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Lisa Video, ProFile power issue, NiCad Leak fixes, etc.

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AlexTheCat123:
You guys helped me fix my heavily corroded Lisa a while back, but unfortunately it's having problems again. I started having problems where it wouldn't turn on and when it occasionally would power up, it would give error beeps indicating that the I/O board was bad and the CRT wouldn't display anything. I got tired of the corroded and flaky I/O board, so I ordered a bare I/O PCB from John at VintageMicros around a week ago and got it fully assembled. I also made an X/COPS to replace the COP421. Now the computer will turn on when I press the power switch and the CRT turns on, which is an improvement, but clearly things still aren't working right (see the attached picture). There is also no sound of any kind from the speaker (no clicks or beeps). I'm assuming that this problem has something to do with the CPU board since it handles video generation, but I can't really probe it with the oscilloscope to figure anything out since it's inaccessible while the card cage is installed. Does anyone have any tips or suggestions of what to try next? Thanks for the help!

rayarachelian:
It could be something to do with the VSROM which is used by the video state machine to generate the horizontal and vertical sync signals.
Could also be an issue with the RAM.

But both of these would indeed point to the CPU board, if there's not even a beep it could be the CPU never starts (although a bad COPS VIA6522 would stop it from beeping even if the CPU is running.)

See if you can hook up your scope to ground + one of the CPU pins, maybe A1 or D0 and see if anything is moving there. That would at least tell you if anything's running.

AlexTheCat123:
I just probed the address and data lines of the CPU and there's definitely activity. What should I try next?

rayarachelian:

--- Quote from: AlexTheCat123 on May 28, 2021, 02:19:47 pm ---I just probed the address and data lines of the CPU and there's definitely activity. What should I try next?

--- End quote ---

That's a good sign. I'm guessing the RAM boards are ok as they worked before, right? You could also try with just one CPU board or the other if you happen to have two.
Without RAM, there's nothing that can be displayed.

I'd look at the CPU board schematics and locate the VSROM and the things it talks to - that's the video state machine. Something around there's not working - though it could be something related to the analog board. I do see some diagonal lines on the display, those are a sign that some horizontal retrace is happening.

I take it you've played around with the trimpots on the video board using a plastic screwdriver already.

Some other things to try, pin #19 (CB2) on VIA #1 (with the other end to GND) produces sound via a timer + shift register output so I'd attach the scope to that and power it on, it might be trying to beep some codes but if the speaker isn't working you won't hear them. The scope should be able to pick up the tones graphically and you could figure out what they're trying to say: https://lisafaq.sunder.net/single.html#lisafaq-hw-rom_beeps - you might have trouble telling high vs low tones apart graphically if they're all high or all low, so you might need to guess around those codes. Might help if the scope has some audible mode to help you with that, or if you have something you could attach to that pin that leads to an amplifier - but be careful not to fry your VIA.  An old pen style logic probe that beeps might do the trick to get sound out also.

If you see nothing, either the CPU can't talk to the VIA or something else is broken along the path from the CPU board to the I/O board.

If you have a spare VSROM to swap out that would help eliminate that. If not you might try this one: https://www.ebay.com/itm/142796459701 - but it could also be something else around there.

Inserting a blank or PC formatted floppy might be useful too though it might also eat it and not let go until you fix the problem - the idea here is that it will see the floppy as unreadable and should eject it. That would tell you that the 68000 and the Boot ROM are working.

Another thought which you might be able to verify if you don't detect any beeps: Since you're not seeing video, and you're not hearing beeps or clicks or anything like that, it might also be the motherboard. Perhaps some contacts aren't touching or are dirty and so the CPU board video state machine can't read the RAM and turn it into a video signal and it can't talk to the I/O board so it can't beep.

Checking for broken solder joints on the motherboard where the CPU connector is might help, as would cleaning the contacts, reflowing the solder, etc.

AlexTheCat123:
Good news! It lookes like one of the address lines going to the CPU was broken, so I patched the trace and now it actually displays something meaningful on the screen! It's great to have the Lisa at least sort of working again after months of attempts to fix it. Both the CPU and memory boards pass the self test, but the I/O board takes around 20 seconds to test (I remember it testing almost instantly back before I started having problems with the computer) and it gives an error code of 57. I also hear a beep code, so the speaker seems to be working as well. I looked up error 57 and it seems to be related to the floppy disk controller, but the schematic for the disk controller section of the I/O board looks pretty complicated and I'm not really sure where to start for troubleshooting this section of the board. Also, the ROM revision for the CPU board correctly shows up in the upper right hand corner of the screen as revision H, but the I/O ROM shows up as revision 00, which definitely isn't right. Please note that I am using the Sun Remarketing 800K ROM instead of the original Apple one.

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