HP-50G Excessive Battery Drain / Fix?

[HrastProgrammer]

Recently I obtained an HP-50G (CNA00...) in perfect physical condition but not 100% perfect functional condition because it drains batteries very fast - brand new Duracells were drained from full to Low Bat in just a week! And that's with mostly sleeping on batteries and on USB when working (checked - USB power works).

Looks like the protective diode has been damaged somehow. I am curious to know if there is any other cause of such behavior? Is this a common fault with HP-50G? This is really a concern to me because I have a chance to buy a few brand new HP-50Gs for a great price locally. I plan to use them to run my HRAST BASIC but if this is a common fault then it doesn't have much sense ...

I will try to power it on rechargeable batteries but I would also like to fix it long-term. I don't have problems with SMD soldering as I've already done some SMD repair work on one of my Alesis Andromeda synthesizers:

Alesis Andromeda A6 ASIC Board Repair

Is there a HP-50G schematics available? I couldn't find any ...

[Tugdual]

The 50g is well known for short battery life and I rapidly purchased low self discharge batteries. Not an ideal solution since the 50g also expects a pretty high voltage. I drained batteries in 3 weeks after acquisition. 1 week is really short time unless you used it intensively. This being said you're the first one suspecting a flaw and I'm curious to see if this leads anywhere. I myself have no clue.

[HrastProgrammer]

(05-27-2015 07:02 AM)Tugdual Wrote:  The 50g is well known for short battery life and I rapidly purchased low self discharge batteries. Not an ideal solution since the 50g also expects a pretty high voltage. I drained batteries in 3 weeks after acquisition. 1 week is really short time unless you used it intensively.

I used it a lot but it was on USB power most of the time. I was aware of big power consumption on 50G but 1 week is too fast drainage ...

[Brian D]

Is is known whether your USB port has enough power available?

[HrastProgrammer]

It's a powered USB port where I usually connect external hard disks, so it has plenty of power available. But let's forget USB ... Should 50G drain all batteries during 7 days @ 2-3 hours work each day (just normal work, no overclocking etc.)? This is not normal.

I have an 12 years old HP-49G+ (CN33... with crappy cash-register keyboard) and 3 batteries (compared to 4 in 50G) last much, much longer. On 50G I expected at least 2 months with average usage, especially because it is powered over USB while connected (during file transfer, for example).

[Marcio]

For a machine as great as the 50g, there should be a low power consumption mode.

[Claudio L.]

(05-27-2015 10:46 AM)HrastProgrammer Wrote:  On 50G I expected at least 2 months with average usage, especially because it is powered over USB while connected (during file transfer, for example).

That's about right. I use it daily at work for the last 9 years and in average I use a set every 2 to 3 months.

[HrastProgrammer]

Thanks! That's what I wanted to know ...

[jebem]

(05-27-2015 05:39 AM)HrastProgrammer Wrote:  Recently I obtained an HP-50G (CNA00...) in perfect physical condition but not 100% perfect functional condition because it drains batteries very fast - brand new Duracells were drained from full to Low Bat in just a week!

Hi,

I would suggest to take readings on yours for comparison. A regular current meter is fine, as long as it can read in the 100mA full scale range.

I took some current consumptions on mine, for reference.
I have used an external power supply consisting of 4 x 1.5V AA LR6 MN1500 alkaline batteries.

Power off state: 0.0mA
Idling current: 12.8mA average.
Pressing keys: small spikes to 55mA.
Doing small calculus: spikes to 65mA.
Self Test: 72mA maximum (65mA average).

Assuming an estimated capacity of just 1800mAh for AA alkaline batteries:
- At 65mA continuous current drain, it should last for 28 hours.
- And at 12.8mA (idling) it should last for at least 140 hours (6 days).

So, using it really heavily (65mA) for only 2 hours per day, it should last for at least 14 days.
But using it lightly each day for the same 2 hours per session, my guess is that it should last easily up to 60 to 70 days (above 2 months).

