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Subject: Re: Maximum DC current in Archos FM?
From: Michael O'Quinn (michael_at_oquinn.info)
Date: 2003-06-29


On Sun, 29 Jun 2003, TP Diffenbach wrote:

>
> Michael,
>
> You're quite right. I shouldn't be doing this. I haven't the knowledge or
> experience. Nor am I insulted; to the contrary, I appreciate your warning. There
> are many many things I'm not competent to do. ;)

Aren't we all? Wisdom is realizing where one is competent, where one
is not, and choosing when to make the "not" become "is".

(Philosophy blog for the day...)

>
> Here's my situation. Having replaced the hard drive in my srchos, I'm getting
> pretty bad battery usage. It's not entirely clear to me what usage I'm getting, as
> I've found that the battery power will drop far enough to turn the unit off, but
> will re-bound when the unit's turned back on.
>
> It also appears to drop when the unit's turned off -- to what the Rockbox software
> calls 35% or so in the first hour after a full charging -- but not to drop furthre
> than about 20%.
>
> Naturally, the archos firmaware and the Rockbox software also disagree --
> substantially -- about the current battery power.
>
> Still, subjectively, I can tell I'm not getting the usage time I had been getting.
>
> Ultimately, my aim is to repair if possible, any drain on my battery.

Well, the first thing I'd try would be to back out the changes as much as
possible. Replace the old drive, and re-solder the joint. Make sure all
the insulating shields are in place, and none or backward (if that's even
possible.)

I would NOT recommend soldering on your Archos unit if this is the first
time. I've been soldering electronics on a regular basis for over 25
years, have replaced some fairly gnarly surface mount components WITHOUT
the proper tools (just basic iron, solder, and flux...) and with all that,
I found soldering on my player one of the most nerve wracking experiences
I've ever had over a tool bench.

>
> My proximate aims are the following:
>
> I want a way of independently testing the batery, without the archos, to confirm
> that it's not the battery that is damaged.

One thing you could do is first charge up the battery, then connect to to
a flashlight bulb with some wires (you might be able to use tape to hold
the wire on the battery) and see how long it lasts. Use a bulb of
appropriate voltage, and you can find it's current rating off the
Internet. If you want to go this route, I'll help you calculate the time
you should see given the bulb's current rating.

DO NOT TRY TO CHARGE THE BATTERY OUTSIDE THE ARCHOS. LiON batteries have
some really specific needs regarding charging, and it can harm the battery
(and maybe even you) to ignore that.

Does anyone with an FM know the voltage reading across a freshly fully
charged FM battery?

Tom, that would be a safe measurement for you to make with a meter -- just
stay away from the current settings.

>
> I want a way to make sure that there are no shorts -- principly, the archos
> harddrive is covered with plastic, presumably to prevent shorts, as the negative
> end of the battery is connected, via the battery access "door", to the back of the
> archos case, which connection would also touch the harddrive were it not for the
> plastic.

I would generally expect a short to either cause the unit (or some part of
it, like maybe one audio channel) to stop functioning altogether, or do
something dramatic like smoke and pop. That said, it could be possible.

>
> In opening the archos, I broke at least one solder point, which I suspect is
> structural rather than electrical. I want to conform this suspicion, by testing if
> any current flows through that solder point.

As bizarre as it may seem, it might be an OPEN rather than a short. If
that solder connection you broke is hindering proper charging, it just
might be the cause. (That's one reason for the battery discharge time
test above, to see if you actually are getting a fully charged battery.)

Sometimes a solder joint can appear to only be structural, but is still
important electrically because it's part of the circuit's ground.

>
> I'd appreciate your thoughts on how I might accomplish these objectives.

Any chance you could take a picture of the joint and stick it somewhere,
so other FM owners could help you out here?

>
> Thanks,
> Tom

Good luck!
Michael



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