Vintage Synth Repair

Thanks Lorne


> 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.

The M3s are soldered surface mount. Cleaned the tracks
The IRQs seem perfectly good (with a better CRO probe)

>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

Re-soldered the resistors but no luck.

Thanks Lorne
> 
>  
> 
> 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
> >
>