Tri-Vibe problem

[theehman]

I have a ROG Tri-Vibe here that I got somewhere.  I wasn't too thrilled with the chassis layout so I redid a few things and cleaned up the wiring so it looked a bit better.  It was working great but then I was working on adding the LFO LED when it quit working.  I can still hear a change in tone with the switch but there's no modulation.  An audio probe on the TL064 didn't find any ticking so I replaced the TL064 to no avail.  Maybe I just need a fresh set of eyes here.  To be honest, since my cancer surgery in 2019 I feel like I'm not as sharp as I used to be.

My supply voltage is 9v

TL072 pins
1) 4.54
2) 4.53
3) 4.12
4) 0
5) 4.53
6) 4.53
7) 4.53
9.08

TL064
1) 4.53
2) 4.53
3) 4.51
4) 9.08
5) 5.12
6) 5.07
7) 8.23
8.29
9) 0
10) 4.53
11) 0
12) 8.25
13) 4.49
14) 8.3

LM13600
1) 1.32
2) 5.4
3) 4.75
4) 4.75
5) 5.65
6) 0
7) 5.65
4.43
9) 5.0
10) 6.23
11) 9.0
12) 6.23
13) 4.75
14) 4.76
15) 5.4
16) 1.3

Anything stand out?

[r080]

I am a little confused trying to map the 4 opamp package to the runoff groove documentation, but if I have this right, it seems like your TLO64 pin 9 should be at VRef. It seems like that is the area you would have been working on adding the LFO LED. Perhaps there is now a bridge to ground at pin 9?

[ElectricDruid]

+1 agree.

The TL072 looks fine, but the 064 is suspicious in various ways. Without knowing exactly what's doing what on that chip, it's hard to say specifically, but it's not right.

[r080]

If you can post any documentation you have on your board (or a picture), it would make it easier to confirm which opamp is supposed to be doing what. Also, are any of your voltages varying? Based on your description of the problem, it seems the LFO is not running.

Again, I could be confused about what is what. I could also have basic opamp theory a bit off. I think pins 8, 9, and 10 match the runoff groove documentation U3B out, -in, and +in, respectively. You are getting ~8V, 0V, ~4.5V on those pins. The +in should be connected to vref, and the opamp should be keeping the -in around vref as well. Your pin 10 should be where you were trying to get your LFO indicator. If pin 9 was grounded, I think your opamp will be an inverting comparator, and you will always get a high output, which is consistent with your voltages.

http://runoffgroove.com/tri-vibe.html


My posting here is half selfish. I have a tri-vibe queued up as my next build, and I want to learn what can go wrong on it.

[theehman]

Thanks for the input, guys.  I tracked pin 9 back and it looked like it was shorting to the case through the Speed pot lug.  It's working great now and I finished installing the LFO LED.