Vintage Synth Repair

Hi Hugh,

Here is an update - I have now gotten my scope out and can confirm that on pin 19 of the DAC, on each good voice channel I am getting a waveform. 

But on the three dead channels there is nothing on pin 19..!

Also I have checked the data lines to the DAC's... albeit ten of them on each IC... as I missed pins 11 & 12 (thinking they were just down the one side of the chip!) Either way... all data lines I checked have the square waves present when the key is pressed, on all voices - good or bad!

Therefore would you think I am safe in assuming the BA9221's are bad?

Many thanks for you help by the way..;c)
Cheers,
TOM



--- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian <bouncev@...> wrote:
>
> Quazimodo, how are you doing with the DAC debug, last round of measurement
> questions?
> Hugh
> On Oct 28, 2012 10:55 AM, "Quazimodo" <noddyspuncture@...> wrote:
> 
> > **
> >
> >
> > Thanks Hugh,
> >
> > OK I've uploaded a JPeg of the relevant part of the circuit.
> > I've called it S900_DAC... it's in our photo's section here.
> >
> > So I am getting around 3volts on pins 14 & 19 of the BA9221 (IC107)
> > on faulty voice channels.
> >
> > On good voices there is just millivolts on those pins.
> >
> > Would you suspect the BA9221....?
> >
> > Cheers,
> > TOM
> >
> > --- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian <bouncev@>
> > wrote:
> > >
> > > What pins have the abnormal voltage readings on the 'good' and 'bad'
> > DACs?
> > > Schematic of that area?
> > >
> > > Hopefully this will lead us to figuring out if it is the DACs or some
> > other
> > > part of the circuit.
> > >
> > > OK, Hugh
> > >
> >
> >  
> >
>