Chimaera troubleshooting

[jball85]

I recently built a Chimaera that is misbehaving. I don't have access to an audio probe until tomorrow. Until then, I figured I would see if anyone on this forum would like to take a look at the thread and video of the build, and see if they might be able to shine some light on the troubleshooting.  Here's the link to the Grind Customs Forum thread,

http://www.grindcustomsfx.com/forum/viewtopic.php?f=3&t=616&p=3403#p3403

[mgwhit]

I've never looked at Rej's Chimaera circuit, but if this is a Klon clone, there should definitely be approximately -9V on pin 4 of IC2.  I'll look at that in a minute.  I'm more concerned about the 8.06V on pin 7 of IC1.  You've probably got a solder bridge or a bad joint somewhere near there.

Your IC2 pin 1 and pin 7 voltages are off, too.  Can you remeasure those?  If they were as off as they appear to be I would expect them to mess with the voltages on the other op amp pins a bit.

[jball85]

I measured the IC's again here's the results.

IC1 TL072
1: 4.41
2: 4.41
3: 3.4
4: 0
5: 5.14
6: 4.87
7: 7.47
8: 8.07

IC2 TL072
1: 13.42
2: 4.37
3: 4.39
4: -7.62
5: 4.39
6: 4.39
7: -4.61
8: 14.5

IC3 TC7660SCPA
1: 8.05
2: 4.7
3: 0
4: -3.11
5: -7.59
6: 3.38
7: 4.81
8: 8.04

I tried debugging with a makeshift probe, and I got to R9 (2k) or the (Gain 1) lugs 2 and 3 when I lost the signal. Although I'm not even sure if I'm going about tracing the signal correctly.

[mgwhit]

I think you should try to figure out why your voltages are so whacked out before you do anything else, and the first question I would try to answer is, why is your primary 9V voltage so low (8V)?  This might be a super easy one, and it probably won't fix your problem entirely, but it's a good first step.  Is that what you're getting from the wall, or are you using a weak battery?  (Are you using a test rig?) 

[upthepunxxx]

Dude you are the klon klone trouble shooting expert!!! I love it!

I think you should try to figure out why your voltages are so whacked out before you do anything else, and the first question I would try to answer is, why is your primary 9V voltage so low (8V)?  This might be a super easy one, and it probably won't fix your problem entirely, but it's a good first step.  Is that what you're getting from the wall, or are you using a weak battery?  (Are you using a test rig?)

[jball85]

I'm using a Panasonic battery, it was fresh when I started the build but has lost some juice and now sits at about 8.5-8.6v. I replaced the battery with a fresh one, and I'm getting more 9.2-9.3v where the 8 volt readings were. The low voltage in the 1st battery is just a testament to how much I've been tinkering with this thing.

[mgwhit]

I'm using a Panasonic battery, it was fresh when I started the build but has lost some juice and now sits at about 8.5-8.6v. I replaced the battery with a fresh one, and I'm getting more 9.2-9.3v where the 8 volt readings were. The low voltage in the 1st battery is just a testament to how much I've been tinkering with this thing.

More of a testament how how much current your board is chewing up!

I'm still thinking that you need to tackle the voltage issue...but...as long as you have the audio probe, can you test pins 5, 6 and 7 of IC U1?  Turn down your amp volume first, as this can get loud!  I'm wondering if you're getting the splattiness on that op amp stage or not.

[jball85]

Starting with volume and tone at noon and the gain knob turned clockwise about a 1/4 turn I get a clean signal on pin 5, a very quiet clean signal at pin 6, and a clean signal louder than pin 5 on pin 7. If I turn it all the way off (left) I have a clean signal on pin 5, no signal on pin 6, and a distorted splatty signal on pin 7.

I did have c8 and c7 swapped, there was a silk screen error that I misread. Before I swapped them, the pedal sounded exactly like it does now, even though the components are now in the right place. I did use a new capacitor for the ceramic, but I'm wondering if I somehow ruined it with heat when installing the cap the second time around.

[mgwhit]

Starting with volume and tone at noon and the gain knob turned clockwise about a 1/4 turn I get a clean signal on pin 5, a very quiet clean signal at pin 6, and a clean signal louder than pin 5 on pin 7.

I think that's what we should expect, but don't quote me on that.

