Archos JBR FM 20 - charge circuit dead?

[scoz]

I think my charge circuit has died, but would like confirmation that the symptoms seem right.

I'm currently using rockbox 2.5 (I think) though unflashed so the original firmware does appear when plugged into the wall and charging alone.

When I plug to charge the Charging screen appears and after about 5 seconds it claims it it fully charged.  The previous time I managed to get it to boot up the battery screen was saying that there was 1.2 volts or so, and the general battery % screen was showing 0.  I also tried plugging in the power supply and nothing happened, it didn't even detect that it was plugged in.  I am also unable to get it to work in USB mode.  I'm sure in the past I've had trouble getting it to go in USB mode, with or without rockbox, when the battery is flat.

I took the battery out and put a multi-meter to it and both sides say 3.7 volts, which is quite a bit more than the 1.2 that the view battery screen was saying but is a reasonable amount less than a full charge.

Does my logic sound right or have I got it wrong?

It's 5 years old now, and many would say just dump it, but I like it and would prefer to keep it, particularly now the wav recording is available.

[dreamlayers]

Dirty battery contacts are a known issue on these, and they could produce symptoms like this.  A defective battery might also behave that way.  A no-load voltage of 3.7 volts doesn't really tell you much.  You need to see how far the voltage drops when there is a load.  (If the contacts are dirty, they are an additional resistance in series with the battery, and that also drops the voltage.)

If the battery cannot supply sufficient power, plugging in the charger might not turn on the device.  It might go in a loop starting to turn on and then turning off, or it might even just click weakly with almost unnoticeable lighting of the power LED on each click.

When I first got mine I jump-started it, providing power in parallel with the battery while the device turned on.   Then it could charge itself normally.

Another thing to watch out for is a bad connection at the charger jack.  It's mounted sideways, and because of that more vulnerable.  Also remember that the device can charge via USB.  If you get it to turn on try holding F1 and plugging in USB.

You can go to the "View battery" debug screen to see what's going on.  If you press up on the screen you'll see real-time information.   There "External" isn't voltage but charging current; divide by 10 and you have your current in milliamps.  Perhaps the simplest diagnostic could be done via that screen.  Plug in the charger and see if "External" and "Battery" voltages go up.  If "Battery" gets to around 4.2 V then the charging circuitry is functioning.

[scoz]

I had taken it apart and the battery contacts looked fine.  I was thinking about updating the hard drive that's why I'd opened it up.

to be honest it's looking like it's dead.  I managed to get something to happen and it said

io4: illInstruc at
000000000

i've managed to get some odd screen up when i plug in the usb, if i hold down f1 I get a screen with

charging 1023
usb         1023
off           variable nos 0 to500 or so
on           1023
key4       variable 0 to 256 or so
key5       variable 0 to 500 or so
vbat       150 to 250
ccharge  variable 0 to 500 or so


that screen seems to run pretty solidly.  

almost got it to boot properly but then it stopped again.  the battery indicator didn't have time to show up though.