HP 41CX Annunciators Become Visible with Long Inputs

[akpoff]

(01-23-2023 12:20 AM)brouhaha Wrote:  In my opinion, there's not a lot of reason to swap the logic board. I don't see any way in whcih a defective logic board could cause your display issue. The logic board doesn't drive the display segments. The serial data bus (phase 1 and phase 2 clocks, SYNC, ISA, DATA), power, ground, and a few other signals (e.g. DPWO) go to the display, and the two chips mounted on the display hybrid are the only things that connect to the LCD segments. That's why I previously thought you were talking about swapping the components of the LCD assembly, which could reveal whether the problem is on the driver PCB or the compression connector.

Ha, success! It's fixed.

Based on your comment I began desoldering the connectors, right to left. As I was desoldering the 3rd connector from the keyboard side it popped off the display as well. I was using a Hakko desoldering gun so I wasn't leaving the heat applied for long, probably a cold solder joint. I had tugged on each one to be sure they were well attached and looked at them closely. All were shiny and passed a continuity test, but perhaps the connection was just secure enough to pass a mild tug test.

I reattached the 3 connectors, put the calculator back together and voilà, it worked.

   

I had suspected this unit had prior surgery because a couple of the traces on the keyboard had solder on them. Looking more closely at the display I see the same thing.

Thanks, brouhaha, for pointing me in the right direction.

--Aaron