HP Forum Archive 06

[ Return to Index | Top of Index ]

Changing 42S batteries Message #1 Posted by Dan on 13 Aug 2001, 4:56 p.m. My 42S _always_ loses its memory when I change its batteries. So I was wondering, does the 42S have a super-low-power mode analogous to the 48's coma mode? If so, how would I enable it? Dan

Re: Changing 42S batteries Message #2 Posted by Andrés C. Rodríguez (Argentina) on 13 Aug 2001, 5:09 p.m., in response to message #1 by Dan It should be enough to change the batteries rapidly, also plan to change them before they get too low. Just in case, there is a "coma" mode, invoked by a three key sequence, I am not sure what the sequence was, but if you search previous postings here at the Museum (including Archives for the last years) you will find a posting describing it.

Re: Changing 42S batteries Message #3 Posted by Paul Brogger on 14 Aug 2001, 10:46 a.m., in response to message #1 by Dan I seem to remember another post by a more knowledgeable participant on this subject. If I remember correctly, it's a capacitor that has failed. I think at least one of it's functions is to maintain voltage during battery changes, and if it can't store charge, the voltage falls with battery removal. Maybe someone else can supply the capacitor's characteristics -- I suppose it could be replaced if a suitable equivalent were found.

Re: Changing 42S batteries Message #4 Posted by Tony Duell on 14 Aug 2001, 1:48 p.m., in response to message #3 by Paul Brogger I was going to suggest replacing the backup capacitor. The problem with doing so, of course is that you have to open up the 42S, which is not that easy. The capacitor in question is a 100uF 10V surface mount part connected across the battery connections (via PCB tracks) and it's the largest capacitor on the PCB. It's not hard to find. Nor is it hard to get a replacement -- it's a standard part. RS components/Electromail sell them in the UK (the only problem being you have to buy 10). If you're used to doing SMD rework, it's easy to change as well.. Oh yes, don't take the 10V rating too seriously -- some machines have a 6.3V one. Anything greater than the battery voltage is fine (provided it'll fit in the case) -- 10V is the easiest one to find in my experience. I've also known this capacitor become leaky and drain the batteries quickly -- something to check if you have that fault.

Re: Changing 42S batteries Message #5 Posted by W. Bruce Maguire II on 14 Aug 2001, 12:36 p.m., in response to message #1 by Dan I know it is a clumsy, kludgy approach, but maybe you could hook some small clips to the battery terminals and supply a parallel voltage source during the battery-change. I've never tried this, but engineers always gravitate toward redundancy... Bruce.

[ Return to Index | Top of Index ]

Go back to the main exhibit hall