[HrastProgrammer]

Thank you very much for the reference values, really appreciated!

I measured the following:

Off ... 12mA
Idle ... 24mA
Work ... 65mA

Something is definitely wrong with this calculator because those Off/Idle values are too high ...

[jebem]

(05-27-2015 04:48 PM)HrastProgrammer Wrote:  I measured the following:
Off ... 12mA
Idle ... 24mA
Work ... 65mA

Something is definitely wrong with this calculator because those Off/Idle values are too high ...

Yap, there is a serious issue there.

While I'm not able to supply a schematics, we know that these things uses a capacitor in parallel as well.

Besides the possible protecting diode most probable root cause (I don't know if there is such a protection device installed in the 50G), there is a much smaller possibility that the capacitor may present leaking.

To check for a normal power supply input impedance values:
- Using a wire to short positive and negative terminals in the battery compartment during at least 5 seconds to discharge the capacitor;
- Using a digital multimeter, selecting Ohms auto-range, negative probe to negative terminal and positive probe to positive terminal: initially the reading resistance is very low, but a few seconds later the reading should be above 5MOhm.
- Now, selecting voltage readings in the multimeter, we should read a positive voltage, typically around 0.4V and the value should not decrease with time.

Whatever is the cause, the major issue as I see it, is the fact that to open these machines we need to force the entry, as there are no fixing screws to allow hardware serviceability.
I would return the machine and ask for a refund.

[HrastProgrammer]

Thanks for the suggestions, I will try them ...

I got it for cheap so I will keep it anyway. But, as I wrote in the first post, what concerns me is how something like that could happen and how to prevent such failures with new calculators.

BTW, it looks like 50G has screws beneath the LCD cover so it can be opened much easier than 49G+:

[jebem]

(05-27-2015 05:27 PM)HrastProgrammer Wrote:  Thanks for the suggestions, I will try them ...

I got it for cheap so I will keep it anyway. But, as I wrote in the first post, what concerns me is how something like that could happen and how to prevent such failures with new calculators.

BTW, it looks like 50G has screws beneath the LCD cover so it can be opened much easier than 49G+:

Ah! Yes, I totally forgot about that video! Excellent demo, that person (Hi, ERied) seems to be really experienced when dealing with these machines.
Thanks for sharing it.

Concerning the possible causes for the current leakage:
- Assuming that the bypass capacitor has a large value (like 470uF) and it is electrolytic, yes, leakage can happen any time due to several causes (poor quality, extreme environment storage conditions, long time without being used,...)
- Assuming that there is a diode in parallel with the batteries, if by accident someone installed the batteries with reversed polarity, the diode will do its job by shorting the power supply and draining the batteries capacity very fast. Depending on the diode specs, it may suffer as well.
- Another possibility is that some integrated circuit can be consuming excessive current. Typical candidates are memories (ROM or RAM).
Did you check the machine for good operation at all levels?
At least the self test should pass without failures.

Please share your findings here, and if possible, please post some photos of the internals.
Thank you!

EDIT to add additional detail:
I just remember this old post where we can see some pictures from the internals.
Indeed, the bypass capacitor is hardwired to the battery compartment.
And there is a diode "D6" next to the BT5+ battery lead that can be a good candidate fro checking.

[HrastProgrammer]

Thanks for the additional info!

I probably won't do much about it these days because I have a lot of other things to do. Right now, it was important just to confirm the problem. But I definitely plan to open it and try to fix it someday.

Yes, it works flawlessly, all tests passed, no crashes, etc. Except battery drainage everything else is fine.

[jebem]

(05-27-2015 06:30 PM)HrastProgrammer Wrote:  Thanks for the additional info!

I probably won't do much about it these days because I have a lot of other things to do. Right now, it was important just to confirm the problem. But I definitely plan to open it and try to fix it someday.

