Vintage Synth Repair

Not experienced but I would say that those sound like normal voltagesl.  So
I'd believe the test and look at the physical circuit at those ICs.  If
socketed I would carefully photograph the circuit, static free pull the ICs
out of any sockets and desolder the sockets and put in new ones.  I would
gently reheat solder connections to resistors and caps immediately around
the ICs and replace any transistor.  I am thinking cold solder or
microfracture breaks, failed component but usually not any ceramic caps or
resistors.  I never trust old IC sockets.  I would look closely at any logic
ICs as well.  If your clock is okay and shows up at the chip's IN pin then
its not that.  Its iss rare that the wavetable samples are messed up, unless
someone has had a magnet around.  I'd definitely change the decoupling
electrolytics.   Lorne in Canada

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Royce
Sent: Saturday, February 16, 2013 6:08 AM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Yamaha SY77 faulty

 

  

Any experienced Yamaha techs out there?

The story so far...
I have reseated all of the EPROMs and CPU and all the cable connects.
No leaking Li battery so no board corrosion.

Looking at the DM2 board the supply is 5V02 with digital ground and 12V1 and
-12V2 with analog ground and a line marked MTAG at 14V going to what looks
like a comparator cct outputting a MUTE signal that turns the audio output
off, probably used at power on and off.
There is a 5V and -5V pair of regs (off the +12 and -12V ) on the analog
board buried underneath that I haven't checked.

Only caps on the DM2 board are PS decoupling electros and decoupling
ceramics for the chips and a couple of ceramics for the crystal clock.

On the M3 chips there is a CLKMEL and a CLK3 pin.
The CLK3 is grounded and CLKMEL looks like an FX clock.
A CRO on this and it works on and off during boot then goes off until a note
is played. So I guess the clock oscillator for the M3s are working. I've no
idea about timing though.

The M3 IRQ is open collector and the pullup resistors all look good.
Like the CLKMEL the IRQ line oscillates in bursts which go on and off during
boot and when a key is pressed post boot there is a constant stream at a
varying frequency.

Anyone know what the IRQ error message in the test B means???

Thanks for the help. I could be a bit out of my depth here.

Any pointers would be gratefully received.

All the best
Royce 

--- In vintagesynthrepair@yahoogroups.com
<mailto:vintagesynthrepair%40yahoogroups.com> , "Royce" wrote:
>
> The unit arrived with missing screws in the case. 
> Always a bad sign.
> 
> The service manual, kindly given to me (also the one on the web), is only
71 pages and really only goes through the tests.
> 
> My DX7 and TQ5 service manual are much more detailed.
> Were these synths just 'swap the board" type devices?
> 
> Anyway the test stops at the self test with a message "* M3 IRQ CHECK
ERROR. TEST ABORTED *" and you can't go on to the other tests.
> The service manual only say "If Test B" the M3 test " is NG" no good "then
the error may be related to one of the M3 IC's IRQ levels"
> What does that mean??
> 
> The 2 M3 chips YM7119 are on the DM2 board have something to do with the
Wave ROMs.
> Is this test trying to read all the Wave ROMs and failing?
> Is the CPU just timing out because the M3 isn't returning soon enough?
> It's the interupt request part I don't get.
> 
> Anyone with any more info about this chip?
> Anyone had this problem and managed to get past the IRQ test ?
> 
> I can get a few weird notes out but it sounds like misaddressing of the
Wave ROMs and locks up fairly quickly. 
> 
> Thanks for the help
> Royce
>