Vintage Synth Repair

>
> 
> 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
>

>
> 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
> >
>

>
> 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
> > >
> >
>

>
> Hi Doug,
> 
> Thanks for your reply.
> 
> On the board there are 3 chips, a transistor, a couple of diodes, a zener diode, 4 capacitors and six resistors. It's a very small board - the 3 (socketed) chips are side by side with the other components in and around the IC's.
> 
> As well as the 74HC4046N there is a 74LS93NA and an M086B1.
> 
> There is no circuit diagram but I would think if I removed the IC's I could probably draw it out.
> 
> The pin I mentioned (pin 4) of the 4046 goes to pin 1 of the  74LS93NA
> so touching that pin also 'cures' everything. I suppose that means that the 'touching' symptom could be related to either chip...!?
> 
> The transistor has '2553 5D' written on it.
> 
> Touching most of the other pins affects things to varying degrees - (I can't remember exactly which pins do what and how much) but what is obvious and jumps straight out at you is touching that pin 4 in isolation. Everything just behaves as it was intended. It really is solid... so this retro does actually work (with help), but I haven't a clue what could be causing this and it's doing my head in!
> 
> Today I even tried just soldering a long piece of wire to the pin... which didn't cure the fault in itself but I found that all I had to do was squeeze the wire - just the insulation - and that had the same effect. But I had to squeeze real hard. As you loosen your squeeze the pitch drops!
> 
> I'd really like to get to the bottom of this so any thoughts or suggestions would really be appreciated.
> 
> Cheers,
> TOM
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "Doug" <dougslocum@> wrote:
> >
> > 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
> > > >
> > >
> >
>

>
> thanks for sticking with it, tom, & for returning to tell us what happened. is the korg yours or is this for a client? I think, in the fullness of time, I'd've been inclined to swap out that one chip. this sounds like an output impedance thing, as someone else suggested.
> if the other end of the wire is not attached explicitly to something, then you may find you have drifting pitch again with changes in humidity.... just a thought.
> 
> me, I'd've brought it out onto an insulated metal plate on the panel somewhere & make it a performance controller.... :-)
> 
> duncan.
>

>
> Hi guys,
> 
> Today I fixed the Delta!
> 
> It was a strange fix... and not one I can explain, but my persistence paid off!!!
> 
> The pin I found I needed to physically 'touch' on the retro TOS chip to get the synth to be stable and in-tune... well, the answer was to run a wire, via a 0.1 ceramic capacitor to the casing of an electrolytic on the chorus board. But here's the wierd and really strange thing. The electrolytics used in the Delta are not the kind where the casing is also the negative terminal of the cap. It actually goes nowhere - nowhere else but around the capacitor...!!
> 
> So the casing of this little cap is, apparently a substitute for my body. Result...;c)
> 
> If someone could explain this phenomenon, it would be great. I would be interested.
> 
> But either way I am just glad I found the (or should that be "an") answer.
> Cheers,
> TOM
> 
> 
> 
> 
> 
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "Quazimodo" <noddyspuncture@> wrote:
> >
> > Hi Doug,
> > 
> > Thanks for your reply.
> > 
> > On the board there are 3 chips, a transistor, a couple of diodes, a zener diode, 4 capacitors and six resistors. It's a very small board - the 3 (socketed) chips are side by side with the other components in and around the IC's.
> > 
> > As well as the 74HC4046N there is a 74LS93NA and an M086B1.
> > 
> > There is no circuit diagram but I would think if I removed the IC's I could probably draw it out.
> > 
> > The pin I mentioned (pin 4) of the 4046 goes to pin 1 of the  74LS93NA
> > so touching that pin also 'cures' everything. I suppose that means that the 'touching' symptom could be related to either chip...!?
> > 
> > The transistor has '2553 5D' written on it.
> > 
> > Touching most of the other pins affects things to varying degrees - (I can't remember exactly which pins do what and how much) but what is obvious and jumps straight out at you is touching that pin 4 in isolation. Everything just behaves as it was intended. It really is solid... so this retro does actually work (with help), but I haven't a clue what could be causing this and it's doing my head in!
> > 
> > Today I even tried just soldering a long piece of wire to the pin... which didn't cure the fault in itself but I found that all I had to do was squeeze the wire - just the insulation - and that had the same effect. But I had to squeeze real hard. As you loosen your squeeze the pitch drops!
> > 
> > I'd really like to get to the bottom of this so any thoughts or suggestions would really be appreciated.
> > 
> > Cheers,
> > TOM
> > 
> > 
> > 
> > --- In vintagesynthrepair@yahoogroups.com, "Doug" <dougslocum@> wrote:
> > >
> > > 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
> > > > >
> > > >
> > >
> >
>

>
> Congrats.  Hope your good luck continues.
>