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[ried]

Looking to buy a working Lisa PSU in case anyone has one for sale. Can be either the original for the Lisa 2/5 or the 2/10's 1.8A DataPower unit (preferred). Thanks in advance 

[ried]

Alternatively, if anyone has the ability to repair my 1.8A unit, I would certainly like to enlist his services. I've re-capped it to no avail, however.

[pintoguy]

fwiw, I had fought some PS issues a while back (see post in 68kmla) https://68kmla.org/bb/index.php?threads/i-think-i-have-graduated.31754/

I solved the issue by changing the pulse width modulator chip Z2 (SG3524)

[stepleton]

I repaired my own 1.8A PSU the exact same way.

But what do you observe about your broken PSU? How does it not work?

[ried]

Thank you, gents! Mine was working just fine until a week or so again and then... lifeless. No activity whatsoever when the power button is pressed. Confirmed that it's the PS after swapping in a working Datapower unit. I'm not sure what changed?

Will follow the other thread and investigate further. Thanks again.

[stepleton]

It could be all kinds of things. Something might have shorted and blown a fuse. Like ours did, the SG3524 chip may have died. Perhaps the voltage protection is malfunctioning and shutting the PSU down prematurely. Maybe the panel interlock microswitch broke. There is a troubleshooting journey ahead of you, in other words!

Of course, troubleshooting power supplies is a tricky business and dangerous if you don't know what you're doing. You might want to set aside this challenge for later when you've picked up more skill, the same as I've done for a few projects.

[ried]

Of course, troubleshooting power supplies is a tricky business and dangerous if you don't know what you're doing. You might want to set aside this challenge for later when you've picked up more skill, the same as I've done for a few projects.

Wise words, as always. To eliminate the SG3524 chip as a possibility, I swapped the small (controller?) board for a known good one from my other, working DataPower unit. No change. So, I suspect it's somewhere on the main board? Could be the microswitch, or any number of things as you mentioned.

[stepleton]

That's great --- you've hopefully eliminated a bunch of possibilities that way!

One way you can be even more certain is to put the small board from your broken PSU into your working DataPower PSU. If it works in there, then there's very little question that the problem in your broken PSU is elsewhere.

The small board is indeed a kind of controller module. I may be misremembering, but I think it largely corresponds to the second of these two reverse-engineered schematics for the PSU:

https://lisa.sunder.net/LisaDataPower-1-B.pdf
https://lisa.sunder.net/LisaDataPower-2-B.pdf

I think that DataPower must have done things this way so that they could reuse this controller for a variety of different power supplies. If you change the values of the resistors that you find on the card, you can change the voltages that the power supply will produce. I can think of at least two other PSUs in my collection that use the same kind of modular design.



And I should apologise for my phrasing: I think I must have been writing while I was listening to something else. I should have said that if you were feeling uncertain then it's worth considering setting the project aside. It sounded like I was presuming things about the current state of your skill, and I didn't mean to do that!

Finding a mentor to work with who's local to you is another good option if you're not too sure what's what. It's not always easy because folks like that can be hard to find, but if you can track someone down, it can really speed your learning. (Often good mentors have good tools as well )

Another thought: give the "mainboard" a good close inspection for cracked solder joints?