the head width. And in that case you might not need to use BLU. (Don't bother with USB floppy drives, they're just MFM PC drives only - I think there might have been one that supports GCR, but they're as probably as rare as Lisa 1s.)
You'd transfer disk images to that Mac, and then make the disks on that Mac and insert them into the Lisa.
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