Vintage Synth Repair

> Hi Scott:
>
> Thanks for the reply.
> At the moment I’m searching for a complete board but won’t be na easy task…
> On delay algorithms the clicks and pops take the form of repeating patterns
> even without pressing a key.
>
> On smooth short reverbs there’s almost no noise, or none at all.
> On effects like chorus, flanger, pitch shift there’s also a constant white
> noise.
>
> There’s a set of 7 RAM chips associated with each of the DSP chips, but
> unfortunately I don’t have na oscilloscope…
> Those 7 RAM chips are also a hassle to remove because are assembled
> verticaly and the pins are very near from each other.
>
> I also removed the MOD and ESI chips associated with DSP1 and installed
> replaced them on sockets with the ones from the DSP2.
> This didn’t solved the problem.
>
> By now I’m pointing to the DSP or the RAM which are both hard work…
> The DSP chips are common with the SPX900 and with some Yamaha Digital
> mixers.
>
> Best regards.
>
> José
>
> Portugal

I'd guess there's either a bad RAM chip or a shorted or open address or
data line somewhere.  That's sort of good news since the RAM chips are a 
lot easier to find than the DSPs.  An oscilloscope would help to narrow it
down but a logic analyzer would really be necessary to get a solid idea of
what's wrong (i.e. confirm that the data is being read out incorrectly, 
locate the bad chip if they all share the data bus (I'd guess they don't,
it's probably 7x 4 bit wide chips, right?).

But this is beside the point because it will probably be an unreasonable 
amount of effort to repair.

I know the reverb/delay effects in the TG77 really suck, even compared to 
other Yamaha gear that uses the same DSPs.

If you need the effects you'd probably be much better off buying an 
Ensoniq DP/2 or something.
 		 	   		  
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