Sharp EL-5100S - Battery Drain

[acg]

I have a Sharp EL-5100S in generally great condition (display, case, etc.), but the batteries drain very quickly, in about a month. I do not see any obvious issues internally, but I am not an engineer.

I have another EL-5100S and the batteries last a pretty long time.

I'd appreciate any suggestions!

Thanks!
Anthony

[Jeff_Birt]

There is not much inside these, a processor and 3 LCD drivers plus a handful of caps, resistors, etc. The first thing I would suspect is a little conductive gunk on the PCB where the batteries are. Coin cells do sometimes leak, though typically not much so it might not be obvious at first. Clean that area up with alcohol.

I've attached a picture of the power supply section. The 100pf cap is across the battery at all times. If this is leaking (become slightly conductive, not physically leak) it could drain the battery. Ceramic caps typically are not an issue but they can short circuit internally so it stands to reason that one could become slightly conductive.

   

[Dave Britten]

I have a PC-1211 that exhibits similar symptoms, so I should probably go on a gunk hunt too.

[Jeff_Birt]

(04-10-2023 06:09 PM)Dave Britten Wrote:  I have a PC-1211 that exhibits similar symptoms, so I should probably go on a gunk hunt too.

You mentioning the 1211 reminded me of something. The EL5100S service manual mentioned that on early units a small PCB was bodged in to fix some sort of bug in one of the chips (don't remember which). On later units this the chip was updated to correct the problem. This bodge added 1-2 other small ICs which could be a source of problems too.

The early 1211s had a similar bodge board which was mounted in the lower left corner when viewed from the back.

[acg]

Thanks!
I'll give cleaning the battery area a try and cross my fingers that's the fix.
If not, I may have to enlist a friend on the capacitor.
Thanks again!