Zero Point SDX help (please) SOLVED !!!

[madbean]

Resistor values around the PT2399s look good from what I can see. I'll second Jon on the audio probe. It's going to be necessary in this case. Your voltages seem okay and your components appear alright (not that I've looked at every resistor value in your build).

You need to audio probe: R8, R9/R10 junction, R11/R12 junction and R21. Do this with the Ghost switch off and using the Feedback knob all the down and then a little bit up.

[pierre67]

  sorry...I did not know what an audio probe was...all this years building effects, I guess I was just lucky...
Right now I'm reading RG's article on how to make (and use!) a probe.

I checked all resistors, nothing wrong here. I know that it is difficult to check a resistor value that's allready soldered in a circuit, but having another ZP working helped me to compare...I usually check all resistors with a multimeter before solder...the same with caps, so I was pretty sure that the problem wasn't there.

[pierre67]

thanks for your replies, I will check with an audio probe as soon as I build one and learn how to use it...
Just one detail :I have soldered a on-off-on switch for  "ghost" ...but I guess that that is not the source of the problem.

[pierre67]

So...
I put together a probe and I have done some testing...
With fdbk all the way down and delay and mix pot at noon, no ghost, mod and path engaged...

R8 : (C4 side) clean dry signal, (R41 side) mute
R21:(C29 side) Faint delay signal, (Out side) mute
R12: (C10 side) faint delay signal, (IC2 side) normal? Delay signal
R11: (C10 side) faint delay signal, (IC2 side) mute
R10: (C5 side) mute, (IC2 side) dry signal
R9: mute in both sides
R18: (C16 side) faint fuzzy signal, (IC3 side) distorted gated delay signal
R17: (R14 side) faint fuzzy signal, (IC3 side) muted (i guess, I forgot to note this one )
R16 : (IC3 side) delay signal
R15: (IC3 side) mute

...sides are taken from the layout. Not sure if I'm doing this right, In any case I'll do some more testing tomorrow...
Thank you !

[wgc]

yes, r45 is omitted as noted in ZPSDX documentation update...
I'm checking resistors values one by one, but still not finding the source of this problem...

It jumped out at me right away so I suspected it might be by intent, but figured i should mention it just in case..!

Those are nice pics btw... I'm sure you'll figure it out soon

[madbean]

The problem seems to center around R8/R41/R22/R9/R10.

Try this: remove both PT2399s again. Now audio probe pin 16 only of IC2. Do you get a strong clean signal there?

If so, can we see a pic of the bottom of the PCB on the area directly beneath IC2?

[pierre67]

hi !
Removing both IC2 and IC3 I don't hear any signal at IC2 's pin 16...mute. With only IC2 removed I get clean signal in pin 16...
I don't know if this can help but I'm posting some pictures from the solder side...do I have to de-solder the delay pot to show a clearer view?





...looks messy but its only the flux...
Again, thank you for your patience...

[madbean]

Well, that's pretty bizarre. With IC2 removed you should get clean signal at pin16. You are getting that, so good. But, you said removing both IC2 and IC3 you get no signal at pin16 of IC2. Frankly, I don't know how that is possible. removing IC3 should not effect the path of the clean signal in any way.

I'll have to think so more about this.

[pierre67]

I'll check again...

[pierre67]

... sorry...with IC2 and IC3 both removed I get clean dry signal in IC2 pin 16...and mute in pin 16 IC3...In fact I get clean dry signal in IC2 pin 16 with or without IC3 installed

[madbean]

Okay, that's what I suspected. That's exactly how it should be.

[pierre67]

I have done some more testing...change all ICs and transistors and the problem still there...
One thing that I've noticed is that the feedback pot goes from 1 dirty repeat when is full turned off to self feedback (I really don't know how to put it in words) when I turn it just a little (like at 9:00)...more exaggerated when ghost is on...I should post some sound samples but right now it's a little complicated...
Next thing I'll do is take off Delay and Fdbk pots to change some caps...I don't know, I'm lost here

[midwayfair]

I have done some more testing...change all ICs and transistors and the problem still there...
One thing that I've noticed is that the feedback pot goes from 1 dirty repeat when is full turned off to self feedback (I really don't know how to put it in words) when I turn it just a little (like at 9:00)...more exaggerated when ghost is on...I should post some sound samples but right now it's a little complicated...
Next thing I'll do is take off Delay and Fdbk pots to change some caps...I don't know, I'm lost here

I think you need to check that your feedback pot isn't a 1M ... is your modulation working properly?

[pierre67]

...no, my fdbk pot is a 50Kb...and yes, modulation is working...rate led blinks and all... with the mod switch engaged  the distorted motorboarding noise gets some sort of modulation, that varies as I turn rate and depth pots...After checking all resistors values and looking for shorts and solder bridges I think I have 2 things left to check...all caps and diodes. I have changed some electrolytic and those 10µF tantalum, just to see if the problem was there, I guess I have to remove pots to test the rest of the caps...I don't know how to check for the diodes, they are all 1n914.
Right now I'm comparing values with diodes installed in the working ZPSDX...all of them are around 0.560v in my multimeter...don't see anything strange here...

[pierre67]

...et voilà !!!
Yesterday evening I took all pots off to see if I could find something and nothing...so I decided to desolder every electrolytic , diode, and check again all the rest of the caps...Today, after work I found the problem : I put a 10nF in place of a 100nF for C26...
I feel super stupid and happy at the same time...It took me only 30 minutes to put all together...and voilà : my second Zero Point SDX works and sounds as good or better than the first one !!!

Thank you for your help,

Pierre