HP-41C LCD Communication

[haiduc32]

Thank you both for the pointers. The link was very useful. Indeed OS1 does not behave correctly and OS2 does not generate a 7khz signal.

Here's my progress so far:

After rubbing all contacts with isopropilic alcohol and resoldering all connections on the LCD it... suddenly started working! only to start working randomly... now sometimes it works, OS1 has a nice triangular wave, OS2 square. Then without touching anything it just goes to Memory Lost, or some other garbage. Power on/off also works randomly.

Assumed it could be the OS1 making a poor connection and after I disconnected OS1 and soldered a 610pF smd capacitor to ground (don't have a 470pF, but assumed should be good enough) dirrectly on the LCd board, it doesn't work. OS1 just goes to HI, and does not oscilate.

Also tried to connect OS2 to a signal generator and put 7khz, as in the suggested post. That.. was a bad idea. When powering the lab power ssupply it went all 330mA and I noticed that too late.. Half the LCd doesn't work at all now.. So.. don't try that.

Will try the next days to play around a bit more, but... pretty sure the driver is toast.