Echo Base: No power, no sound, no LED.

[Slidester]

I just finished building the Echo Base. I have no power, no sound and no LED. This is not my first build; I'm careful and have good soldering skills. I check capacitor and resistor values before I solder them in. I noticed that some builders socket their transistors, which I have never thought to do. I'm wondering if I might have overheated a transistor by soldering it in. I have given this a thorough visual inspection and did some checking for continuity and ground. Everything looks good. i installed the tails switch and LFO switch and did the basic resistor substitution from 47K to 22K. Is there one IC or transistor that, if faulty, will cause the problem I'm having? Any ideas will be appreciated. If I can't get this one working I think I'll just order another board and try again. Thanks in advance.

[jez79]

Give us a link to the schematic you used

[slacker]

The problem won't be anything to do with not socketing the transistors, even if you completely destroyed the transistors that would just stop the bypass or modulation from working. If you killed the TL072s or the CD4066, by putting them in backwards or something that could short out the power and stop the effect working, something would probably be getting hot if you'd done that though.
I assume you're using the musicpcb PCB, when you say you get no power do you get any voltage at all if you measure the voltage across the 9V and G pads on the top left of the board? If you get nothing, check that those two pads aren't shorted together by a blob of solder or something.Next thing I would do is check the 1N4001 diode bottom right on the board is the correct way round, the bar on the diode should be towards the edge of the board, if that's backwards the pedal won't work. If that's the right way round and you used sockets try removing all the ICs and then measure the voltage across the 9V and G pads if you then get about 9 Volts try putting the ICs bck in one at a time and measuring the voltage each time, this might help show where the problem is.

[Slidester]

Thanks for the reply. (I'm using the musicpcb Echo Base PCB. Sorry for not mentioning that. I did not know there are others available.)

I checked voltage at the 9V and G pads, then went through the recommended steps. I always measure 9V: ICs out and back in one at a time. It always measures the same.

One change: I was not seeing ground at the output jack so I star grounded it to the power jack. The pedal now passes weird sounding audio - hard to describe, kind of a high-pitched motorboating. Definitely not a desirable delay sound. LED still does not light.

[bluebunny]

Go and follow the instructions in the sticky "Debugging" thread.  It really works.  Some pictures of your board and wiring may help too.

[Slidester]

I have made a visual inspection of all capacitors (all are labeled as correct values and oriented correctly) and checked values on all resistors. 3 resistors read significantly different than spec. I tried changing one, but it read OK once out of the PCB. That one is a 220K than seems to be connected to the Tails switch. It reads 18K when soldered in. The 680K that looks to be connected to pin one of TL072 U1 reads about 500K. The 1.5M connected to pin 5 of U1 reads 680K. I did not try changing these two.
I checked the pins on all the ICs. The pins that are not correct according to supplied values:
PT2399 pins 7 and 8 read .84V.
TL072 U3 reads 9.8V on pin 5.
The 4066 (CD4066BCN) has the following values:
1. 4.6v
2. 4.6v
3. 0
4. 0
5. 0.51v off
7. 0
8. 4.8v
9. 0.95 on or 0.07v off
10. 4.6v
11. 4.6v
12. 9.6v
13. 9.6v
14. 9.8v
I tried disconnecting the bypass, tails, and LFO switches to see if that made any difference. No change. I also tried a different LED.
I have not tried making and using an audio probe yet, but will do so if that might help locate the problem.
The pedal passes audio, but it is mainly just noise. Whether it is bypassed or not seems to make no difference.

[bluebunny]

3 resistors read significantly different than spec. I tried changing one, but it read OK once out of the PCB.

You can't take resistor readings when they're in-circuit, since they're connected to loads of other things.  An audio probe might be a good idea at this point, and a schematic.

[duck_arse]

if U3 has 9V on pin 5, what is the pin 7 voltage? can you pull that IC out of its socket, and measure (and post) ALL the voltages on that socket?

[Slidester]

I had read before about not being able to read resistors once they are on the PCB. I guess desperate measures and all that. Thanks for the reminder.
By way of trying to debug, I touched up all the solder points and then cleaned again with alcohol.
The reading on U3 with the TL072 out:
1. 0        8. 5
2. 0        7. 0
3. 4.5     6. 0
4. 0        5. 9.8

I swapped in one new TL072. All the readings on U3 with the IC installed are now correct.
Overall, still no improvement in sound. No difference if bypassed or not. No LED.
I just finished making an audio probe and am ready with a schematic for my next effort. I can read a schematic but have never used one to find my way around a PCB. (I've watched someone else do it.) Any advice?

[bluebunny]

Any advice?

Start at the input of your circuit and see if you can still hear a noise from your guitar.  Proceed to the next component (use the schematic to guide you) and see if you still get signal out the other side of that component.  When you lose your signal, come back here and tell us!   

[slacker]

Have you got the pin numbers correct for your TL072 measurements?  The numbering goes 1234 down the left hand side and 5678 up the right hand side, so pin 5 is opposite pin 4 and pin 8 is opposite pin 1. It looks like you've gone 5678 down the right hand side so pins 5 and 8 are reversed.

[Slidester]

I typed my TL072 numbers to look like the layout of the IC; down on the left side and up on the right. I'll check again.

[vigilante397]

I hate to be that guy, but how is your switch wiring? I've had plenty of builds that completely checked out with voltages and audio probes, just to find out I made a careless mistake wiring the switch at 2 AM.

[Slidester]

I apologize for any incorrect terminology and unclear descriptions. One could write several books about what I don't understand about all this. I have built several pedals. They have all worked so I have never had to learn this kind of diagnosing. I'm looking at this as a chance to learn a new skill.
I welcome any and all productive suggestions. As for switch wiring, I'm using the most basic switches I know of - on/off, 2 lugs latching for LFO and Bypass and On/On toggle for tails. I tried disconnecting all switches at one point to see if it made a difference.
After using the audio probe today here is what I have found:
I don't hear any audio in what I perceive as the LFO side of the 2399; between pins 1-8 and the 10k-50k resistor.
Between audio In/Out and pins 9-16 of the 2399 i hear audio. (Not necessarily any kind of effect.)
I did find that if I inserted the positive leg of an LED into the socket (I socketed the 50K resistor) of the 50K away from pins 8/9 of the 4066 and placed the other leg at ground I could get a red LED to light. I could not get a bright blue LED to light. Plus there was no pulsing of the LED no matter what setting I tried on the pedal.
I have tried substituting all the ICs. Today I removed, socketed, and replaced the BC560 and the 2N5089.

[Taylor]

I like to "divide and conquer" with debugging. Can you check with your audio probe pins 1 and 7 of the TL072 on the left side of the board, while playing your guitar into it? These are the audio opamp stage outputs. There should be clean guitar at pin 1, and clean guitar plus delayed guitar at pin 7.

Then try pin 10 of the 4066. You should have some delay going on there, but even just hearing some noise which changes when you turn the delay time knob would be a good start, and help focus on the problem area.

[Slidester]

My pedal is now working. Thanks to everyone who helped me on this. I wish I could say exactly what fixed the main issue, but my approach was scattershot; very unscientific. When I was using the audio probe, and subsequently replacing the transistors, I did not check the pedal with instrument and amp each time I made a change. I suspected the audio probe was showing a problem around one or the other of the transistors. I changed them to be on the safe side. After that I mistakenly relied on the LED to tell me if the pedal was working. Today I soldered in a new LED so I could run the checks that Taylor suggested. While I was at it I decided to change the 50K resistor to a 10K. (I had tried this other times with no luck.) When I powered it up it worked.
Thanks again. I learned a lot on this one.