GGG Phase 100 don't phase

[jimilee]

So this was started on another thread and it's time to move it to the tech help section. I really some magic smoke ad now the phase 100 doesn't phase. Here's what I know thanks to Jon probably the IC's,so here are my voltages. There are 6 of them and they are all TL072.
IC-1 (Im guessing this one has the issue)
4.5
4.5
0
0
9.1
.6~8.4 fluctuates
5.3
3-5.5 fluctuates

IC-2
4.5
4.5
4.3
00
9.1
4.5
4.5
4.0

IC-3
4.5
4.5
4.0
0
9.1
4.5
4.5
4.3

IC-4
4.5
4,5
2,1
0
9
4.5
4.5
4.0

IC-5
4.5
4.5
3.9
0
9
4.5
4.5
4.2

IC-6
4.5
4.5
4.3
0
9
4.5
4.5
4.3

I'm thinking it's IC-1 because the voltages are fluctuating and that doesn't look to be normal. (Like how I figured that one out? I'm a sharp one.)

[jimilee]

Magic smoke bump

[the3secondrule]

Coupla things:

1) Can you put up a link to the schem?

2) without the schem I'm only guessing here, but the fluctuating voltages on IC1 would suggest to me that ic1 is the lfo?

Maybe some pics? And if its smoked, check for solder bridges and anything that might've cooked 

Jeremy

[jimilee]

Coupla things:

1) Can you put up a link to the schem?

2) without the schem I'm only guessing here, but the fluctuating voltages on IC1 would suggest to me that ic1 is the lfo?

Maybe some pics? And if its smoked, check for solder bridges and anything that might've cooked  

Jeremy

Will do, it worked before it smoked. I was wiring up the selector knob. http://generalguitargadgets.com/pdf/ggg_p100_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

[midwayfair]

For reference, here's the schematic:
http://generalguitargadgets.com/pdf/ggg_p100_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Jimi, post some pics when you get a chance.

Also, I'm not sure how you've measured the voltages on the op amps, but you should post them in the pin number order:
1     8
2     7
3     6
4     5

In any case, it looks like IC1A pin 3 is grounded or not connected to anything. This is a bad sign: it should be tied to Vb via a 100K resistor, and it should be close to the voltage of the component it's directly connected to, IC2 pin 7, and, being constructed identically, it should also be close or identical to the other pins in the phasing stages (all the + inputs of those op amps in the center of the schematic). You've either got a short, a broken trace, or the chip is bad. I'd actually replace the chip first if you used a socket (then test it in another working build that uses a dual op amp before tossing it if you like) to avoid the frustration of troubleshooting around a blown component.

[jimilee]

Ohhhh I did 1-8 sorry about that. I'll start with that op amp and socket it. I bought it from a guy over on byoc. It was working then I shorted it out. Definitely my error.

[jimilee]

So I replaces IC 1 and bow have voltage on pin 3 but still no phasing. What should I check next? I didn't pull the vactrol.

[jimilee]

Bump before it's #1 in a box of fail bump

[midwayfair]

Bump before it's #1 in a box of fail bump

Sorry, Jimi. I could recognize what was wrong in the op amps, but my experience with this circuit is basically nil.

Did you check if the LED in the vactrol isn't blown (measure for continuity across it ... you don't want continuity.)

[electricstorm]

Have you checked the vactrols yet? You can do this in one of two ways. Remove them from the circuit and check from the center lead to each end lead (the side with 3 leads), if you get resistance, it is good. Or, use your volt meter and check them in circuit while powered up. You should have fluctuating resistance on each vactrol. Be very careful doing this as you don't want to short out anything
. Also, set the rate to a slow sweep so the meter has time to rect.

Also, since IC1 was part of the LFO, check the transistors in the LFO circuit. Or, better yet, temporarily add an LED is parallel with the LED side of the vactrol and you could tell right away if the LFO is working (just make sure to have it connected with correct polarity). Once verified, remove the temporary LED.

You said you replaced IC1 and got voltage on pin 3, what are the voltages for the IC's now? Did any voltages change for any IC?

Jim

[electricstorm]

Jimilee,

Did you get this going?

Jim

[jimilee]

Nope. I still need to check the transistors next though. Sometimes you gotta let it be and think on it.

[jimilee]

Jimilee,

Did you get this going?

Jim

Ok , so I have resistance that fluctuates on each of the vactrols,BUT an led in parallel doesn't light up,so I would assume that the transistors are non functioning? Also I measured for continuity across the LED side of the vactrols. The first vactrol on the lower left has continuity but the other 2 do not.

[electricstorm]

OK, if two vactrols don't show continuity, you shouldn't have any fluctuation of resistance (unless I'm reading the schemo wrong). Use you voltmeter and check the voltage on the collector of Q1 and Q2 (they form a darlington transistor). Set the rate of the LFO to a slow to medium setting so the meter has time to react. If you have fluctuating voltage, the LFO is working. I don't recall seeing a depth control, so the speed should be all you need to adjust to check this.

If the right most two vactrols don't have continuity, place an LED on each of them as before (one on each that didn't read continuity) and they should light up as the LFO sweeps. Or you could place a single LED from 9vdc through a 470 ohm resistor and connect the other end to the collector of Q1/Q2 to verify the LFO works (this is if you don't want to use the volt meter). If this is the case, the LEDs in the vactrols are bad for sure.

[jimilee]

I touched an led to each vactrol the and nothing lit up. The right most vactrols gave me fluctuations through the volt meter. I will test the trannies with a volt meter next.done,the collectors fluctuate.