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Subject: RE: Help!!! JBFMR20 -error showing USB mode
From: [IDC]Dragon (
Date: 2004-08-10

Hmm, how about these:

- if you have a multimeter, check if the voltage on the USB jack at the pin
where +5V would be provided by the PC is moving when you press keys. It is
one of the outer pins, the other one is Gnd (connected to the chassis).
- clean the PCB with alcohol (using e.g. Q-Tips and compressed air)
- if nothing helps, add a pulldown resistor to the +5V USB pin to make it
harder for false alerts

I'm not sure if the circuit allows to influence or measure it there. If a
diode is inbetween, you have to go futher towards the CPU.


> That is possible I suppose! That sounds a bit daunting, but I will try
> opening and seeing if anything is obviously wrong! Are there any tips
> you can offer?
> Thanks
> -----Original Message-----
> From: [IDC]Dragon []
> Sent: 10 August 2004 15:11
> To:; Rockbox development
> Subject: Re: Help!!! JBFMR20 -error showing USB mode
> > A message I sent earlier is below, but this is now happening with
> > virtually
> > every button I press - can anyone help?!!!
> >
> > Thanks!
> >
> > I'm using a daily build, having succesfully flashed my firmware, but
> from
> > time to time I keep getting the USB logo on screen in response to me
> > pressing, for example, the up key.
> >
> > I'll install the latest daily build, but has anyone else had this and
> what
> > is the solution?!!!
> I'm confident this is a hardware problem. The USB plug is detected by one
> of
> the analog inputs the CPU provides, the keys are done by two other analog
> channels. Somehow your box seems to have crosstalk between those. Not much
> I
> can advise for, except to open it up and check for bad soldering or
> shorts.
> Maybe some humidity went in?
> Jörg

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Page was last modified "Jan 10 2012" The Rockbox Crew