Vintage Synth Repair

I have a Delta that was given me a few years ago and have yet to find the time to fix it.  That said...

It's strange.  That's the VCO output pin of the 74HC4046 and should be a fairly low impedence - meaning that touching it shouldn't affect things so much.  I would expect pins 5 & 6 (capacitor pins) to affect things a good deal more.

From what I can see on the Delta schematics, your replacement KS-196 might not be 100% compatible with the Delta.  Can you tell me what other chips are on the KS-196 board?  If they supply a schematic of their board, please forward it.

--- In vintagesynthrepair@yahoogroups.com, "Quazimodo" <noddyspuncture@...> wrote:
>
> Many thanks for your reply Scott. I think I might have *stumbled* on root of the problem. By no means sorted - because it is a real funny one.
> 
> Here goes...
> 
> As you know I replaced the TOS chip with a 'retro' the KS-196
> 
> Now this retro is a little cct board with three chips on it and long legs that plug into where the original AY chip was.
> 
> One of the chips on this cct board is a 74HC4046 (phase locked loop with VCO) I found that if I touched the chip then the pitch drifted. I could almost 'tune' it by pressing harder, wetting my finger etc.
> 
> So, investigating further I found that if I only touch pin 4 (VCO out) of this IC (using a pin or small screwdriver) - everything is spot on! It just seems to jump to how it all should be. Solid. Now obviously I need to replace me touching it with a better solution, only what!?
> 
> I tried grounding that pin - no. I tried grounding it through a capacitor - no. I am at a loss as, now having found the answer I really don't want to blow anything up with trial and error.
> 
> Could anyone here maybe look at the data sheet for that IC and fathom out why it should behave like this and what needs doing with pin 4?
> 
> I could email the pdf of the chip data or upload intoour files section it here. Please let me know if anyone can help.
> 
> Thanks again,
> TOM
> 
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "Scott" <painintheamp@> wrote:
> >
> > 
> > Hi tom,
> > 
> > If there are any ckts using a bi-polar supply scheme( and part of the ckt you're working on), check to see if theyre where they need to be 
> > 
> > ie; +/- 12 or +/- 15 volts
> >
>