Help with HP 41C display

[jwhsu]

As part of a bundle I obtained for a HP 41CX, I found a disassembled HP 41C in the box. The calculator was in good condition, however, there were no screws and the plastic sheet to protect the back of the keyboard was missing. The I/O block was also badly corroded and there was a cracked post that was repaired with what looks like epoxy. I purchased one of Diego's Flex-PCB boards from The Calculator Store to repair the block. I also had some styrene sheets handy to cut to form to protect the keyboard. I asked Monte to send some extra screws when I ordered his CL board (thanks Monte). When I put everything together, I was greeted with a beep and a "MEMORY LOST" on the LCD. However, when the calculator is on idle/standby, the display is blank. I can see the numbers/characters on the LCD when a key is pressed. As far as I can tell, there are no other problems with the calculator (all keys work, no problems with the display elements). I looked again at the area around the broken post (picture attached). The traces appear to be intact and the solder joints appear fine. Is this a condition that is repairable or will I need to look for another calculator to convert to a CL? Thanks for your help.

   

[rwiker]

I think I had a similar problem when I first set up my 41CL. In my case, the display was faint, and I discovered that there is a way to adjust the contrast by software. I'm really hazy on the details, but I think I used functionality in a module to make the display legible.

See, e.g, this post.

[emece67]

I've encountered a similar problem months ago. Finally solved it, perhaps your case is similar. See here.

Regards.

[jwhsu]

(11-17-2015 08:24 PM)emece67 Wrote:  I've encountered a similar problem months ago. Finally solved it, perhaps your case is similar. See here.

Regards.

Thanks for the information. I built your circuit and tried it out. It drove the LCD to where instead of individual characters, all the elements were powered on. It must of done something to the circuits on the LCD board because when I removed the oscillator and powered up the calculator, the LCD was working perfectly. I'm not sure what happened, but I now have a working 41C which is now being converted into a 41CL. Thanks for the help.

[emece67]

Happy to be useful, even in such unexpected way.

Regards.