Video iPod: USB power is always detected

[dreamlayers]

I'm trying to fix a friend's video iPod which cannot turn off in Rockbox.  If I try to turn it off (pressing the centre and bottom buttons at the same time), it turns off but then the Apple logo appears and Rockbox boots again.  He tells me it used to turn off fine from the Apple firmware, and charging was unreliable or something like that.

Rockbox always shows the plug icon in the status line and the debug screen says "USB pwr: present".  (In Rockbox this seems to come from GPIOL_INPUT_VAL & 0x10.)  Also, after I used disk mode the "OK to disconnect" screen stayed even after I disconnected the USB cable.  I suppose there is some hardware flaw which makes that pin always high.  

Charging using an Apple charger and FireWire cable worked fine, but I have my doubts about USB charging.  I just plugged in the iPod while holding MENU, and Rockbox now does think it's charging, but battery voltage is staying around 4.05 V.  I tried connecting my V2 Archos Recorder to the same USB port and it did actually start charging.  The battery in the iPod is new; my friend replaced it even though I told him I suspected that wasn't the problem.

Right now I suspect that some part of the USB power/charging circuit is damaged.  Does anyone have any idea what part it might be? (I remember that with various Archos devices there were certain parts that would commonly be damaged if the wrong voltage was applied through the charger.)

Edit:  Later my friend reported that the iPod was totally dead and even the FireWire charger did not help.   Upon receiving it, I noted that something was rattling around inside. An inductor to the right of the dock connector (in normal use orientation) broke off.  Near its place there is an indentation on the outer edge of the plastic front which makes me believe this was caused by a drop.  The metal pads on the bottom of the inductor were still soldered to the board.  I found that attempts to tin the thin wires emerging from the inductor just filled the area with flux, but I was able to remove the parts left soldered to the circuit board and resolder them to the inductor.  Then I separated the motherboard from the frame, soldered the inductor, and added a bit of epoxy to help hold the inductor in place.   The iPod now again works as described earlier in the post.  I intend to do additional troubleshooting to try to figure out the USB issue, but I'd first like to understand what circuitry is responsible for it.

Edit2: Later I noticed that another iPod had rubber bits around those inductors.  I'm guessing those rubber bits prevent the hard drive from hitting the inductors.  I asked my friend and he said yes, he remembered opening it up and not knowing where two rubber bits like that go.  Remember, just because a device works without a part doesn't mean that there are no ill effects from leaving that part out.

[Febs]

This doesn't address the entirety of your post, but note that the proper way to turn off the ipod is to hold the play button.

[dreamlayers]

This doesn't address the entirety of your post, but note that the proper way to turn off the ipod is to hold the play button.

Sorry about that, I probably should have read more about how Rockbox is supposed to work on the iPod.  Holding just the play button works much better; the iPod starts turning off sooner and more consistently.  However, I still find that every time after turning off the Apple logo appears again and Rockbox boots again.

[Chronon]

Will it sleep properly from the Apple firmware?

[dreamlayers]

Will it sleep properly from the Apple firmware?

Yes it always sleeps properly from the latest Apple firmware.

Also, the Apple firmware sometimes displays the battery capacity icon, which might mean that it at least sometimes thinks that USB power is not present.  Rockbox always thought USB power was present.  Sometimes the charging icon remains after disconnecting USB but it usually goes away after the iPod goes to sleep and wakes up.  I guess this is not normal behaviour.

[Chronon]

No, it's definitely not normal.