HP-50G Excessive Battery Drain / Fix?

[jebem]

(05-27-2015 05:27 PM)HrastProgrammer Wrote:  Thanks for the suggestions, I will try them ...

I got it for cheap so I will keep it anyway. But, as I wrote in the first post, what concerns me is how something like that could happen and how to prevent such failures with new calculators.

BTW, it looks like 50G has screws beneath the LCD cover so it can be opened much easier than 49G+:

Ah! Yes, I totally forgot about that video! Excellent demo, that person (Hi, ERied) seems to be really experienced when dealing with these machines.
Thanks for sharing it.

Concerning the possible causes for the current leakage:
- Assuming that the bypass capacitor has a large value (like 470uF) and it is electrolytic, yes, leakage can happen any time due to several causes (poor quality, extreme environment storage conditions, long time without being used,...)
- Assuming that there is a diode in parallel with the batteries, if by accident someone installed the batteries with reversed polarity, the diode will do its job by shorting the power supply and draining the batteries capacity very fast. Depending on the diode specs, it may suffer as well.
- Another possibility is that some integrated circuit can be consuming excessive current. Typical candidates are memories (ROM or RAM).
Did you check the machine for good operation at all levels?
At least the self test should pass without failures.

Please share your findings here, and if possible, please post some photos of the internals.
Thank you!

EDIT to add additional detail:
I just remember this old post where we can see some pictures from the internals.
Indeed, the bypass capacitor is hardwired to the battery compartment.
And there is a diode "D6" next to the BT5+ battery lead that can be a good candidate fro checking.