Electric Mistress noise in sweep

[theehman]

Not a DIY project, just a repair.  Trying to get some stuff fixed to sell and clean up around here a bit.  I've got an Electric Mistress V2 that works as it should, for the most part.  The problem is that at a certain point in the sweep, whether in Filter or Sweep mode, there's a very loud static sound.  Adjusting the controls can minimize it but not completely remove it.  All the chips have been swapped with new ones except the 4558.  Any ideas as to what could be causing this and how to minimize it? I also replaced all the electrolytic caps to be on the safe side.

[StephenGiles]

Have you eliminated the voltage dropper as a problem? For starters, I would change the BC 309 and the 741 and see if that makes any difference.

[theehman]

I forgot to mention that the power supply has been replaced with a 12v regulator.

[StephenGiles]

OK I would try powering the unit from batteries, if that doesn't make any difference what is left - the LM339 or the 4013 could be faulty.

[theehman]

I am powering it from batteries.  Both ICs have been replaced.

[jmasciswannabe]

Very interested to see a solution to this one. I have the same issue on two different ADA builds (I've build several others no problem.) Mine is on the upper end of the sweep around 1.7Mhz. Can do the manual thing and isolate it. Sooooo frustrating. Sorry to derail, but I feel your pain!

[StephenGiles]

Which brings me to the SAD1024 - don't tell me, you've already replaced it!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[DrAlx]

You said the controls could minimise it, so am wondering if you can provide info on what combination of controls (in filter matrix mode) maximises it. If you can do that, also measure the clock frequency. In particular, does the static noise increase when color pot is turned to absolute minimum?

[StephenGiles]

Any luck with the noise?