Yes, it works flawlessly, all tests passed, no crashes, etc. Except battery drainage everything else is fine.

Another obvious reason to have a current leaking is when batteries have leaked...I had this issue in so many different equipment types that I forgot to mention initially.
When this is the case, usually we can see some fluctuation in the current readings.
And after a few weeks/months when the battery electrolytes finish reacting with the PCB copper traces, usually the machine stops working due to electrical isolation caused by the final chemical reactions.

But of course we need to open the machine to find out.
Good luck with your new acquisition.

Cheers,
Jose

[HrastProgrammer]

(05-27-2015 05:08 PM)jebem Wrote:  To check for a normal power supply input impedance values:
- Using a wire to short positive and negative terminals in the battery compartment during at least 5 seconds to discharge the capacitor;
- Using a digital multimeter, selecting Ohms auto-range, negative probe to negative terminal and positive probe to positive terminal: initially the reading resistance is very low, but a few seconds later the reading should be above 5MOhm.
- Now, selecting voltage readings in the multimeter, we should read a positive voltage, typically around 0.4V and the value should not decrease with time.

I measured it and the resistance stabilized at around 3.8MOhm while the voltage stabilized at around 300mV. There are some small signs what looks like a leakage in the battery compartment but after I opened the calculator I don't see any damage on the PCB, I mean - no traces of leakage on PCB.

Edit: I checked it after a few minutes and it looks like both are still going down ... resistance is at 3MOhm and voltage at 200mV. But, this is to be expected, isn't it?

[jebem]

(05-28-2015 08:35 AM)HrastProgrammer Wrote:  I measured it and the resistance stabilized at around 3.8MOhm while the voltage stabilized at around 300mV. There are some small signs what looks like a leakage in the battery compartment but after I opened the calculator I don't see any damage on the PCB, I mean - no traces of leakage on PCB.

Edit: I checked it after a few minutes and it looks like both are still going down ... resistance is at 3MOhm and voltage at 200mV. But, this is to be expected, isn't it?

Yes, the observed values are normal, but this do not explain your machine current leakage issue.
I was expecting a abnormal behavior here, like reading a very lowish resistance in the order of a few thousand Ohm only, and no capacitor voltage storage at all.
I would interpret your data like This:
Because a multimeter typically applies a voltage under 2V on the porbes when reading resistance, this will not trigger the current leakage observed when you use 6V from the batteries.
Meaning that:
- Most probably the capacitor is OK.
- The Diode should be checked. To do that, it must be removed from the PCB.
Warning: Take great care when desoldering it from the PCB. A small, fine tip, but medium power soldering iron must be used (say, 20Watt).
- While the diode is out, test the machine for current leakage, to confirm thr root cause.
- Just in case of past battery leaking, I would wash the entire PCB using abundant isopropyl alcohol and a soft brush.

- If the above procedures didn't fix the issue, let's not forget the non sense procedure as well: I would reflash the firmware just to make sure the flash rom is ok.

- If nothing resolves the issue, I would say the machine has got an hardware fault inside one of the memory chips.
That explains why a low voltage from the multimeter doesn't trigger the current leakage.

[Frido Bohn]

I am observing this thread with high interest as I had this problem with my HP50g too.
It seemed that the basic current drain at the power-off state added up to the power consumption of the idle- and running-states of the calculator.
Unfortunately, I have not found any satisfying solution until now.

Cheers
Frido

[HrastProgrammer]

I didn't do anything about this because I was here for the last 3 days:



And I am waiting for Nitecore I4 V2 charger and a set of rechargeable batteries to arrive - then I will check the diode ...

[rprosperi]

(06-01-2015 02:54 PM)HrastProgrammer Wrote:  I didn't do anything about this because I was here for the last 3 days:

Very jealous here... I've wanted to attended these, but the closest they come to the NY area usually is Las Vegas. I think this race will be covered on TV here this weekend. Who won?