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Lots of switching PSUs are voltage-specific: if it says 230V, then don't run it on American power for sure! There may be a way to reconfigure the PSU on the inside --- something like a jumper you can move, which you find on some PSUs. But you always want to be certain with stuff like this; if...

I note this as a Revision F video board. We don't have schematics for Revision F specifically, but between these schematics for Revision E http://www.bitsavers.org/pdf/apple/lisa/hardware/050-4012-E_Video.pdf and these for revision H, with the revision notes at top right...

This explains a whole lot if it's actually the case. If you look at the bottom left of the schematic, you can see that the +5V supply is used to create a signal that inverts the horizontal drive signal (the horizontal sweep). If it's not there, then (following the trail through Q7, Q8, Q4, Q5)...

Ah, what a story! NASA was known as a major user of Lisas --- they're said to have really liked LisaProject for project management.

Looks like the right kind of thing, but U1 isn't a transistor --- it's a voltage regulator, an integrated circuit. It might not surprise me too much if U1 differed between devices, particularly if they might have been made by different manufacturers, who have designed the underying silicon...

Sorry to hear this. Does the new BU406 measure the same as the BU406 you replaced? If it does, there's still a suspicious difference that might be worth tracking down. Quick question: are both your boards the same revision? What test equipment do you have? ----- I'd now recommend having a...

Hi @Brokoli1 . 1. Did the video board work before the recap? If so, you should probably inspect your work very closely and check that there aren't errors. As you have two video boards, you may be able to compare one against the other. If not, even though there's no picture, do you have high...

I missed that you had already inspected the SRAM solder joints. If you didn't use a magnifier of some kind last time, maybe take one last look? Thanks for sharing this problem; I learned from thinking about it.

They say sometimes that it's better to be lucky than good, and it looks like we got lucky! I don't know why the computer has decided to work, but sometimes when components are marginal, on the edge of breaking, then poking at them can coax them into a working state. This is usually not a...

Videos are much harder than still images. Some rather fancy cameras allow you to choose a specific frequency for sampling frames; for others you may have to use a long exposure time and cross your fingers.

A logic analyser is a very useful thing to have indeed! I don't think that what you have here tells us much more than we already know, though. All of these signals look correct to me. We will have to check something else. ----- Meanwhile, your 'scope screenshot shows us what we expected to...

I couldn't resist studying the code just a bit more. TSTLOOP and MMUERR are dead-end routines. If the CPU winds up executing that code, there's actually no more testing being done: it's already decided that the MMU is in bad shape. What it's doing is bouncing on \RESET so that you (the...

Thanks for making all of these measurements! I think we may have made an important discovery. From the looks of things, something seems to me to be reading the ROM. That's great news, but: the \RESET pulses seem odd! But there's a chance that they could have a valuable explanation... keep...

I hope it's not unkind to ask: have there been any developments in understanding 6100 incompatibility? Did it turn out that the 7100 and 8100 have similar problems, or are they immune?

Your video board appears to me to be in great shape: it's drawing a nice, crisp display for you. It's just that the video data that it's getting from the CPU board is nonsense. The nature of the nonsense (and the reason it's different all the time) is because it all depends on whatever...

Looking further ahead, here is a kind of plan we might undertake. There may be simpler ideas, of course! I suspect that the problem we're dealing with is in the Lisa's MMU, which as Larry Pina notes is what uses the static RAM that we've been worried about. If we find that the Lisa is executing...

Ah, well that's great news. It sounds like the probing plan is back on track! Also for @BEU : An update to probing the ROMs. In the Lisa, a look at the schematics (PDF page 3 of http://www.bitsavers.org/pdf/apple/lisa/hardware/050-4009-F_CPU.pdf) shows that the ROM chips not only have a \CE...

Not a bad idea. If you know someone with a Lisa of any kind, the CPU and memory boards should basically be interchangeable. It's only the motherboard and I/O board that are substantially different, and where you will need to find someone with another 2/10. I think though that the problem is...

No worries. I am glad that you are up for this challenge! As for your documentation finding, that's very interesting --- and I stand corrected about not having any written low-level diagnostic material! I think this MMU register issue sounds like a very plausible theory to me. I expect that...

I am not writing all of this stuff because I love to type! I'm writing it for you. If we are going to solve this problem together, then I think you'll need to play an active role as part of our troubleshooting team. It's not going to work if I'm just giving you instructions from far away ---...