General Category > LisaList2
Another Prototype Lisa Card
stepleton:
Oh, and---those flying leads? I have a guess:
The ADC0808 near the port connecting to the flying leads is, well, an ADC, so I'm guessing that it was used to monitor certain important analog voltages in the Lisa, particularly ones that were close at hand---that is, on the I/O board. I'd bet that one of those leads would have clipped onto the screen contrast signal at one of the component legs (I don't think the I/O board had dedicated test points). Perhaps another was for the speaker volume or maybe the speaker itself. It would be interesting to know if one of the leads was ground, which would seem sensible.
compu_85:
I moved the ROM back to the card with the resistors and tried it out (briefly). It seems like the system tries to boot from it, then fails with an error 90 and some garbage on the screen.
Hers's a shaky cam video of the attempt on my 2/10, which the attached photo is a still from: https://www.youtube.com/watch?v=8UWtrU27sI0
The system does spend longer on the IO card test portion of the POST.
Also interesting is that the system comes up with a keyboard error when the IO Test card is installed. Like the first card, the system comes on as soon as power is applied.
compu_85:
The card acts a little different in my 2/5. It's able to draw the AWAITING APPLE INPUT prompt on the screen for just an instant, before the error 90 box covers it up.
https://www.youtube.com/watch?v=rq2qejCCl6M
Same keyboard error, same auto start when power is applied.
-J
Lisa2:
--- Quote from: stepleton on July 09, 2020, 08:36:55 pm ---Oh, and---those flying leads? I have a guess:
The ADC0808 near the port connecting to the flying leads is, well, an ADC, so I'm guessing that it was used to monitor certain important analog voltages in the Lisa, particularly ones that were close at hand---that is, on the I/O board. I'd bet that one of those leads would have clipped onto the screen contrast signal at one of the component legs (I don't think the I/O board had dedicated test points). Perhaps another was for the speaker volume or maybe the speaker itself. It would be interesting to know if one of the leads was ground, which would seem sensible.
--- End quote ---
Did you ever wonder why the 2/10 I/O board has a little socket next to the SCC? Maybe this is a clue to these signals....
Rick
stepleton:
--- Quote from: Lisa2 on July 11, 2020, 09:08:52 am ---Did you ever wonder why the 2/10 I/O board has a little socket next to the SCC? Maybe this is a clue to these signals....
--- End quote ---
I was wondering about that---this is actually the reason I was asking whether the black lead (attached to pin 1 of the ribbon cable) was ground :-)
Looking at the I/O board schematics on lisa.sunder.net, the files for the Lisa 1 and Lisa 2/10 boards both have the same analog circuits section, just with different labels:
https://lisaem.sunder.net/LisaSchem/Lisa1SysIO5.gif
https://lisaem.sunder.net/LisaSchem/Lisa210SysIO5.gif
They mention a J1 that appears to be a 10-pin connector, perhaps the same 10-pin connector you find on the 2/10 I/O board. (I'm too lazy to beep it out this afternoon :-). (There's also another J1 that gets referenced at the top left---that's the card-edge connector at the bottom of the board.) Instead of being ground, though, pin 1 of J1 is connected to some of the analog circuitry for the contrast latch signal.
It's possible that the ribbon cable has been plugged into the test card upside-down, but in that case I think the "pin 1" line goes to an unconnected J1 pin, according to the schematic.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version