Vintage Synth Repair

My beloved DX5 started some problems...


When I switched it on after few weeks when it was not used, this two  
problems occured, without any obvious reason, and probably not  
connected together:


--------------
Problem 1
All buttons at the left side and under the display don't work. Some of  
them have LEDs lit on. When I change Performances (right side buttons  
work), Voice bank and number buttons LEDs also change (I suppose  
according to programmed data, and because there's just factory setting  
in the memory, they changed in very regular sequential pattern, one by  
on). But I can't change them manually, they don't react.
It occurs with:
+1/Yes, -1/No
2 x 6 buttons: OP Select, OP On/Off
2 x 4 buttons: Bank A, Bank B
2 x 8 buttons under the display: Voice A 1-8, Voice B 1-8


I can enter EDIT mode but all those buttons again don't work. I can  
change only Edit of Function parameters which are selected by  
Performance buttons. Data Entry fader works and can change parameter  
values.


It's not possible to activate Diagnostics (Test) mode because buttons  
which call it don't work.


Problem 2
Instrument plays all sounds (also both sounds in Split or Dual mode)  
with long Release like when Sustain pedal is On. But it is not On. The  
same behavior occurs even with no Sustain pedal connected. When I  
connected the pedal, instrument had no reaction on its position.
--------------


I tried usual stuff - checked and reseated connectors and OS Eproms on  
the main board. It didn't help.


I try to attach to this message one page with schematics of CPC and  
some other boards. Concerning the button control I suspect some  
problem in this circuit.


(Warning! There's a mistake in the description of Push Switch 31 in  
the "LED + Push Switch Table" - it should be only "+1/Yes", not "OP  
SEL".)


Concerning those permanently sounding notes I will check if the  
Sustain pedal jack socket is OK, there's a switching contact inside  
it, maybe it doesn't work properly. It can be only mechanical problem  
(I hope so).


I'd like to ask more experienced electronic gurus here what do you  
think, which component or components would you suspect? And what can  
be reason for such problem, how it could started? Just some old and  
tired component stopped to work? I have no other explanation...


Thanks for any hint or advice.


Daniel Forro