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.
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.
Reflow all of your solder joints and then get an audio probe built and let's see where the signal goes
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.
Quote from: eshelton on July 22, 2013, 09:20:34 PMI'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.
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
Quote from: eshelton on July 22, 2013, 10:28:31 PM
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.
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.
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.
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?????
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.
Quote from: eshelton on July 23, 2013, 07:42:24 PM
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?
You said you check orientation, did you check resistor values? Does it work outside the enclosure jack included?^
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?
Did you socket the ic's?
yeah, all 3 are socketed. voltages are in an earlier post.
Yeah I saw the voltages. It sounds as if there is a hardware problem somewhere. I had an issue with a pin being bent on an ic socket of the zpsdx. This problem is most perplexing for sure.
Resistor band values are all correct. IC socket pins all appear to be coming through the board and soldered in place. Should I try taking them out and soldering the ICs directly to the board? But would the voltages show up apparently correct if there were a problem with the socket?
I'm going to do some extensive and methodological probing and voltage testing and I will post my results.
I'm not sure At this point but you have voltages so tht wouldn't be necessary. If midwayfair or scruffie or josh could have a look and see what's next, that'd be cool.
Ok, here is the result of some audio probing. Blue dots are a good signal. Pink R's are radio reception. No dot means nothing is coming through there. And I have already mentioned the very weak signal after C3.
Checking C3, R6 and the out for partial bridges, or for bad joints would be good. Replacing C3 might also help.
Jacob
Thanks, I've checked those pads for bridges and reflowed with no luck. I don't have a replacement for c3 laying around, but I will replace it as a last resort...I'd just have to make a trip up to the electronics store tomorrow probably. Any ideas that would explain all the dead pads and radio interference on the right side of the board?
Quote from: eshelton on July 24, 2013, 10:56:07 PM
Thanks, I've checked those pads for bridges and reflowed with no luck. I don't have a replacement for c3 laying around, but I will replace it as a last resort...I'd just have to make a trip up to the electronics store tomorrow probably. Any ideas that would explain all the dead pads and radio interference on the right side of the board?
Usually radio interference is a lack of ground somewhere.
It wouldn't have anything to do with leaving out r30, would it? That's what was recommended in the build guide. Maybe need to jumper or something to connect that ground pad? Idk.
Quote from: eshelton on July 24, 2013, 11:48:47 PM
It wouldn't have anything to do with leaving out r30, would it? That's what was recommended in the build guide. Maybe need to jumper or something to connect that ground pad? Idk.
Nope, that's for delay times, no need to socket it.
Do you get any sound if you remove the 2399's (IC2 and 3)? Have you any others to put in their place? I experienced this with the neptune delay I built. You can get bad ones from time to time. I got a bad one from mouser ironically. I really think this a bad part issue.Your soldering looks great from what i can see,flowed through the hole and everything.
Took out the 2399s and I'm still getting signal at c3 and very very low signal at output. When the ICs are out, though, the quality of the sound is different. I don't hear the echo--just clean signal. I don't have anything to swap in for them.
I just got a new soldering station that I'm really pleased with, so I was super confident with my connections. Lol...that's the way it goes, I guess.
for my two cents, I think there is something wrong with Q1/Q2 voltage.
both E legs go to ground and should not have any reading (I think), where Q2 reads 0.06
Q1 - 2.36, .63, 0
Q2 - 2.37, .63, .06
Given the sensitivity of trannies (and the option to experiment), I socket ALL transistors. From your pictures, it appears that Q1/2 and the 78L are directly soldered to the board.
I will defer to the wisdom of the moderator(s), as this is more an observation.
I am building the ZPSDX and am trolling similar builds on the lookout for possible build problems and the experience of others.
Well...Still no joy. I replaced both of the 2399s and get the same problem. I will take a look again at my transistors. I don't remember if i mentioned it somewhere earlier in this thread, but removing the sockets and soldering the transistors direct to the board was one of the first fixes I tried because they didn't feel secure in the sockets.
I'm just looking at the thread for the first time and trying to follow everything you've done so far, so sorry if I ask any redundant questions. Have you checked if there is continuity between the output and ground by using the continuity setting on your meter? What transistors did you use?
If I read what you've said right, you've got at least some signal up to the output cap and then it's dead at that point. The resistor on the output is in the right range, so that shouldn't be the problem. It seems that it either has to be the output cap is bad or you are shorting to ground somewhere after the cap (in the jack or footswitch or at the board). Do you have a voltage reading for the output pad?
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!
Quote from: eshelton on July 29, 2013, 11:04:36 PM
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.
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!! >:(
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.
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.
By the way...Huge thanks to you for your help, Rob! ;D
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?
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 (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.)
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...
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 ;D