Vintage Synth Repair

Hello:
I'm having problems with the effects section on the SY99.
When the SY99 is switched on, it makes a great noise and high level distortion.
The noise is coming just from the effects section 1.
It's a sort of pops and crackles and zzzz which varies with the effect selection and don't even need to press a key to start making the noises.
Checked for bad solder joints, cleaned the plugs and sockets and replaced the internal battery on DM2 internal board.
Problem isn't solved...
If the effects bypass switch is pressed the sounds are clean.
At the moment I'm searching for a second hand DM2 board (P/N VK287500) or alternatively the DSP1 chip (P/N XF164A00, Ref.YM6007).
Any help will be appreciated!
Best regards.
José
Portugal

> Hello:
> I'm having problems with the effects section on the SY99.
> When the SY99 is switched on, it makes a great noise and high level distortion.
> The noise is coming just from the effects section 1.
> It's a sort of pops and crackles and zzzz which varies with the effect selection and don't even need to press a key to start making the noises.
> Checked for bad solder joints, cleaned the plugs and sockets and replaced the internal battery on DM2 internal board.
> Problem isn't solved...
> If the effects bypass switch is pressed the sounds are clean.
> At the moment I'm searching for a second hand DM2 board (P/N VK287500) or alternatively the DSP1 chip (P/N XF164A00, Ref.YM6007).
> Any help will be appreciated!
>
> Best regards.
> José
> Portugal

Could be a bad RAM chip or a short somewhere.  I don't recommend putting a great deal of work into it if you can't just replace the entire board.  A replacement DSP will be very hard to find and soldering it in won't be easy either.  How does it sound on a delay algorithm (longest delay time, no feedback, no input sound)?  Is it a repeating pattern of clicks and pops, or constant white noise?  Does it pass any audio (effect processor 100% wet)?  Is it distorted?  You can find the RAM chip associated with that DSP, look up the datasheet and use an oscilloscope to see if there are stuck address or data lines.  If there's an identical working effect processor, you can compare it to that.

I think the SY99's effect chips (if not software effects algorithms) were used in other boxes, SPX900 maybe?  But decent (even much better) effect processors aren't expensive or hard to find, so it may make more sense to just use something else.

I have a TG77, I know it has 4 independent chips for effects (I think 2 from the SPX90 and 2 from the EMP700), but I understand that the SY99 has upgraded effects and I'm not sure how they differ.  At least on the TG77 I believe the individual chips work totally independently with a program loaded from the CPU.
 		 	   		  
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> 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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