Does anyone have voltages from a working Stage Fright?

[midwayfair]

Not having a good run here ...

My multimeter battery died so I don't have voltages on the LM13700s.

IC1 voltages look "normal" but there's no signal on pins 6-8.

LFO is working -- the LED flashes and I can get woosh woosh noises. But I had to sub a BJT chip to get it to modulate at all. Neither TL072 or 062 would work.

My only subs are 27K and 33K for the 30K resistors. I'm not sure it can make much of a difference since I think to the electrons it's same thing, right? They're two resistors in series.

Okay, audio probe. Dry signal passes at about unity. But this is super weird: I can get weak signal at pin 7 of IC3 (before the buffer) but nothing anywhere else on any of the 13700s or anything attached to them. It is weakly modulated. However, if I pull IC3 and jumper pins 4 and 8, I can get stronger signal at IC5, with some very chewy phase ... but no signal on ANY other pin of the 13700s, not even after the next inversion! I tried jumpering the other half of IC3 on the assumption that there was something wrong in that side of the board, and then I can't get anything but LFO noise on any pins on the 13700s. I tried bypassing all the stages at one point or another (though I did not pull any resistors, just jumpered 13700 pins).

A few other things: I got better dry signal with a 274 in place of the 074, but nothing else changed. I've tried about 10 different 13700s from three different suppliers, and a couple 13600s from Smallbear. All tested as working in an engineer's thumb.

One last thing: this is the board that I desoldered all the chips from. There was one lifted pad in the LFO chip. I double checked everything with my multimeter for continuity and the only bad spot I found was that somehow the base of Q1 was not connected to the R49/R50 junction for some reason (no damage to the board there, though). I'm unable to locate any other PCB damage and as noted above I've tried bypassing various stages.

Pretty mystified right now. 

[RobA]

I don't have them on hand, but I've got a working Stage Fright so I'll measure them now and put them up.

It's in the box and taped down, so a couple of these, especially the 2N5457, are hard to get to. but, I think they are pretty accurate. The other thing to note is that my meter sucks at getting the full sweep of moving voltages. I set the speed to slow, so these moving values should be close to the actual range. The OTA's are all JRC versions of the 13700 (NJM13700D). I used a TL062 and a TL074. The only mod I can recall is that I did the cap sub for the more vibe like feel.

Voltage in: 9.4V

IC1: (TL074)
1   4.67
2   4.67
3   4.25
4   9.33
5   4.64
6   4.65
7   4.65
8   4.67
9   4.64
10   4.55
11   0
12   4.62
13   4.65
14   4.64

IC2: (TL062)
1   0.69 to 8.7
2   4.65
3   2.8 to 6.5
4   0
5   4.69
6   4.68
7   3 to 6 range
8   9.35

IC3: (NJM13700D)
1   1.16 to 1.27
2   0.291
3   4.57
4   4.57
5   5.72
6   0.31
7   5.6 to 5.78
8   4.58
9   4.59
10   5.64 to 5.7
11   9.16
12   5.63 to 5.73
13   4.58
14   4.58
15   0.38
16   1.13 to 1.27

IC4:
1   1.12 to 1.3
2   0.286
3   4.61
4   4.61
5   5.72
6   0.3
7   5.61 to 5.78
8   4.58
9   4.56
10   5.66
11   9.15
12   5.58 to 5.69
13   4.58
14   4.58
15   0.317
16   1.14 to 1.28

IC5:
1   1.11 to 1.3
2   0.29
3   4.63
4   4.61
5   5.64
6   0.4
7   5.68 to 5.75
8   4.58
9   4.60
10   5.75
11   9.23
12   5.60 to 5.76
13   4.62
14   4.61
15   0.363
16   1.14 to 1.28

Q1:  (2N3904)
E   3.90 to 3.98
B   4.56
C   9.14

Q2: (2N5457)
G   0
S   1.184
D   3.90 to 3.98

Q3: (2N3906)
E    4.56
B   3.90 to 3.98
C   1.13 to 1.38

[midwayfair]

Rob, thanks so much.

Yeah, several of my LM13700 pins are very wrong, and more of them are moving than on yours. Also found that I have 7V on pin 8 of the 074.

I might just rebuild this. It's possible that I did damage the board in some way, and tracking down a couple wrong voltages isn't too bad, but tracking down a dozen is just a pain.

Off to work now, so I guess I'll fiddle more when I get home if I haven't taken advantage of the sale.

[RobA]

Sure thing on getting the measurements.

As far as you seeing more moving voltages on the OTA's, I see that in my measurements pin 5 isn't moving. That doesn't really make any sense. It should be the same as pin 7. My guess is that I just didn't leave the probe on long enough to see the movement on the first IC I measured and when the others hit the same value, my brain was set to too quickly accept it. (Confirmation bias of a sort). I could also see that there might be some small movement on pin 4 and 13 and maybe even 3 and 14 from the feedback paths.  They seemed pretty steady to me when I measured them, but it could be that my meter just didn't pick it up well or you would see it more with a different setting of the trimmer and/or speed. If the movements you are seeing on those pins are small and around the values I saw, they may be fine.

[midwayfair]

Sure thing on getting the measurements.

As far as you seeing more moving voltages on the OTA's, I see that in my measurements that pin 5 isn't moving. That doesn't really make any sense. It should be the same as pin 7. My guess is that I just didn't leave the probe on long enough to see the movement on the first IC I measured and when the others hit the same value, my brain was set to too quickly accept it. (Confirmation bias of a sort). I could also see that there might be some small movement on pin 4 and 13 and maybe even 3 and 14 from the feedback paths.  They seemed pretty steady to me when I measured them, but it could be that my meter just didn't pick it up well or you would see it more with a different setting of the trimmer and/or speed. If the movements you are seeing on those pins are small and around the values I saw, they may be fine.

Ah. Most of the movement was small. But e.g. pin 7 on IC3 for me is super low (like 1V), and several other voltages were off.

I can't really explain the 7v on my TL074's pin 8, either. I can't think of what could pull it up that high; even if there was a solder joint under the chip that I can't see, nothing near that pin has voltage higher than Vb.

[RobA]

...
I can't really explain the 7v on my TL074's pin 8, either. I can't think of what could pull it up that high; even if there was a solder joint under the chip that I can't see, nothing near that pin has voltage higher than Vb.

Yeah, I agree that it is weird. I can't see where it might be coming from either. Maybe something is wrong in the IC itself? But, you've tried a 274 in there too. Puzzling for sure.

[midwayfair]

Ahh, screw it, the board's on sale with free shipping ....

[RobA]

Ahh, screw it, the board's on sale with free shipping ....

Could save a lot of headache if the board you have is messed up. And that reminds me that I need to take advantage of the sale too.

[GermanCdn]

Ahh, screw it, the board's on sale with free shipping ....

I had a few funky parts too and went this route, a whole lot less headaches, and fired up right the first time.