Zero Point Dual Delay Help

[eshelton]

Hi - Been building more and more pedals and I've been doing well with my troubleshooting but I'm stuck on this ZPDD.  Bypass signal is fine but I'm not getting anything when the effect is switched on.  Power is getting to the board, LED works fine.  I've let it sit for a few weeks since working on it, but I tried several things before giving up for awhile.  I removed the sockets that I had originally put in for the transistors and the regulator (they're all getting power).  Double, triple, quadruple checked the orientation of the ICs, caps, diodes, transistors and regulator. Checked for solder bridges.  Checked offboard wiring connections.  Any help would be hugely appreciated.  I really want to get this thing up and running. 

[eshelton]

Here are some voltage measurements-

battery - 8.63
at +9v board - 8.63
ground @ board - 0

IC1
1 - 4.29
2 - 4.29
3 - 4.27
4 - 0
5 - 4.26
6 - 4.29
7 - 4.29
8 - 8.52

IC2
1 - 4.96
2 - 2.47
3 - 0
4 - 0
5 - 2.84
6 - 2.47
7 - .13
8 - .90
9 - 2.47
10 - 2.48
11 - 2.48
12 - 2.48
13 - 2.48
14 - 2.48
15 - 2.48
16 - 2.48

IC3
1 - 4.96
2 - 2.48
3 - 0
4 - 0
5 - 2.81
6 - 2.48
7 - .12
8 - .89
9 - 2.48
10 - 2.49
11 - 2.49
12 - 2.49
13 - 2.49
14 - 2.49
15 - 2.49
16 - 2.49

Q1 - 2.36, .63, 0
Q2 - 2.37, .63, .06
Reg - 4.95, 0, 8.39

Also, one of the legs of C20 is reading 0v (the leg toward the edge of the pcb).  I took it out b/c I thought it might be the problem.  I tested the cap and it seems to work fine.  Put it back in and it still reads 0. 

[jimilee]

Reflow all of your solder joints and then get an audio probe built and let's see where the signal goes

[eshelton]

Thanks.  I was fairly confident in my soldering coming out of this build.  I did reflow a few questionable connections.  I have an audio probe, but I'm not entirely sure how to use it for this circuit.  I will poke around a bit and post what I find.

[midwayfair]

I'm not entirely sure how to use it for this circuit.

Look up the datasheet for the PT2399 and it explains what each pin does. The pins you're interested in are all on the righthand side of the chip.

You can also use your multimeter to verify that sound is getting to your PT2399s. Probe pin 7 for voltage while playing. It should go to 1-3v.

[eshelton]

Ok I poked around the circuit a bit.  The voltages did read between 3-4 at pin 7 on both of the pt2399 ICs while the guitar was being played.  The audio probe gave me some weird oscillations from the pt2399s. I got nothing from a lot of the connections near the output and none of the ground pads had a signal. Battery got super hot while I was probing. 

Does that provide any clues? Is there a more methodological approach I can take to probing this circuit?

Evan

[twin1965]

Battery got super hot while I was probing. 

Did this happen only whilst probing or also when effect is on?

A hot battery suggests a short somewhere.

[eshelton]

Hmm. I didn't notice it while the effect was on when I tried it previously, but then again I haven't had it on for very long periods of time before disconnecting it since the darn thing doesn't work.  I'll check again for solder bridges.  Damn, I was so confident in my soldering on this board. 

[eshelton]

Ok so I plugged it back in and no hot battery.  I think it may have gotten hot because my un-shielded alligator clips touched when I was probing creating a short.

[eshelton]

Ok so more tests with the audio probe have led me to the C3/R6 area right before the output pad.  The first leg of C3 sounds good.  But the leg that goes to out and R6 is REALLY REALLY quiet.  I can hear it faintly if I really crank my amp. So, what's going on? Is R6 letting the signal go to ground? I measured the resistance with a multimeter and it seems to be showing 6.4kohms, though it should be 10kohms.  I measured the other 10k resistors on the board and 2 others are also measuring between 6.4k-6.6k instead of 10k (R33 and R34). Or maybe C3 is bad??

[jimilee]

You can't measure it while it's soldered in to the board. It will measure incorrectly. You have to remove at least one of the legs.

[Matt]

Ok so more tests with the audio probe have led me to the C3/R6 area right before the output pad.  The first leg of C3 sounds good.  But the leg that goes to out and R6 is REALLY REALLY quiet.  I can hear it faintly if I really crank my amp. So, what's going on? Is R6 letting the signal go to ground? I measured the resistance with a multimeter and it seems to be showing 6.4kohms, though it should be 10kohms.  I measured the other 10k resistors on the board and 2 others are also measuring between 6.4k-6.6k instead of 10k (R33 and R34). Or maybe C3 is bad??

Is their any way your output jack is grounding out?

[jimilee]

You said you check orientation, did you check resistor values? Does it work outside the enclosure jack included?^

[eshelton]

Thanks for the help so far, guys.  The output jack is not grounding out.  The signal at the output is very very faint, nothing at ground.  Also, it seems that at C3 where I am getting the signal it is only the echo, not the picked note.  When I probe the transistor leg closest to the ICs I am getting radio reception through the amp.  That happens for both transistors.  Same symptoms outside the enclosure. 

I will go through and recheck my resistor band values.  That takes me awhile... Any other ideas?

[jimilee]

Did you socket the ic's?