HP-41C with weak display

[Jose Goncalves]

I've been working on an HP-41C that shows a very dim display. In fact, it's only possible to read the display if you look at it with the machine tilted (lower part much higher then the upper part). I've noticed that batteries are gone after some two or three weeks of use, what doesn't seem to be fair.

I've been checkig for bad contacts and the like, but couldn't find anything relevant. Can someone tell me what to try next ?

Thank you

[David Smith]

Try cleaning the circuit boards with 91% isopropyl alcohol. I have seen this happen when old solder or some other gunk gets on the boards. Clean the CPU, keyboard, and back of the LCD. Another symptom that shows up is a display that only shows up while a key is pressed down.

Be careful not to get the alcohol on or under the LCD window. It can cause it to appear fogged. On full nut machines you can remove the LCD module and repolish the window (but this is a fairly tricky thing to do).

Another cause may by the temperature compensation circuitry in the LCD drive system.