A few weeks ago, my axim X51v started to lose its date and time setting every time I swapped batteries. Being out of warranty, I decided to open it up and investigate.

Getting the axim open is fairly easy; first you remove the stylus, CF and SD cards (or plugs), then remove the four rubber feet (my two top feet had disappeared long ago).

Under the rubber feet are four small Torx (T5) headed screws. Once the screws are removed, the case can be unclipped by inserting a thumb nail up in the middle of each edge then sliding it up and down. Remove the rear part by hinging up from the bottom (the top is hooked over the ear/mic jack socket)




The back-up 'battery' is actually a tiny rechargeable lithium cell (I found this out after I had removed it). I measured the voltage of the cell at less than one volt, it was clearly faulty (A typical lithium cell should be nearer 3v).

[Edit] It's now been pointed out by jballard that it is not rechargeable lithium cell, but is in fact a Panasonic super-cap type EECEN0F204RK However, the replacement lithium cell should be OK

Replacement caps are available from Mouser Electronics (USA) here:
EDLEN204RL3R3S

Farnell (UK) also list the part, but have a ridiculous £16 US stock surcharge !EDLEN204RL3R3S | CORNELL DUBILIER | Capacitors | Passive Components | Farnell

[edit] Good news for us in the UK, Farnell now stock the cap so it can be ordered without the surcharge:
See: Replacing the back-up battery in an Axim X51V




Removing the old cell is a little tricky. You'll need a temperature controlled soldering iron and plenty of patience.

First I removed the solder from the two cell tabs using Solder-Wick (Solderwick is a fine, pure copper, braid coated in a flux that sucks up the molten solder like a sponge). Then, using a scalpel blade gently inserted under each tab while applying heat, I lifted each leg clear of its PCB pad.

The cell is glued or soldered to a pad underneath the cell to to remove it you have to apply heat to the cell's negative tab while lifting the cell with a fine knife blade.
(I said it was tricky )




With the cell removed I decided to check to see if there was any voltage on the cell terminals at the PCB (I had a suspicion that the cell was a rechargeable type because of its tiny size). With the main battery in place, there was 2.8v on the pads.

Unfortunately, the only available replacement I could find, a Varta MC614 SM from one of my regular suppliers, has slightly different tabs.

60614201501 | VARTA | Tagged (PCB Mount) | Batteries & Power Supplies | CPC




I used a small drop of super-glue to hold the cell in place while I soldered the positive tab, then used a loop of tinned-copper wire to make the negative connection.





I gave the cell a few hours to charge before swapping batteries...

This time, the date and time remained correct

Bill

Thanks for the info and pictures. I always thought the x51v had a capacitor for a backup battery.

Nothing is never "no problem".

Interesting, even Dells site lists it as being some kind of capacitor. A small lithium cell would make a bit more sense though and would explain why they are failing...

What markings are there on it?

Thanks Bill!

pencil and paper: n.An archaic information storage and transmission device that works by depositing smears of graphite on bleached wood pulp. More recent developments in paper-based technology include improved ‘write-once’ update devices which use tiny rolling heads similar to mouse balls to deposit colored pigment.

I guess a super-cap would have done the job but, given the small available space inside the Ax (about ~15mm dia x ~3mm deep) , it wouldn't have a much capacity. Panasonic super-caps of that sort of size are 0.1F - 0.22F.

EECS0HD224V. | PANASONIC | Capacitors | Components & Spares | CPC



The Varta cell I used is 1.5mAh which is, very-very approximately, ~3F. I suppose it's possible that the prototype Axims used super-caps and the spec's were not updated.

The cell Dell used is the same physical size as the Varta, but has no obvious markings other than '5D f+' on the tab (which may be obscuring markings on the cell itself).

Bill

I've seen that happen first hand, so it wouldn't surprise me in the least. "Yeah, we started off doing it like that but it didn't work too well so we stopped. Oh, did we forget to tell you about that?"

Thanks for letting us know about this, I've wondered if/where I could get a replacement for that bit if it should ever fail, and it's good to know that I can get it from farnell/cpc if I ever need it.

pencil and paper: n.An archaic information storage and transmission device that works by depositing smears of graphite on bleached wood pulp. More recent developments in paper-based technology include improved ‘write-once’ update devices which use tiny rolling heads similar to mouse balls to deposit colored pigment.

This is a great report. Correction on the part removed. The part that you thought was a lithium battery is actually the Gold cap or super cap. The part is made by Matsushita and the part number is EECEN0F204RK. The capacitance is 0.2F. The spec I have calls it a Electric Double Layer Capacitor EN series. The lithium battery you used as a replacement should work fine. The electrical design is able to use either the super cap or a lithium battery that the x50 used.

Thats a great report?

Guess what there is a capacitor that holds charge for about five minutes in th x51/v, a battery in the x50/xOne is easy to replace,no solder, the other is hard wired to the MOBO.

   

Ah yes, you're right! it's an RK Type. So, it IS a super capacitor after all ! (I'll edit the original piece to avoid future confusion)

As you say, the lithium cell should be happy enough (although it may be a little under-charged at 2.8v)

Incidentally, the trouble with the old one, seems to be excessive self discharge (it's flat from 3.3v in a few tens of seconds - unloaded) so, for some reason it's become leaky.

[stop press]

I've just given the thing a good wash in isopropanol and re-measured it; The self discharge seems to have stopped. So, it looks like contamination around the insulator is enough to bugger them up.

If I get the time, I'll re-fit it into the Axim and see if that's the problem.

Bill

I'm thinking this thread ought to be stickied. Seems like a lot of people posting lately with exactly this problem.

40.8284% - Major Geek

I too vote for Bill Todd to be honoured with a Stickie.

pencil and paper: n.An archaic information storage and transmission device that works by depositing smears of graphite on bleached wood pulp. More recent developments in paper-based technology include improved ‘write-once’ update devices which use tiny rolling heads similar to mouse balls to deposit colored pigment.

My hat is off to you Bill! I've had this problem of having the date and time reset everytime I would swap batteries out for some time now but never had the guts to tinker around in my X51v like I did with my X5. I sort of rely too much on the X51v for my day-to-day activities for me to possibly screw it up and be out a PDA. That's great news that everything is working for you again! Now that I know what I'm up against I may be a little braver to do the surgery.

Well you might not have to do too much tinkering...

I've just measured the Cap I removed from the axim, it still measured ~2v after having sat on my bench for four days. I'm guessing that there's nothing wrong with the capacitor and that the problem is caused by contamination (both on the board and cap). I'll try to make time this afternoon to re-fit the cap into my Axim to test it.

Bill

Happened to me too. I definitely don't won't to open my axim just to fix a problem so small.

Quick update:

I swapped the capacitor back into my axim

Unfortunately when in circuit, the cap discharges rapidly to about 0.9v (after being charged by the main battery). I was unable to remove and re-fit the battery before the clock lost date and time.

It looks like either the cap has dramatically lost capacity, or the clock circuit is presenting a greater than normal load to the back-up supply. Either way, replacing the capacitor with a rechargeable lithium cell seems to solve the problem.

I have re-fitted the Varta cell into my axim.

I'll try to work out a way of measuring the capacity of the original device, as I'd like to know what is the cause of the problem.

Bill

I, too, am having the problem of losing date & time when swapping battery. Probably this is the cause. Now another problem...My x51v will not charge on the cradle & has to be charged by removing the battery & its being charged in the rear slot. Is this possibly related?? I must admit - my Axim suffered water damage & I thought all was lost. But I did get it up & running again. The charging problem cropped up about the same time. So, best guess, could the back-up battery be the cause?