Quoted from mystman12:
Oh wow, I didn't realize the commas were controlled by a different cable on each display (I'm assuming by "top" you meant left and by "bottom" you meant right? Mousin' Around has the displays side-by-side instead of stacked). That explains why the issue is only present on the left display.
I don't have a machine with left/right configuration and I haven't examined which is left and which is right on the bench.
Quoted from mystman12:
I don't know if further testing is necessary at this point though. Like I mentioned, my logic probe is getting absolutely no signal on pin 17 of U41 (No lights, no sound), while all of the other pins output something regardless of what state they're supposed to be in. Interestingly it seems like there is continuity between other pins and pin 17 on the chip.
U41-17 is indeed the "comma" segment for the top (presumably = left) display. If there's absolutely no signal (neither 0V nor +5V) then I don't think it should light up at all but I don't know enough about how the circuit works on the PinLED board that you're using.
Quoted from mystman12:
Okay, will I have to desolder that in order to remove it? Also, since the signal is failing at U41, which is before anything goes underneath the battery, do I really need to check behind that yet? I'd rather not remove that unless absolutely necessary. Honestly if I got to that point, I'd probably just send the board in for repairs before I did anything myself... Which as of now is looking like what I'll have to do.
You should make sure you have the correct continuity from U41-17 to SRC2-9 to 1J22-26. This line runs underneath the battery holder so it is often subjected to alkaline corrosion. You can cut the battery holder off if you don't want to de-solder it. You will need some strong cutters though. If you're going to send the board off for repair make sure the person you choose to do the repair will accept the repair. Often people won't touch a board with the slightest evidence of alkaline corrosion.
Quoted from mystman12:
Also, I was going through the display test and I noticed a few other issues. The right most period on the left display will not light at all, and the right most period and comma on the right display also will not light. Not sure if that's related, but I figured I should mention it.
That never lights up during the digit portion of the test. It should light up in the segment portion of the test for either the strobes or the segments. It has been a while since I focused on that particular portion of the test so I'm doing that from memory. I'm in the process of repairing another System 11B board that has issues with U41 and U25 so once I've got all the correct continuity I'll run the test and verify that what I've written (about the dot and comma for the last strobe) is true.