Gareth Magennis wrote in message
...

"N_Cook" wrote in message
...
Gareth Magennis wrote in message
...

"N_Cook" wrote in message
...
No R speaker nor R line out, L &R phones out seem ok, as does the
speakers
on/off sw. Amp hiss from the R speaker only, L is fine.
I got inside this 7 octave thing without breaking any foil ribbons.
The
phones input socket switches seem ok, so does the line out sockets.
But
the
Line-In Left/ Mono input has a bad bypass switch. Although it is in a
position that would suggest a Ring contact it seems to be a tip
contact
switch, difficult to trace the local traces as vias etc.
Anyone know if the problem there would cause the loss of one channel.
As
difficult to "bench test" this sort of item, any other areas to look
at
before some sort of reassembly?



The line outs, phones and power amp are all sourced from the same pair
of
signals, so if the phones work, the problem is from IC1 onwards to the
IC3
power amplifier with regards the speakers, and there is a separate
fault
with the line out. Probably.

Incidentally, there are just two dual op-amps between line ins and line
outs, plus a couple of mute transistors at the line out sockets, so
this
should be trivial to troubleshoot as it doesn't involve the rest of the
keyboard at all.


I have the schematic on pdf I can email you, it is 6.4MB.



Cheers,


Gareth.



I've only run it so far without the keyboard half connected, next time I
come across one I will try external input feeds L & R before
dismantling.
These line in/outs seem to be simple mono so. with tip sw, no ring
contacts
for sensing of R-S connection of a mono jack.
The "switching" logic seems to be if In-L/Mono tip is no longer grounded
then feed that signal to both L & R amps ; if you feed a signal in the R
as
well and so its tip also is no longer grounded then defeat the signal
from
L-in going to the R ch , and allow the R signal to R amp. Or something
like
that, I still don't see why failed tip sw and no signal in there, would
defeat the keyboard output to the R amp.
The phones outputs were only operating as 2 mono outputs, now 2 stereo
outputs from L&R ext inputs . Hopefully that tip sw failure was the
cause
.
I suppose regular repairers of Roland and Yamaha pianos etc have long
frames
that can hold, open, both halves safely while powered up , plus ribbon
extenders.




If you need to play the piano whilst troubleshooting you can use an
external
MIDI keyboard and disconnect and discard the onboard one.
I have in the past used extenders on large modular mixing desks, Lexicon
224's, and built my own extender loom for a Voyetra 8 synth module, but
that's about it.

If there is no sound, you can check the operation or not of the onboard
keyboard by putting an LED in the MIDI out socket and see if it lights
when
you press notes.

I don't know what you are saying about the switching jacks, they are wired
very simply in the traditional manner.
With nothing plugged into the right input jack, the left signal is passed
to
the right via the right switching contacts.
With nothing plugged into the right output, the right signal is connected
to
the left output jack via the right switching contact. (there are mix
resistors just before the jacks).



Gareth.



No change, same loss of one speaker. I'll have to look out for some sort of
basic midi keyboard for the next time, not one of my current bits of test
kit.
No convenient overlay marking of L-out/R-out on the main processor board or
on the PA board. I don't suppose that info of which header/pins those
signals should be on, is out there somewhere. I've found some long P-K bolts
and with spacers should be able to fix the 2 body halves adjascent and 180
degrees apart , and work on powered up , to at least find where those audio
signals lay. This keyboard has been dropped it would seem , stoving in part
of the base chipboard , up against where the ribbons connect to the keyboard
but as the keyboard works as such, then that local area was unaffected , I'm
assuming.
Then hopefully couple some test signals in there without the keyboard
connected