Vintage Synth Repair

Hi Royce,

another detail i may not have mentioned yet is that when powering up the sequencer leds flicker for a shorter or longer period of time. And only during this time slot it is possible to execute an "init ram$" which is part of the hidden functions. Could this be a further hint leading to the cause of the malfunction?

best regards

moe



--- In vintagesynthrepair@yahoogroups.com, "Royce" <rpcfender@...> wrote:
>
> 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
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>