Pulster fixe(s) and rework
helge.hafting at hist.no
Fri Mar 6 10:22:32 CET 2009
Andy Green wrote:
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> Somebody in the thread at some point said:
> |> I have suggested a refinement on the second approach: short the small
> |> capacitors. Add big caps outside the shielded unit - there are places
> |> with room. But don't put wires from the caps into the shielded
> |> unit. Connect them to the headset plug instead, and break the plug's
> |> normal connection to the circuit board. This approach won't pick up any
> |> more buzz than the headset based solution, or the current bassless
> |> setup. And you can use any headset you want.
> |> The big question is - is it safe to short those small capacitors? Or
> |> will that have other side effects, such as draining the battery or
> |> disturbing sound on the built-in speaker?
> There are a couple of 1K resistors to 0V that will then connect directly
> ~ to the amp outputs all the time before the new DC blocking caps you
> will add back in. But thanks to some recent patches by Mark Brown on
> andy-tracking, we should keep the amp turned off more often.
Can these be safely removed? Are they there just to make sure the
capacitors slowly drain, so you don't get a pop when plugging something in?
Or do they have other purposes as well?
> |> Another question - is a single big capacitor enough, if it is put into
> |> the ground line instead of having one cap for each of the stereo
> |> channels? Or will that wreck stereo sound? One could then use a even
> |> bigger cap.
> You'd need to do both channels; the one with the unchanged cap will
> sound the same as always otherwise.
You misunderstand. I did not propose to do only one channel.
I planned on shorting both the small caps. Then, instead of one big cap
on each of the stereo lines: LEave the stereo lines connected as-is.
Break the ground line (which is common to both channels) and insert a
single big cap there instead. Slightly less work, and perhaps a bigger
capacitor will fit. (It'd probably have to be bigger too, as the two
channels often enough have the same signal.)
> |> There is lots of easily accessible room next to the battery, above the
> |> SIM card.
> | I'd love to see a good answer to those questions. Currently, it's
> | unusable as an MP3 player and that's an important use for me (if
> | I could use it as an MP3 player, I'd carry it with me that much more
> | often, which would in turn increase my use of it).
> Lifting the can and meddling with the caps is nontrivial. Somebody did
> give this plan a go on the list about 6 months ago and reported some
> success though. But I don't recommend considering it unless you are in
> an experimental frame of mind and can deal with the fiddling and risk
I understand that it won't be trivial. Maybe not for me. But if openmoko
creates a standard procedure for this improvement too, then I can have
an electronic repair shop do everything in one go - both buzz and bass
fixes. That will cost me less than having the fixes done separately,
even if both fixes together may cost a bit more than buzz only. I hope
to ship the phone only once, the repair guy will need to open it only
A mass fix will be especially cheap - a good technician doing identical
fixes on a big stack of phones won't need much time on each. It seems
like pulster might set up something like that - but they surely need a
procedure, before they can train someone for the job!
I hope some thought goes into this for the gta03. Sound output from a
phone obviously has low power, but it should be as hi-fi as the sound
chip allows. Ideally, a balanced output that don't use (or need) caps.
One can play uncompressed wav files, and use a high-quality headset or
connect to a regular stereo system. Openmoko could have sound
enthusiast customers, as well as linux enthusiasts.
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