Zero Point Dual Delay Help

[eshelton]

Voltage at ouput is 5.13.  The two transistors are both BC550's.  The regulator is L78L05. There is no continuity between my output and ground.  I posted a picture earlier in this thread of the pads on the pcb where I get a signal with and audio probe and where there is nothing/radio...that might be helpful (??). 

Thanks for helping!

[RobA]

Voltage at ouput is 5.13. 
...

That's with no signal going in to the pedal and it's volts not millivolts? If so, that seems weird. The output cap's job is to remove DC bias. Either it's not doing it or something is adding voltage to the output.

[eshelton]

Measurement is in volts. I just measured my 9v battery and it is really low (~5.1), so the output pad is receiving the full voltage of the battery. All the wires coming off the board are all f*cked up from messing around with it so much out of its enclosure.  I think I'm going to build a testing rig and pull these wires out of the board. 

C3 is suspect, for sure, but what I don't understand is why I have a ton of dead pads and radio reception all over the right side of the board if its just a bad output cap. 

This pedal is driving me crazy!! 

[RobA]

The far right side of the board is all the digital control circuitry for the PT2399's. I don't know if the noise you are seeing there is an issue or not at this point. I'd focus on the output first. If that were a new battery when you started, I'd suspect that there is a short somewhere. When I saw it was at about half supply on the output pad, that's about what the bias voltage should be, so I figured that pointed at the output cap. Now, with the battery being at 5.1V, I don't know. When you test with a new power source, check what the voltage level is on the output pad.

The 5.1V is possibly point at the voltage regulator. Maybe a short or orientation issue in that are has let the battery drain to the level of the output regulator and then the current draw stopped pulling as much? Could be something or maybe not -- worth looking into though.

I find it far easier to test the boards first with no jacks or switches and sometimes only the leads for the pots. I just hook the stuff up on a bread board for power, jacks and the pots. But, using a test rig is probably a better path.

[eshelton]

Alright, I've got some real weirdness going on here, but I think I've made progress.  Like I said before, there was continuity between the output pad and the 9v (new battery, output pad @ 9v). The output capacitor seemed to be doing its job when I had previously taken it out and measured it while it drained with a multimeter. 

Here's the weird part...There was no continuity between the output and the pads to either side of it. I cut the trace between the output pad and c3, so the output pad should have been completely isolated on the board, but it was still getting 9v!! Wtf? There is a 9v trace that runs by that pad, maybe the trace is touching the pad on the pcb?? I have trouble believing that there could actually be something wrong with the pcb, though. Anyway, I ran my output wire from the leg of c3.  Now the signal is there and the pedal is behaving as it should, BUT it is too quiet. 

I did use 470k for r3 which is supposed to reduce the dry volume, so I think I will change that, but it still seems like it is much too quiet considering I have my amp cranked up pretty high.

[eshelton]

By the way...Huge thanks to you for your help, Rob! 

[eshelton]

Ok I changed r3 to no avail.  The volume is really low and I have to crank my amp.  The signal isn't good and my amp settings don't sound correct.  If I really hammer on the strings I get more volume.  I figured that would point to one of the transistors or the opamp.  The transistors all still look like they're getting good voltage.  But my tl072 looks a little different.  I'm getting:

1 4.03
2 3.67
3 3.96
4 0
5 3.93
6 3.95
7 3.95
8 7.82

Is pin 2 too low? Also, the voltage on this new battery has dropped fairly considerably since I started testing as you can probably see from pin 8. Any ideas?

[RobA]

The battery draining points to a short somewhere for sure. The PT2399's are a relatively high current draw, but that seems to be quite a bit too much to me.

It isn't inconceivable that there is a short in the traces. Check here http://www.madbeanpedals.com/forum/index.php?topic=8451.0. It's likely that these boards are from the supplier at the same time and maybe their line was a bit wonky that day. I haven't seen other reports of there being a problem with any of the DD boards though.

You might be able to see if there is a connection between the output pad and 9V if you look with a magnifier.

I don't have a ZPDD, so I can't give you working voltages on the TL072. Check for continuity around your TL072 with your multimeter for any pins/pads that shouldn't be connected. (By "around" I mean both physically and schematically.)

[eshelton]

I hate to keep reviving this thread...this pedal has been a real paint to debug.  Now I feel like I'm really close but I'm having another strange problem.

When I test the board, it works fine until I turn the mix up and the feedback up and then comes this ridiculous screeching/squealing that does not go away.  Even when I turn the feedback down it is still there.  Oddly enough, the volume of the screech seems to be controlled by the mix knob.

Here's a video...

[eshelton]

Think it may have only been a dying battery! Good noises with a fresh battery so I'm going to play with it a bit more and hopefully everything is good now