Message #5 Posted by Vieira, Luiz C. (Brazil) on 9 Apr 2002, 7:40 a.m.,
in response to message #4 by b.tokarczyk
There is a procedure I tried some times. It will probably be taken as risky by some contributors in here, and I agree it is risky. But I have done it more than a couple of times with successful results.
You will find two capacitors built in the mainboard (the bigger ones). Allow the mainboard to rest outside the calculator's box for a couple of hours and shorten these capacitors' terminals (use a piece of flexible, thin wire). Both will retain battery’s charge and keep calculator's status for some time. Shortening them will 'reset' power supply and erase all memory contents.
After that (make sure no residual charge is left in the capacitors with a voltmeter), find some conductive foam and allow the mainboard to rest over it, making sure all IC's terminals touch the foam. Let it there for a couple of minutes.
Also, check for corrosion and dust in both BATT/IO assy and the zebra connectors between the mainboard and the keyboard/display board. Sometimes a single cleanup procedure will be enough. If you find oxide residuum, some metal polishing solution will help removing.
I guess these procedures will eliminate external causes. If none of them get to successful operation, any of both the mainboard or the display assy is bad. The best shot, in this case, is having another calculator, so you can switch parts with each other and try to replace components.
If there is something else I remember, I'm posting soon. Also, if there is something else you need, let us know. I believe other contributors will try to help, too. (there are great gurus in here, it's just a matter of time for them to read this)
Hope you have success.