Message #1 Posted by Pavel Korensky on 13 Oct 2003, 9:57 p.m.
This night, I had a really funny time with my HP-41CV.
I was reading some materials about HP-41 synthetic programming on my PC and I played with my HP.
Suddenly, the calculator died. Totally. No ON, no "Memory lost", nothing.
Hmmm, it seems that the batteries died. So I put a fresh set of batteries into the calculator and....
So, I removed the batteries, short contacts for couple of seconds, put the batteries back in, switched ON and...
At this time, I started to be a little nervous. Maybe I finally discovered how to fry the HP-41 via synthetic programming. :-)
I took the calculator to my workshop, disassembled it and I tried to short a capacitor. I assembled the HP together, put the batteries in, switched ON and...
I disassembled the calculator once more and I applied 6V from my power supply directly to the PCB. Switched on and bingo, the HP works again. So I tried to look at the flexible PCB battery contacts.
Yes, there was a big crack in the flex PCB, just at the + battery contact. It seems that it was just a coincidence that the calculator finally died during my experiments with synthetic programming.
So, it was necessary to repair the battery contact. I used the following method (I do not know is this method was posted here in the past. If not, maybe I should call my patent lawyer :-)))
Those flexible PCBs are made on Kapton foil. It means that you can solder them without any problem, because the Kapton will not melt. You only need to solder quickly, otherwise the plastic parts around will start to melt.
I have a couple of thin copper foils in my workshop. I bought them couple of years ago from McMaster-Carr. They are 0.05 mm thick. I cut a small piece (approx. 7 x 3 mm) of the copper foil, applied a lot of SMD flux (from the flux pen) to it on both sides and with the soldering iron, I put a small amount of solder on both sides.
After that, I put a good amount of flux to the battery contact and applied a small amount of solder on them. Finally, I put the foil to the contact and applied a small amount of heat to it. The foil was nicely soldered to the flexible PCB and the contact is like new. :-)