LisaList2

Good news about the boards! They were stuck on that same production stage until yesterday, at which point they jumped all the way to fully completed. Not just fully completed as far as PCB fabrication is concerned, but fully completed in terms of both fabrication and assembly. Not sure why the tracker hadn't been updating for so long, but the boards have now shipped and should be here on Friday!

Thanks thats good to know! I wondered if this helped narrow it down to more likely being an I/O board issue versus a CPU board issue. I am going to try to probe the 556 tomorrow through the top with the I/O board installed. If there is anything else you suggest me checking let me know. Relatively new to using a scope and this level of electronics diagnostics so appreciate the help from everyone so far.

Quote from: pugy365 on March 08, 2026, 09:41:10 PMOk so I attempted to probe it, but have been doing most of my probing with the I/O board removed so I can get to the back of the CPU board. Noticed something new, with the IO board I get the beginning of the self-test procedure and image on the screen (but no clicking of the speaker) and error 41. I understand this error is I/O board related, since it's removed. But curious I get this with it removed an no farther than H with it installed. It also appears to be constantly doing a redraw, made a GIF to show here. Also pin 9 is constantly HIGH no toggle. I think I may be able to get to it from the top with the cover removed.

That constantly redrawing error 41 is the exact behavior that you should expect to see from a Lisa that's missing its I/O board. So don't worry too much about that.

As @sigma7 said, the issue with the I/O board is likely something to do with a bus error when trying to communicate with the floppy disk controller shared RAM. The Lisa does this when clicking the speaker to figure out the system type and adjust the frequency accordingly, but something seems to be going wrong during these communications.

My first guess is that the floppy controller simply isn't generating DTACK. And if not that, then DTACK somehow isn't finding its way back to the CPU.

Ok so I attempted to probe it, but have been doing most of my probing with the I/O board removed so I can get to the back of the CPU board. Noticed something new, with the IO board I get the beginning of the self-test procedure and image on the screen (but no clicking of the speaker) and error 41. I understand this error is I/O board related, since it's removed. But curious I get this with it removed an no farther than H with it installed. It also appears to be constantly doing a redraw, made a GIF to show here. Also pin 9 is constantly HIGH no toggle. I think I may be able to get to it from the top with the cover removed.

Quote from: pugy365 on March 08, 2026, 07:31:33 PMclicking multiple times a second, so very fast like click,click,click one after the next. Screen is static from what I can tell, I don't see any obvious redraw just get stuck with the H but clicking continues.

Looking at the Boot ROM listing, at $0B24, just after the click procedure has started, the ROM checks the I/O Board ROM version so it can adjust the output frequency according to what kind of I/O board it is.

At this point it hasn't fully loaded the VIA hardware for the click, but it may have done enough to cause a noise to be generated. However, if the I/O board doesn't respond when the 68K tries to check the version, a bus error will be generated. Normally such a bus error is expected and handled, rather than causing a loop, so if this is what is happening, I'd guess that the problem is actually further up the chain on the CPU board.

So, I suggest: check the bus timeout signal on the CPU board (the 556 at U15B-9) to see if it is toggling when the clicks occur.

Also I just tested with using either RAM cards in both slots and behavior is the same. I also did test with no RAM card installed and I get the clicking speaker but no video if that helps at all.

Thanks All! To confirm behavior clicking multiple times a second, so very fast like click,click,click one after the next. Screen is static from what I can tell, I don't see any obvious redraw just get stuck with the H but clicking continues. Note that clicking stops for maybe a little longer than a second if I press reset but then as it boots it come back. I will check my 5v rail again, it seemed ok but possible issues as I haven't recapped that yet. Yes along with the RIFAs been waiting on the smoke haha. Now that I have some life those components are in the mail along with an ESProfile hard drive simulator.

Quote from: pugy365 on March 08, 2026, 09:11:33 AMI was now able to get a stable image.
...
Image is below but basically only a capital H but still the constant speaker clicking.

Nice progress!

AFAIK, this is not a common failure mode. The usual constant clicking occurs when the PSU over-voltage crowbar is triggering constantly, but you don't get video in that case, so probably not your situation. (You could watch the 5V rail to be certain.)

Please be more specific as to the timing/context of "constant clicking" ...

eg. Is the video static at that screen with the H in the menubar and the speaker clicks every half-second?
or
Does the screen re-draw in some fashion, draw a blank menubar, click, add the H, wait 10 seconds, then repeat?

The SRAM on the CPU board is part of the MMU, a portion of RAM on one of the memory boards is used for the video bitmap.

Congratulations! That's progress. So the machine powers on and begins executing its boot ROM, but freezes before the power-on self test and its CPU board icon appears...

The good news is that the power supply and the video board seem to be working fine. On that front, you will likely need to replace the RIFA film capacitors in the power supply if they are original, as they are likely to release the magic smoke at any time now.

As a next step, I would try ruling out any issues with the RAM boards. Try pulling them and testing them one at a time, each board in both memory slots. If the POST is stalling out due to a RAM issue, having one working RAM board in a working slot might enable you to make further progress during POST.

Progress update, after using some deoxit on the video board trim pots I was now able to get a stable image. Image is below but basically only a capital H but still the constant speaker clicking. I believe I should see the self test at this point but I don't get that far. I do at this point have a keyboard, mouse and floppy disk connected.