Vintage Synth Repair

Hi moe

> removed the DM2-board and - as you predicted - the SY77 can be used as midi-controller. But even while the DM2-board is removed it freezes when one of the "MODE" is pressed. So I assume that the malfunction is caused by somewhere on the DM1-board, right?

Maybe. Both the switches/leds, foot switches and the keyboard are scanned and controlled by a separate micro-controller (IC137 on the circuit diagram). 
Do you have the cct diag?
If there was a problem there is is likely that it would appear in more that one switch.
Do you see the failure in different switches or in a complete block?

Freezing is usually caused by the CPU going into a loop, either software or hardware.

The hardware freeze can be caused by the 2 interrupt requests(IRQ), the nonmaskable interrupt(NMI), the reset(RES) or the Standby(STBY) pin's state being held.
IC101, the CPU, has a NMI and STDY that are never used .
The RES is only controlled when the unit powers up.
Both the INTs are attached to the M3 chips on the DM2 board.

So my guess is when you press the Mode buttons the CPU makes a request to the M3 chips (no longer connected) and waits in a software loop for the reply.

So from this long winded reply I would guess that the DM1 board could still be OK. (I would have to pull my SY77 apart to be sure)

> Could you tell me which parts are the high-speed-buffers you mentioned and how to test them?

The buffers are on the DM2 board so you will need to reconnect it.
IC201 is the 'control' buffer and has the chip selects(CS), marked as FMSEL, M3PCM and M3FM  on it.
IC203 is the CPU data buffer
IC202 is the CPU data addressing buffer.

These are very fast buffers and you will need a good oscilloscope to read them without loading the pins.

The IRQs are unbuffered so put a oscilloscope on it and make sure you can see a pulse to ground. If it is held to ground then the CPU will be hardware frozen.

Of course the easiest way is to persuade a friend to let you try out your DM2 card in their SY77 (could be the same board in a TG77 ??) and then put his DM2 board in your synth to start to pin point the problem.

I tried to find a spare DM2 board from Yamaha, but I ended up buying another part broken SY77 and swapping parts around to make one good synth.

So if you find a source of DM2 boards let me know so I can get this other one going.

I am in Melbourne Australia. If you are close, feel free to email me.

Best of luck
Royce
 
> thanks a lot and best regards
> 
> moe
> 
> --- In vintagesynthrepair@yahoogroups.com, "Royce" <rpcfender@> wrote:
> >
> > Hi moe
> > thought you would have, just a good place to start.
> > 
> > There are two main boards in the unit. You can disconnect DM2 (the sound generating board with the 2 M3 chips on it) from the main controller DM1 board by unplugging the ribbon cable.
> > 
> > You should be able to power on the unit and play it as a Midi controller if the DM1 board is OK.
> > 
> > If you can, then look at the DM2 board.
> > The DM2 to DM1 connection is mainly buffered so have a look on the output side of these high speed buffers.
> > 
> > The M3 chips can hold the CPU interrupt low and so freeze the unit and this is where I would look first. 
> > 
> > It turned out that that on  mine, although I can get mine to at least display a M3 interrupt fail on the first test, was a failed M3 chip.
> > 
> > 
> > All the best
> > Royce
> > 
> > 
> > --- In vintagesynthrepair@yahoogroups.com, "m.sislack" <m.sislack@> wrote:
> > >
> > > Hi Royce,
> > > 
> > > of course i have but even when i try to enter the diagnostic mode it freezes immediately.
> > > 
> > > Thanks for your suggestion anyway
> > > 
> > > moe
> > > 
> > > --- In vintagesynthrepair@yahoogroups.com, "Royce" <rpcfender@> wrote:
> > > >
> > > > Hi Moe
> > > > have you tried the diagnostics?
> > > > 
> > > > Press and hold VOICE
> > > > Press and hold BANK D
> > > > Press 8
> > > > 
> > > > All the best
> > > > Royce
> > > > 
> > > > --- In vintagesynthrepair@yahoogroups.com, "m.sislack" <m.sislack@> wrote:
> > > > >
> > > > > Hi Paul, 
> > > > > 
> > > > > thanks for your quick reply. The CR2032 has already been changed, all parts, boards, ics and cables i have dis- and then reassembled and reseated, I also replaced all of the electrolytc capacitors on the mainboard, but the problem still persists...
> > > > > 
> > > > > regards  moe
> > > > > 
> > > > > --- In vintagesynthrepair@yahoogroups.com, Paul Krull <paul.krull@> wrote:
> > > > > >
> > > > > > Â You may need to replace the CR2032 batteries and reinitialize the SY77. A cable or chip could be unseated too.
> > > > > > Â  Â Thanks
> > > > > > 
> > > > > > 
> > > > > > ________________________________
> > > > > >  From: m.sislack <m.sislack@>
> > > > > > To: vintagesynthrepair@yahoogroups.com 
> > > > > > Sent: Sunday, June 9, 2013 8:27 AM
> > > > > > Subject: [vintagesynthrepair] YAMAHA SY77 freezes
> > > > > >  
> > > > > > 
> > > > > > 
> > > > > > Â  
> > > > > > Hello everybody,
> > > > > > 
> > > > > > I´m trying to repair an SY77, that when I got it was stuck in untility-mode. It freezes when one of the "mode"-buttons is pressed, so I cannot even enter the test-mode. Furthermore the wheels dont´t have any effect on the sound, but send midi-data. Anyone who experienced an similar problem or could provide any suggestions?
> > > > > > 
> > > > > > best regards
> > > > > > 
> > > > > > moe
> > > > > >
> > > > >
> > > >
> > >
> >
>