Wacked out KLON. Debugging please.

[italianguy63]

Been working on this one awhile.  At wits end with it.

I have double and triple checked component values, for solder bridges, and wiring.

It makes a weird warbling sound when engaged.  Some voltages are way off.  Almost certainly a bad (something?)

Voltages:

IC1- TL072
1 - 4.13
2 - 4.13
3 - 3.21
4 - .3
5 - 2.79
6 - 3.72
7 - 1.30
8 - 9.31

IC2 - TL072
1 - 16.08  (ouch)
2 - 3.34
3 - 4.12
4 - -8.98
5 - 4.14
6 - 4.36
7 - -7.21 (another ouch)
8 - 17.11

IC3 - ICL7660S
1 - 9.37
2 - 4.67
3 - .2
4 - -4.45
5 - -8.94
6 - 4.78
7 - 7.20
8 - 9.35

I have replaced IC2 with no change.  I also have "normal" voltages if anyone needs them posted.

Any ideas?

MC

[Kipper4]

Bean posts some voltages here.

https://www.diystompboxes.com/smfforum/index.php?topic=116779.msg1082638#msg1082638

[italianguy63]

Thank you.. I have what the voltages should be. 

I'm just stumped on this one... I read through another thread with similar issues, and it didn't help either.

I know the "Captain K" gets no love here.. but, I have used up my other resources/knowledge.  Not posting pics or schematic...

Today, I just started refloating the solder connections, as I just don't see anything wrong.

I used to socket the IC's, but I didn't on this one.  Wish I had...

MC

[thermionix]

You've got fractions of a volt where you should have dead zero.  Maybe a bad ground run with some resistance?

Also...commercial PCB or homemade?  Could be an error.

[reddesert]

It helps if you can at least post a link to the schematic.

Pins 1 and 7 of IC2 have wrong voltages, pegged to the rails. These are op-amp outputs and the input voltages are okay. That suggests maybe something is wrong with the feedback networks around those op-amps.

Pins 5,6,7 of IC1 are a little weird but those might change with the Gain pot setting (look at how Vbias is connected to the opamp through the gain pot to see why).

[italianguy63]

You've got fractions of a volt where you should have dead zero.  Maybe a bad ground run with some resistance?

Also...commercial PCB or homemade?  Could be an error.

PCB for sure is OK.  Homebuilt.. but, not the first I have built.

[italianguy63]

It helps if you can at least post a link to the schematic.

Pins 1 and 7 of IC2 have wrong voltages, pegged to the rails. These are op-amp outputs and the input voltages are okay. That suggests maybe something is wrong with the feedback networks around those op-amps.

Pins 5,6,7 of IC1 are a little weird but those might change with the Gain pot setting (look at how Vbias is connected to the opamp through the gain pot to see why).

Schematic is by Martin Chittum, April 15th, 2009.  I think it is pretty common in the public domain by this point.  This particular schematic is considered the "correction" to some earlier ones.  I won't post it to keep Aron happy(er).

Thanks for your help-- I will not be around most of the day tomorrow, but it you can suggest any areas to review I will.  But, I know the component values are right.  I looked at them yet again this morning.  IC2, the GAIN (twin) pot, and C16 are all verified good (replaced).  Just scratching my head.  I'm betting a bad electro cap maybe?

MC

[reddesert]

I know how to find a Klon schematic, but when discussing debugging one has to know one is working off the same schematic with the same part numbers.

I don't have any way of guessing which part might be a problem. (IME solder joints and bridges are faulty more often than parts.) I'd suggest measuring voltages (not just on the op-amp pins, but at the passive components as well) and audio probing through the circuit in the identified problem area around IC2(A) to find where things are going wrong. Keeping in mind that you should not hear any signal when audio probing the input of an inverting op-amp stage, so that's not necessarily a problem.

[pinkjimiphoton]

when i had this same problem, it was due to a diode in backwards

waaaaaaay back when baja's sag charger was all the rage. the first runs of board had one of the diodes marked on it backwards, cuz someone thought the band was the anode, not the cathode.

i was pulling my hair out til i found the bug... same thing, backward voltages from what i expected to see... perhaps you did the same?

[italianguy63]

when i had this same problem, it was due to a diode in backwards

waaaaaaay back when baja's sag charger was all the rage. the first runs of board had one of the diodes marked on it backwards, cuz someone thought the band was the anode, not the cathode.

i was pulling my hair out til i found the bug... same thing, backward voltages from what i expected to see... perhaps you did the same?

Thanks Jimi-- checked it again.  Diodes are all right.

Just checked all the cap orientations too.. all correct.

and checked switch wiring again.

This one is a head scratcher.

MC

[Big mike 1100]

Just a random thought-Is the issue the same regardless of where the volume and gain knobs are set?  With my build, when the gain is set anywhere past 3:00 I get the "warble" sound regardless of how low the volume knob is set.  I think it might be something with the dual gain pot, but haven't investigated it yet.

[italianguy63]

I replaced the dual gain pot.  No, it just seems to warble all the time.  I replaced the pot as the pot values did not measure right while on the PCB.  When unsoldered, it was OK.  So maybe something around there, but I just don't see anything.  Many hours spent on it.

I am starting down the path of just building a new PCB and putting this one into the death bin.

MC