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

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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