If I turn it all the way off (left) I have a clean signal on pin 5, no signal on pin 6, and a distorted splatty signal on pin 7.

Hmmm.  What happens on pin 7 when you turn up the Gain to halfway or 3/4 or full?  Does it get louder or quieter.  Stay clean or distort more?

I did have c8 and c7 swapped, there was a silk screen error that I misread. Before I swapped them, the pedal sounded exactly like it does now, even though the components are now in the right place. I did use a new capacitor for the ceramic, but I'm wondering if I somehow ruined it with heat when installing the cap the second time around.

I don't think those caps should cause any problems even if they're trashed (which is highly unlikely).  I think they're just there for tone shaping.  If C8 were to fail open, things might get weird, though.  Just for giggles, test continuity across the legs of C8.

[jball85]

I'm actually doing some guitar tech work in Dallas but I'll be back on Sunday to get back to debugging. So if u don't mind check back on this thread tomorrow evening, I'll probably have an answer to those questions then.

[jball85]

Update...
1) Ok so I checked continuity on c8, and while my DMM doesn't beep, it does show a forward voltage of 1.015 with no power running through it, but has an infinite reading when the effect is powered and switched on.

2) I probed pin 7 (IC1) and began to increase (clock wise) the gain knob from zero. The signal gets amplified until the halfway point at which the signal just fades out, and passes no signal what so ever.

3) I'm probably getting ahead of myself, but I'm also wondering why I have negative voltage at pin 7 of IC2. I tried replacing c16 with a regular electrolytic ( I had a bipolar Nichicon in there to begin with). That didn't fix the issue.

[mgwhit]

2) I probed pin 7 (IC1) and began to increase (clock wise) the gain knob from zero. The signal gets amplified until the halfway point at which the signal just fades out, and passes no signal what so ever.

I gotta admit this one is a puzzler.  Have you established that pin 2 of your Gain1 pot has continuity to the positive leg of C22?

3) I'm probably getting ahead of myself, but I'm also wondering why I have negative voltage at pin 7 of IC2. I tried replacing c16 with a regular electrolytic ( I had a bipolar Nichicon in there to begin with). That didn't fix the issue.

Yeah, your voltages (and the high voltage on U2:pin1 and the negative voltage on U2:pin7 in particular) are really the $20,000 Question.  There are only a couple of points in the circuit where negative voltage is even available!  I know you mentioned in your other thread that you've swapped in new TL072s, but could you swap a different TL072 in U2 and compare the voltages between the two chips.  If both chips produce the high voltage on on pin 1 and the negative voltage on pin 7, then I think you should take a resistance reading between pins 1 and 8 and pins 7 and 4 on the socket with the circuit powered down and the chip out.

I've never built any of the Klone circuits, so I don't really know exactly how this should behave.  I can't compare it to anything I've got.  (I've got a Kingslayer sitting on my desk that I'm going to populate this week, but that's a slightly different beast.)  I'm just looking at the schematic and trying to apply what little I know about electronics.  The IC voltages that other people have posted for these circuits are exactly what you would expect given the off-kilter split-rail power supply.  Given that yours are so far off, the best guesses I have are (a.) solder bridge (possibly under the socket!), (b.) bad joint,  or (c.) bad component (unlikely).  Keep trying!

[jball85]

I swapped in a different chip and got the same readings pretty much. I measured for resistance between pin 1 and 8, as well as 7 and 4. I received an infinite reading for both sets of pins. The meter measures up to 2m ohms. My other meter which measures up to 200m, all of the sudden magically broke down and now reads 666 on every setting. Now, I'm officially pissed.  I can't find any bridges anywhere on this thing, and none of the electro's (that I can't see under) have continuity.

[jball85]

I popped two other Tl072CN's in the IC2 spot and got negative voltage readings at pin 1 and 14 volts at pin 7. This is leading me to believe that these TL072CN's that I bought from Tayda are bunk. However, I do remember building a G2D Cream Tone which used 3 of them and it worked flawlessly, and sounded almost exactly like a genuine Cream Tone. Maybe they just don't work with this circuit. Idk, this is beyond me.

[jball85]

I got some different TL072's, no difference. I changed the charge pump, no difference. I changed the gain pot... No difference.