General Category > Lisa Troubleshooting and Repair
Restoration of a Lisa 1
rayarachelian:
--- Quote from: snuci on May 17, 2020, 06:29:24 pm ---It might also be the axial caps but I usually don't see those type going and they look visibly okay.
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There are in circuit capacitor testers out there for $50~$60, might be worth using one of those to save more time later on. Hopefully all the chips on the questionable board are socketted. From Tom's photo, at least those are.
--- Quote from: stepleton on May 17, 2020, 07:15:30 pm ---PS: How difficult was it to remove the drive belt from the spindle? I've never attempted it.
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And an even better question, how would one go about building a new belt? Not that I own any twiggy drives, but that's something that's bound to eventually dry out and fail.
snuci:
--- Quote from: stepleton on May 17, 2020, 07:15:30 pm ---As a computer scientist I have to recommend doing a binary search among your chips :D
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Well, swapping all chips on the bottom board swapped the issue so it is definitely one of the chips. Thankfully, they are all socketed. That is very good news but now I have to swap chips one-by-one or half at a time to narrow things down. I do not have replacements for most of them and the ones I do I have already tried replacing with no luck.
The problem is that inserting a disk or formatting will cause the head to go to the outer track on the disk and it cannot find the right speed as it tries several before it gives up and displays an error in BLU. If I write a disk from memory, it starts and the inner track and writes out and it does several tracks until it fails as it travels towards the outer tracks.
--- Quote from: stepleton on May 17, 2020, 07:15:30 pm ---PS: How difficult was it to remove the drive belt from the spindle? I've never attempted it.
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Actually, it is very easy. It's very much like a bicycle tire. You pull up on one side of the belt and turn the center spindle until it comes off. To put it back on, you put it on the motor side, then put the belt on one side of the center spindle side and start turning the center spindle and it belt eventually evens out and it's on. The belt is made up of woven fiber rubberized material that is quite strong and will last another 30 years. It has not stretched at all which is a bonus.
Getting closer...
blusnowkitty:
I can't say if it's applicable to your case with Twiggy disks, but my 2/5 had an issue where it would attempt to format a disk but fail to verify until I replaced P6A. Might be worth checking out if you have a spare one of those, unfortunately it's a custom Apple part.
snuci:
The problem chip was the MC14015B 4-bit shift register on the bottom board. Swapping this between drives makes them work/not work depending on which drive the bad chip is in. I ordered an MC14015BCP so I should do some final testing when it arrives.
I have a scratchy sounding drive that I tried to grease the rails but still seems scratchy. I'll have to do my best to clean it while I wait for parts. Stepleton, have you had to clean your drives at all?
stepleton:
I was cleaning the drive a couple of weeks ago, as a matter of fact---you can see where I was asking for tips beforehand here.
But I took a minimalist approach inspired by the assembly guide I mention in that post. I decided not to lubricate my drive rails and suspect that they weren't ever lubricated---I could see no sign of any kind of grease on them, and when I dusted them with a tissue there was no residue. I think the "teflon coating" referred to in the assembly document is a permanent coating.
I wound up cleaning the little channel in the casting where the "frog leg" roller goes---seems to me like it may have had a bit of graphite lube on it---and put down a bit of polyolefin grease there. Meanwhile, the manufacturing instructions specify Tri-Flow PTFE lubricant for the stepper motor lead screw, and while I don't have any to hand, I've ordered some and will add a few drops later on.
None of my ministrations so far have changed how my Twiggy drives sound---mildly suggestive of snapping themselves to bits during disk insertion and ejection, the same way they've done for the last 22 years :D
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