I the past I recall many discussions about blowing the output protection FETs on
the Audio I/O board. I think it was possible to fry them if you plugged in the
cable to the K2500 output when it was already connected at the other end.
Perhaps it was static zap or some grounding problem. Anyway, the headphone
output has no such protection. It would seem strange though that ALL the outputs
would go bad together since each output has a separate protection FET.

Looking at the schematics, there is a control line coming in on the Audio board
connector at pin 1 which is called UNMUTE. From the circuit it would appear that
this signal would have to go negative with respect to ground to turn off those
FET's. They need to be turned off in normal (unmuted) operation. So perhaps that
signal is not getting there correctly.

If your electronic guy is capable of getting inside (Keyboards are a bit tricky,
but there is documentation on how to open them up), and if he could use a scope
to take a look at the signal coming in on the audio I/O board connector pin 1,
which then goes thru diode D9 to pull down the gates on those fets, then maybe
you could find out what is happening. Also, the audio signal for A LEFT comes in
one side of a 620 ohm resistor (R1). The FET is on the other side of that
resistor. If the audio signal looks good on the one side of R1, but looks nearly
shorted on the FET side of R1, then you might try just removing the FET
temporarily to see if the A Left output now seem normal. All that would confirm
that its the FET's killing the signals. However, the cause is more likely the
UNMUTE signal since it would affect all the outputs as you have described.

Hope this gives some clues and helps.

-John

----- Original Message -----
From: dr_orient
To: KurzList@yahoogroups.com
Sent: Friday, January 09, 2009 8:51 PM
Subject: [KL] K2500 Output Schizophrenia


Some background: I've got KDFX, max P-RAM, all ROM options(Piano,
Orchestral, and Contemporary), and max sample RAM on my dear 2500.
OK, here's my problem: I get perfectly good sound from my Headphone
output, but from zilch-5% or so (distorted at that) from everything
else - Mix, A-D outs, you get the picture. Anybody have an idea (or
suggestion) as to what gives? My main electronic guy is fairly
baffled, which for me is a scary thing, since he's seen almost
everything that can happen to most electronic instruments.

I know enough to know I'm way out of my league here in terms of
technical knowledge (I'm just your ordinary musician). Do I just bite
the bullet and send my baby off to Uncle Sweetwater? Last time I did
that, it was gone for over a month, but it's been over a month as is
and I haven't found a solution to my little quandary.

Anyone with insight into the Tech Gods willing to speculate? All
assistance gratefully appreciated!

All The Best,
The Dr_





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