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[ried]

While using my Lisa 1, the mouse suddenly stopped tracking its horizontal motion. I figured one of the mouse's internal IR transmitters / receivers on the horizontal axis had gone bad, so swapped the mouse for a known working unit. No dice. The horizontal axis of the second mouse wasn't registering any significant movement on the screen, either. A slight jitter when moved horizontally, but that's all.

Huh.

I tried re-seating the card cage, the I/O board, cleaning the connections on each (as well as the mouse port) and still... no dice.

Through trial and error I found that the built-in Parallel port seems to be generating interference. By leaving the Parallel port empty and booting the machine from the Parallel expansion card, the mouse's full functionality was restored. I tried a different cable with the built-in Parallel port and regained some (but not all) horizontal tracking. That's how it remains now. If a ProFile drive (or drive emulator) is attached to the built-in Parallel port, I lose some or all horizontal mouse tracking. If I keep that port empty, the problem goes away.

Vertical tracking is unaffected and works properly in all cases.

Any ideas what might cause that? Thanks in advance.

[sigma7]

Lisa 1 ...

The horizontal axis of the second mouse wasn't registering any significant movement. A slight jitter when moved horizontally, but that's all.

the built-in Parallel port seems to be generating interference. By leaving the Parallel port empty ... the mouse's full functionality was restored.

Each direction of mouse movement has two signal lines that toggle in quadrature fashion so the direction and amount of movement can be detected. A jitter only response on one axis suggests one of the signal lines is working, and the other is not.

The horizontal axis of the mouse is pins 4 and 5 of the mouse connector. These connect to the I/O Board edge connector at pins 89 and 93.

It looks to me that the only parallel port signal that is close to these is the DB-25 pin 25 "Chk" signal that is connected to the I/O edge connector at pin 92. It is connected to the COPS as "M3" and the schematic implies this was for the third button of a potential/imagined three button mouse. The ProFile controller connects this to ground.

My guess is physical or corrosion damage to the motherboard or I/O board has connected pins 92 & 93 or something along those lines.

[ried]

Brilliant analysis, thank you! I have taken the card cage out and inspected the I/O board, as well as its socket, for any signs of corrosion or debris that could be causing an issue. Clean as a whistle. Bright, shiny contacts and no signs of contact are present.

I do wonder, however... Before the issue arose yesterday,  I was re-assembling the machine and decided to clean the contacts and socket with Deoxit to ensure everything was perfect. I wonder if a liberal application of Deoxit might be causing crosstalk of some sort between the pins? I wiped the board dry, and blew out the socket with air and wiped it dry as well. But I wonder if there's some amount of Deoxit still present under the socket that could be causing the issue. I suppose we'll find out if it dries and resolves itself after a few days.

Will report back.

In any case, thank you again. The amount of insightful and detailed information shared here on the List by yourself and others is truly remarkable. 

[ried]

Well, I can't confirm this 100% just yet but the mouse tracking has steadily improved over the last couple of days. No obvious cause. It's now working properly 99% of the time, and only very briefly loses horizontal tracking for a second or two now.

I do wonder if it was the Deoxit that I applied to the socket. Did it enable crosstalk / interference between the two pins that sigma7 mentioned? I would not have expected that to happen.

If the issue returns we'll know that my hypothesis is incorrect.

[stepleton]

This should be testable... Squirt enough contact cleaner into a paper cup or a dish to make a little puddle. Then jab in the probes of your multimeter on ohms mode. If the reading is still in the megaohms or more, even when the leads are close together (but not touching), then I would bet it was something else.

[ried]

Good idea. Just tried and confirmed: Deoxit is not conductive at all.

In any case, the issue has fully resolved itself after a few days. Horizontal mouse tracking is back to 100%. I really wish I knew why, but I'm going to chalk that up as another vintage computer unsolved mystery for now.

Thanks everyone.