Electro Harmonix Metal Muff weak signal

[almavague]

I was about to order a new transistor, but I thought I'd follow your suggestion before placing an order.

So I got the JFET off the board, but now there's no signal at all, just a bit of hum on the distortion side, and nothing on the bypass side. Should it be working with the distortion turned on? Is this a clue that would suggest other problems?

The voltages are as follows (on the leads with the JFET removed)
8.5v (is this the drain?)
2.15v (lead connected to R56 - is this the gate?)
0v (lead connected to R57 - is this the source?)

[Helmholtz]

So I got the JFET off the board, but now there's no signal at all, just a bit of hum on the distortion side, and nothing on the bypass side. Should it be working with the distortion turned on? Is this a clue that would suggest other problems?

The voltages are as follows (on the leads with the JFET removed)
8.5v (is this the drain?)
2.15v (lead connected to R56 - is this the gate?)
0v (lead connected to R57 - is this the source?)

Now that's disappointing. I was hoping that the distortion would come alive with the shorted Fet removed. Without the Fet no bypass signal.
You correctly identified the Fet terminals (also see the Fet datasheet).

There should be no hum when powered from a battery.

Now verify all voltages given in the schematic and also measure opamp output voltages.

Do you have a scope?

[almavague]

When I did a second test, there is no hum with a power supply, nor the battery. I must have done something funny during the first test.

I think I've done what you asked me to do. As for the opamp voltages (these are the U numbers on the schematic, right?) I believe I already gave them in the first post. I've double checked them, and no change. As for the other voltages, here's what I have:
R2 4.3V
R6 4.3V
C6 4.3V
R8 4.3V
R9 4.3V
R15 4.3V
R19 4.3V
R22 4.3V
LED 1 8.5v
R26 4.3V
R32 4.3V
R35 4.3V
R39 8.5V
R43 8.5V
LED2 8.5V
R52 8.75V one side, 8.5V other side
R53 8.5V one side, 4.3v other side
R56 4.3V

Is this what you asked for? Or do you need the voltages on both sides of the components? Please let me know if this was not what you asked for...
And I don't have a scope.

[Helmholtz]

At first glance opamp voltages look good. I always look if the voltage at the ouput pin is the same as at the inputs (typically 50% of supply voltage, here around 4.3V).

But transistors, where the base is not at least 0.5V (to 0.8V) more positive than the emitter look suspect.

Is your meter battery good?

[almavague]

My multimeter battery is good. I retook the voltages on the transistors, everything is basically as I had mentioned earlier. I took the voltages with the negative terminal of C40 (per your advice) rather than the ground spring, but little difference. It appears that Q1, Q2, Q4, and Q6 all have less than 0.5V difference between the base and the emitter. Thoughts?

Q1 (no change)
B 4.1v
C 8.5v
E 3.7v

Q2
B 4.1v
C 8.5v
E 3.7v

Q3 (no change) Do I have the base and emitter reversed?
B 2.9v
C 8.5v
E 3.6v

Q4
B 4.8v
C 8.5v
E 4.7v

Q5 (no change)
B 0.6v
C 4.8v
E 0v

Q6 (no change)
B 4.3v
C 8.5v
E 4v

Q7 is removed but the leads are:
drain 8.5v
gate 2.15v
source 0v

[Helmholtz]

I still have doubts. Generally collector-emitter voltages look ok. Please measure base-emitter voltages directly: black meter lead at emitter, red one at base.
I think your meter is loading down base voltages otherwise.

[almavague]

Q1 0.59V
Q2 0.59V
Q3 0.59V
Q4 0.64V
Q5 0.59V
Q6 0.63V

Q3 doesn't make sense to me. Base-ground is 2.9V, emitter-ground is 3.6V, but somehow base-emitter (red probe on base, black on emitter) is still + 0.59V. Shouldn't it be a negative voltage?

[Helmholtz]

Q1 0.59V
Q2 0.59V
Q3 0.59V
Q4 0.64V
Q5 0.59V
Q6 0.63V

Ok, all transistors working fine.

Q3 doesn't make sense to me. Base-ground is 2.9V, emitter-ground is 3.6V, but somehow base-emitter (red probe on base, black on emitter) is still + 0.59V. Shouldn't it be a negative voltage?

As suspected, your meter's input resistance is loading down base-to-ground voltages, because base circuits are high impedance.
Meters differ in input resistance. Yours seems to be rather low.

Base-emitter voltages should always be measured directly

[almavague]

If everything looks ok, should I go ahead and order the replacement for Q7 and hope for the best?

[Helmholtz]

If everything looks ok, should I go ahead and order the replacement for Q7 and hope for the best?

A new Fet should restore the dry signal but I don't expect it to have an effect on distortion.

As the DC voltages in the distortion path give no clue, you will need to trace the distortion signal using a scope.
But before I would verify that there are no bad solder joints or connector contacts and that switches and jack switching contacts act as they should.

[almavague]

Hello Helmholtz - It's been a long time - but I ordered the JFet (it took 6 months to come...) I managed to solder it to the PCB, AND THE PEDAL WORKS!!!!!!! A thousand thanks to you, my friend! I have very little experience in electronics and was not optimistic about my soldering, but it worked out!!