HP 71b repair advice - won't power on with batteries or on AC adaptor

[Dave Frederickson]

(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?

Another cost savings with regard to the plastic-backed 71's is rather than using heavy metal shielding, the inside of the case is sprayed with a silver-colored metallic coating.
In the photos it can be seen that this coating has been attacked by the corrosion and is flaking off.

The PCB's can easily be separated from the case halves after the two wires to the beeper have been desoldered. Remove as much of the flaking metallic coating as possible.

Also of interest, sometimes the corrosion turns the PCB solder joints black. These black solder joints are very difficult to desolder. I suspect the surface of the solder joints has been altered and raised the melting point. Any insight into what is going on would be appreciated.

Dave