HP Forum Archive 06

[ Return to Index | Top of Index ]

HP 41CV - battery usage Message #1 Posted by Joe Ferguson on 3 Oct 2001, 10:35 a.m. Can anyone tell me why my 41 seems to eat batteries by the bunches. It just started using them at 1 week intervals. thanks joe

Re: HP 41CV - battery usage Message #2 Posted by Vieira, Luiz C. (Brazil) on 3 Oct 2001, 11:09 a.m., in response to message #1 by Joe Ferguson Did it start suddenly? Does it have any modules attached? I have read in many posts that some calcs become battery eaters in many circumstances. One of them is a probable failure in one of the internal components. Older 41's, the fullnut version, having a MBoard with some components, have some electrolytic capacitors that may become unstable and, sometimes, conductive. The newer ones - the halfnut - also have some SMT components that should also be checked. Wait for other posts that would clarify better.

Re: HP 41CV - battery usage Message #3 Posted by Ellis Easley on 3 Oct 2001, 11:36 a.m., in response to message #1 by Joe Ferguson I don't know if this would ever happen to a 41, but my 15C (bought at a sidewalk sale, pretty well scuffed up) would go through batteries in a couple of days. I hooked up an external supply and an mA meter and found that it drew much more current when it was "off" (a couple mA as I recall) than on. I opened it up and found there was a lot of battery corrosion on the PCB. After I cleaned that up, the batteries have lasted for years as they should.

Re: HP 41CV - battery usage Message #4 Posted by David Smith on 3 Oct 2001, 3:50 p.m., in response to message #1 by Joe Ferguson Excessive battery consumption in a '41 is ALMOST always caused by a leaky power supply electrltyic capacitor... the big one in the upper left hand corner of the fullnut CPU card or the middle left side of the half nuts. Also after inserting any module power on the machine to make sure the module has been reset. The time and IR modules in particular need this.

Re: HP 41CV - battery usage Message #5 Posted by Tony Duell (UK) on 3 Oct 2001, 6:19 p.m., in response to message #1 by Joe Ferguson Well, either you're doing something with the HP41 that consumes a lot of power, or there's an electrical leak in the machine. For the former category, the card reader is known for eating batteries (so if you've been reading a lot of cards, expect a short battery life), and the wand takes a fair amount of current. Also, some modules (Time, Card Reader, IR Printer?) can draw a lot of current when first plugged in. It's best to turn the machine on and off again after inserting any plug-in device -- firstly to make sure it's working properly and secondly to 'initialise' it so that it's turned off in the low power state, etc. In the latter category, the leak could be in one of the memory chips (which are powered up all the time the batteries are connected, of course), but more likely it's one of the electrolytic capacitors. That's good because the capacitors are standard parts, the RAMs are HP custom. Open up the HP41 and check the capacitors for electrical leakage (or just replace them). In the older version with the separate logic board the capacitors are on that board, and are the only aluminium electrolytics there. In the halfnut models, they're on the main PCB roughtly behind the 'alpha' key.

Re: HP 41CV - battery usage Message #6 Posted by Joe Ferguson on 3 Oct 2001, 6:38 p.m., in response to message #5 by Tony Duell (UK) OK, I am a novice, how do i open one of these things up!

Re: HP 41CV - battery usage Message #7 Posted by Tony Duell (UK) on 3 Oct 2001, 6:56 p.m., in response to message #6 by Joe Ferguson Take out all the plug-in modules and the battery pack. Peel off the feet. Undo the screws under the feet. Lift off the bottom case (with the flexiprint for the battery terminals and I/O connectors in it). Take off the U-shaped 'centre case' -- make sure you put this back the right way up. In the older type of machine there's a separate circuit board with the chips on that normally just lifts off (but watch out for spacer washers on top of it), but in very early machines there are a couple of nuts holding it down. Remember this is all CMOS circuitry, and that it is _very_ static sensitive. Work on an anti-static workbench if possible, or at least wear one of those grounding straps.

Re: HP 41CV - battery usage Message #8 Posted by Vieira, Luiz C. (Brazil) on 4 Oct 2001, 6:46 p.m., in response to message #6 by Joe Ferguson Just to add: take special care with the buzzer wires; in the halfnut, the buzzer is glued to the botton halfcase and I had once to solder the wires back. The buzzer sound became reduced to less than half (my ears) the original power. No operating failures, just that. I believe static discharge destroyed the cmos output line. So, try not bending them a lot...

Re: HP 41CV - halfnut beeper Message #9 Posted by Tony Duell (UK) on 4 Oct 2001, 7:48 p.m., in response to message #8 by Vieira, Luiz C. (Brazil) Actually, there was an article in Elektor (European electronics magazine) about these piezo buzzers. Apparently they are polarised at the factory by heating them, applying a high voltage (in the kV range) between the terminals, and letting them cool. Re-heating them (e.g. by soldering) can depolarise them, causing the output sound volume to be decuded (apparently, heating one of these buzzers up to boiling water temperature will completely ruin it, and it will make no sound at all untl it's repolarised). I wonder if you overheated the buzzer when soldering the wires back and thus depolarised it.

Re: HP 41CV - halfnut beeper Message #10 Posted by Vieira, Luiz C. (Brazil) on 5 Oct 2001, 6:41 p.m., in response to message #9 by Tony Duell (UK) Hey, Tony; thanks a lot. As it happens with many other contributors, your posts are full of good, useful information. I was not aware of the heat-polarization. That’s quite important knowing about this. But I have soldered the wires at the board, not at the beeper. I also have tried another one, and the low-level sound remained. After all, I sold the unit to someone that would never use the alarm feature (beeper sounds great; maybe alarm frequency is closed to the resonant one). He was aware of that. Anyway, thanks a lot. And I would like to add that I appreciated a lot reading your post describing data flow at the 41´s I/O connectors (answered to Pavel’s request). It was great, and I believe many others have appreciated it.

[ Return to Index | Top of Index ]

Go back to the main exhibit hall