I am setting up a compac deskpro 4000 and believe that the cmos battery may be in need of replacement. it is the standard button type but it appears to be spot welded in.

how can I test it and what it the best way to replace it ?

Check Chapter 5 from the Service Guides at this link: http://h18000.www1.hp.com/support/techpubs/maintenance_guides/270866-002.html

Section 5.14 in the PDF document says the original lithium battery should not be unsoldered because it may explode. A replacement battery is supposed to be plugged in and a jumper changed. I could not locate a source for a replacement battery.

If You weren't in the UK
I would sasy head down to Radio Shack and grab a AA batt holder
Put two wire ends on it and plug it in..
The Jumper is located next to the pin's for the external Batt.

Consider 3 things:

Make one like the manual replacement assuming it's 3v with a new 3v coin, box and jumper lead/connector
or
Drill through the top layer of the old one and with safety glasses, unsolder it watching the whole time for leakages to mop up and prevent getting onto circuitboard.
or
Solder a couple leads from the connections at the old one to a new 'battery box' (robbed from another defunct board or purchased new) making sure to lift at least one side (contact) from the old battery to take it out of the connection path.

Edit:
Rick,
Good idea! 2AA's = 3v
Enough power to last to the next millenium!!! :)
Rechargeables too if you're fancy ;)

The manual I referenced shows which terminals to connect to and which jumper needs to be changed. It is just not clear what the polarity is, but I would suspect that the darker wire pictured is the negative side.

hi reid,

thanks for the link, most useful.:)

and thanks to all so far for the input.

what I have done is to prise the battery up gently so that I could get at the tags, which I then cut, and battery removed.

I tested this and it was still showing 3 volts, so presumbly not the cause of the initial problem.

the board and battery now had half of the tags remaining, so I soldered 2 peices of wire onto each (observing polarities)

and I'm now back where I started.

the problem with this pc (amongst others) is that if I unplug it, even momentarily it shows errors numbers 162 systems options not set and 163 time and date not set.

the diagnostics and setup are not on hdd but on floppy discs, so I go into setup and setup as required.

apart from no modem (which wouldn't setup, and the CD rom which only works intermittently (mostly not) and possible reason for modem setting up.) the pc runs with no problems whatsoever, and can be booted either warm or cold as many times as you can be bothered to try, is succesful everytime with all options (and time and date set) and no errors.

but unplug for a moment and all is gone, which is why I suspected the cmos battery.

It seems that the battery should be 4.5 volts:
http://www.dsmiller.com/html/Desktop-Cmos-Compaq-Deskpro-4000-5233MMX-B-116.htm
http://www.mobilepower.com.au/au1/m/compaq/deskpro-4000.html

the original is definately marked as 3v its number is ?(pos R) masked by tag. ?R2335.

do you think that the extra 1.5 v's would fry it ?

The battery is likely a CR2335:
http://www.smallbattery.company.org.uk/index.htm?http://www.smallbattery.company.org.uk/sbc_2335.htm

Perhaps you could just wire two 1.5V cells in series, or use a lithium battery and holder as the others suggested. The 4.5V battery assembly looks like the correct one, but I do not know that for sure.

However, if you measured 3V on the battery, I do not know why the BIOS is not holding memory. Is the jumper in the correct position for when the board is using the original battery?

well done reid.


the jumper was across pins 2 & 3 instead of 1 & 2. but those have not been moved. but the situation seems to be cured.

don't know why that was the case, maybe it was used on a network before and needed to be jumpered differently ?

but what puzzles me is why was the bios saved when the pc was switched off ? could it have been powered by static/leakage/feedback, as there was no power from either mains or battery ? it would have had only an earth & negative feed.

I got the CD rom to work long enough to set up the modem, but then it stopped again so I put the old 8x on as a slave and am using that at the moment.

only thing I have now is that I get "Its now safe to switch off your computer" which I didn't get before. I might try running setup again tomorrow.

Originally posted by Vic 970
but what puzzles me is why was the bios saved when the pc was switched off ?Being an older computer, the settings may have been saved in ROM, which does not need power to retain the information: http://www.duxcw.com/faq/cmos/cmos.htm

that doesn't explain why they were lost when the plug was pulled.

and they presumably must be in cmos as it's ok now that the jumper is correctly set.

still :confused: