General Category > Lisa Troubleshooting and Repair

Help please for my Lisa 2/5

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AlexTheCat123:

--- Quote ---In the meantime, I noticed in your MB wiring that the signal R1 and R2 (pins 71 and 72 of the J2 CPU Board connector) go to pins 8 of the Mem2 (R1) and Mem1 (R2) connectors, respectively. The schematics calls for these to go to Mem1 (R1) and Mem2 (R2). In other words, they were inverted. Could this explain the issue I have when I have a 512k card in the Mem2 board ?
--- End quote ---

What a coincidence! Someone else reached out to me this morning and noticed the same thing! It turns out that I somehow accidentally swapped the footprints of the two RAM slots when designing the board, so the slot labeled MEM 1 is actually MEM 2 and vice versa. This won't affect the functionality of the Lisa at all (which is why I never noticed it), but it might be a little confusing if the self-test finds a RAM error because it would report the wrong slot being bad. I already updated the Gerbers on Github to fix this problem, so anyone who makes boards in the future won't have to worry about this. I'm really sorry about my mistake!

I don't think this would cause any of the memory issues that you're seeing because my boards have the same design flaw and work fine, so it's likely to be something else!

pintoguy:
Thanks sigma7 ! Much appreciated

In response to your and AlexTheCat123 comments:

did you use an LS367 or an 8T97 for U2F? It's an LS367. I had seen your post regarding Error 57 and this chip. I'll keep this in mind

What happens if you install in Mem2, leaving Mem1 empty? Same result: garbage on screen

The I/O ROM version is collected from the RAM shared with the 6504/Floppy Disk Controller. If the 6504 isn't running, it won't have moved the ROM version into the shared RAM and you'd get random RAM contents as it seems you have. If the 6504 is fine but the CPU's access to the I/O board is not working properly, then you could have the same symptoms. If the I/O Board wasn't responding at all, you'd get a bus error, so I suspect at least some of the circuitry is working some of the time: Thanks. The 6504 was swapped with a spare one, with no change

As Alex said, only the "lower" drive is supported by the Lisa 2. The lower drive cable is the shorter one. Leave the long one disconnected (unless connected to a Sun20, X/ProFile, etc. for power). All Lisa 2 computers (aside from the ones with the internal Widget) have the two floppy drive cables, so having two isn't an indication that it used to be a Lisa 1. Thanks.I also have a spare molex power cable which I thought was there to power the twiggies. Is this not the case ?

And thanks for all other great suggestions. I'll go back to the bench this weekend, and will update !

pintoguy:

--- Quote from: pintoguy on August 02, 2023, 03:35:19 pm ---What a coincidence! Someone else reached out to me this morning and noticed the same thing! It turns out that I somehow accidentally swapped the footprints of the two RAM slots when designing the board, so the slot labeled MEM 1 is actually MEM 2 and vice versa. This won't affect the functionality of the Lisa at all (which is why I never noticed it), but it might be a little confusing if the self-test finds a RAM error because it would report the wrong slot being bad. I already updated the Gerbers on Github to fix this problem, so anyone who makes boards in the future won't have to worry about this. I'm really sorry about my mistake!

--- End quote ---

You don't have to apologize ! And yes, what a coincidence indeed !!

sigma7:

--- Quote from: pintoguy on August 02, 2023, 03:35:19 pm ---The I/O ROM version is collected from the RAM shared with the 6504/Floppy Disk Controller. If the 6504 isn't running, it won't have moved the ROM version into the shared RAM and you'd get random RAM contents as it seems you have. If the 6504 is fine but the CPU's access to the I/O board is not working properly, then you could have the same symptoms. If the I/O Board wasn't responding at all, you'd get a bus error, so I suspect at least some of the circuitry is working some of the time:

Thanks. The 6504 was swapped with a spare one, with no change

--- End quote ---

A variety of problems will prevent a good 6504 from running; Alex's suggestions to confirm it is probably working such as checking the oscillator/clock is running and the bus is active are likely sufficient.


--- Quote ---Lisa 2 computers (aside from the ones with the internal Widget) have the two floppy drive cables, so having two isn't an indication that it used to be a Lisa 1.

Thanks. I also have a spare molex power cable which I thought was there to power the twiggies. Is this not the case ?

--- End quote ---

That 3 pin cable is also in all Lisa 2 computers (unless they are wired for a Widget). It isn't used for Twiggies (or anything else that we know of).

pintoguy:
So here is a progress report after the weekend bench work

Try probing pin 2 of U7A to see if you're getting a 16 MHz clock there: Yes, I see a clear 16MHz signal

If you're getting the clock, check pin 1 on the 6504 (the reset pin) to make sure that it's getting reset at power-on. Yes, the reset signal is high, and goes low when I push the reset button

If that looks good, try probing Q0-Q3 on the LS161 at U7A. This counter chip provides the state sequences that control the operations within the floppy controller: This is a bit beyond my skill set, but signals q0-q3 do show square waves of various duty cycles. I assume it's what you'd expect ?

Also go through and probe all of the address and data lines on the I/O board ROM to make sure that they all have activity on them: there is NO activity that I can see. Would this help us ?

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