"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.