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   Datapack giving a Battery Too Low warning
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barfieldm
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Datapack giving a Battery Too Low warning
« on: Mar 8th, 2004, 8:24am »
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Hi All,
 Just got hold of a 32k datapack, which is in the EPROM eraser as we speak, but reading from it seems to give the Battery Too Low warning even with a fresh battery. It may do it the moment i try to access the pack, or may allow me to use the pack for a couple of minutes first. Is there any known fault with the datapacks that can cause this?
Zac Schroff
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Re: Datapack giving a Battery Too Low warning
« Reply #1 on: Mar 9th, 2004, 2:02am »
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I have never had a pack do that itself; there has always been some other problem for me.  But if a pack is damaged in just the right (wrong?) way...  Does another UVEPROM pack do the same thing?  If not, probably a flaw in the pack (check for obvious damage on the board).
 
A few other ideas, starting from easiest (battery) to harder (peripherals) to bad (internals).
 
Have you chacked the voltage on the battery itself?  I've had them decay in storage (to as low as 6V over a year or so for the cheap general purpose ones), and the Psion will run internally at quite low voltages considering the suggested input of 9V.  If the battery reads less than 8V open circuit, I'd not really consider it 'new' (but checks after my LZ64 declares a battery 'dead' indicate it can tolerate down to just over 6V before it switches off right after power up with a BATTERY TOO LOW message).  
 
Try one of those load test devices Duracell / Eveready sometimes include on their packages...
 
Even read access to UVEPROM packs is fairly heavy power use (flash is usually less; some of the mask ROM program packs are also 'low power', but SRAM packs seem to take the least drain), and anything which might write to one will make the little machines quite power hungry compared to their normal state.
 
Avoid rechargeables; I've seen '9V' rechargeables which read 7.2V once the surface charge is gone, and the good ones seem to be often 8.4V, but they don't hold voltage well under heavy current draw (accessing UVEPROM packs, for example, but particularly writing UVEPROM) and tend to self-discharge rapidly (often 5mAh per day or more, and they are usually only about 120mAh capacity), and often go from 'good' voltage to almost nothing very quickly near the end of the discharge cycle (which could cause data loss, corruption, TRAPs, &c).  
 
Try alkaline batteries instead of general purpose ones; they seem to handle the shifting current demands for non-low-power packs better, and are often rather higher capacity and lower self-discharge rate.
 
Does it do it with an external power supply?
 
Do you also have a Comms Link or other peripheral attached?  These also seem to draw power when the packs are switched on, even if they aren't the active pack.  You'd be surprised how quickly writing data pulled across the comms link to a UVEPROM pack will discharge a new battery.  
 
Now that the easy parts are covered, I *have* had this happen due to a weak connection on the ribbon cable between the two boards.  A check of the board on mine revealed a bad solder connection which was easy to touch up once the board was accessible -- I had probably dropped it too many times.  But since this is real surgery, I'd avoid it until I had no other explanation.
« Last Edit: Mar 9th, 2004, 2:07am by Zac Schroff »

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barfieldm
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Re: Datapack giving a Battery Too Low warning
« Reply #2 on: Mar 9th, 2004, 8:16am »
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Thanks! That has given me some pointers to go on. It doesnt do it with a PSU attached ( i had to create a lead to find out), and tests on my stock of batteries showed the highest of them to be 8.4v, i hadnt tested them before because they are Duracell Procell professional alkalines, and brand new from stock!
 
I havent serviced either the Psion or the pack (apart from erasing the EPROM), but i think i will do this soon, just to eliminate any dry joints, i am a radio engineer and used to dealing with SMT parts, and we have the microscopes etc here at work, so servicing should be quite straightforward.
 
Thanks Again!
barfieldm
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Re: Datapack giving a Battery Too Low warning
« Reply #3 on: Mar 12th, 2004, 11:22am »
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SUCCESS !!!!
 
It turns out that the pack may only have been the instigator of the fault, not really the cause!
 
It seems that D1, the battery input protection diode, was coming to the end of its service life. With the unit running on batteries, it was unable to sink the required current to operate the unit. On a PSU the extra current available allowed the junction to breakdown and supply the needed current. After replacing D1 (an SMT part) with a normal 1N4148 general purpose diode, the unit is once again back up and running and has no problem with the packs!
 
So there we are! If you get a Low battery warning that you just cannot explain, try D1!
 
Incidentally - i am going to try out a method of extending the battery change time limit, and protecting the RAM contents for longer with a low battery - this will use a modern memory backup supercapacitor at 0.1F ! If it works ok, i may supply the caps as a ready to connect kit for anyone who wishes to carry out the mod.
Zac Schroff
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Re: Datapack giving a Battery Too Low warning
« Reply #4 on: Mar 13th, 2004, 12:10am »
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Great job, Martin!  

Tact is for those who are not witty enough to be sarcastic.
thesourcerer
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Re: Datapack giving a Battery Too Low warning
« Reply #5 on: Mar 16th, 2004, 12:08pm »
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Brilliant news. I recently got a batch of LZ64s that had the Low Battery problem, and had been keeping them for spares - but now it looks as though they can be resurrected!  Cheers!
barfieldm
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Re: Datapack giving a Battery Too Low warning
« Reply #6 on: Mar 16th, 2004, 12:26pm »
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Hi, Hope the fix works on your LZs!
 
I only used the 1N4148 diodes because they were to hand and i couldnt be bothered looking for the correct BAS16s in stores.  
For originallity you should fit exact replacements, but the 4148s have a better forward current!  
Theres plenty of space - put 1N4005's in and they will never blow again!!!
« Last Edit: Mar 16th, 2004, 10:32pm by Boris »
logicaid
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Re: Datapack giving a Battery Too Low warning
« Reply #7 on: Aug 19th, 2005, 8:19am »
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It may be a good idea to use a 'schottky' type diode for this since they have about half the voltage drop of ordinary silicon ones, and therefore you just might get a few more hours from your battery before the switch-off voltage is reached. Has anyone got circuit-diagrams of an OrgII? The technical manual on this site mentions various parts by part number, but I haven't found any schematics?
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