Tutorial: 95LX: Fix "Low Battery" fault

95LX user Robert Rozee from Christchurch, New Zealand, provided info on how to fix the common fault that the 95LX reports "low battery" although the inserted batteries are fresh and full:

See also: Tutorial: Disassembly of a 200LX (disassembly of a 95LX is very similar, but be careful, as some details are different)

Hi,
    I've just spent the evening fixing the 'Low Battery' fault on an
HP-95LX a friend gave me last week. Your website
(www.daniel-hertrich.de/95lx/) provided invaluable information - the
photos showed me the polarity of some components I had removed without
taking note of the polarity  :-) 

I've searched the web a bit about the 'Low Battery' fault that seems to
eventually plague most 95LX's, and the only clue as to a repair I found
was a guy who said his unit came back with a note about replacing a
capacitor. After quite a bit of experimentation - removing and replacing
small tantalum capacitors - I now know which one... I thought you might
like to add the information to your website.

The offending capacitor is a 0.1uF tantalum device located just above
the blue resistor pack that is to the right of the lower RAM chip (and
to the left of the keyboard connector). It is visible in this photo:


The capacitor is the yellow part (I'm not sure how electronically savvy
you are!)

Removing the capacitor, and the 'Low Battery' messages go away and the
'battery meter' in setup shows full. Replace it, and the messages
returns when powering up and the battery meter reads empty. Pretty
conclusive. In my unit I replaced the device with a 0.1uF chip ceramic
capacitor, but I suspect that it could simply be left out without much
problem.


Hopefully this info can help some other old calculator collectors out
there - it's a pity no one found the solution back in the 90's!!

---

Attached are a couple of
photos of my HP95: one before the component was replaced, with an arrow
pointing to it; the other after it was replaced, with a red mark on the
body of the new capacitor.

I just grabbed a ceramic capacitor of the right value out of our parts
store here at work, but a suitable component would be:

Kemet C0805F104K5RAC
http://nz.farnell.com/jsp/search/productdetail.jsp?SKU=1288272
The only important details are 0.1uF and small enough to fit. The old
component is polarized (the end with the bar is POSITIVE), while the
replacement (ceramic) part is not. Note that this is a suitable
replacement ONLY for this one tantalum capacitor - I tried replacing
them all and got into a right pickle! (this is where the photos on your
site saved me)

Before:


After: