EAT tremolo doesn't work

[norcal steve]

Built the Eat Tremolo. Have double checked all the component values and solder joints. Wire connections appear to be correct. Symptoms are:

1.No tremolo effect. Bypass works. With tremolo switch engaged, only a loud hum variable with the volume control. Status and speed LED's work.
2.Name of the circuit = EAT Tremolo
3.Source of the circuit (URL of schematic or project) = http://www.generalguitargadgets.com/projects/26-tremolo/142-ea-tremolo
4.Any modifications to the circuit? N
5.Any parts substitutions? If yes, list them. N
6.Positive ground to negative ground conversion? N
7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 0
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 0
Voltage at the circuit board end of the black battery lead = 0

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
D = 6.33
S = 1.47
G = .94

Q2
D= 0
S= 0
G= 0

Q3
C= variable
B= .57
E= 0

Q4
D= 9.58
S= 5.40
G= 3.14

Thanks for any assistance.

[Mark Hammer]

Those zeros on Q2 are pretty telling.  That would be your problem, I suspect.

[norcal steve]

According to GGG, D and S are supposed to be 0, but G should be variable.

[R.G.]

DC checks look OK within a first pass. That means it's probably a wiring, soldering or component orientation issue, or other less probable issues.

(1) does the hum on the volume control vary with the depth and speed settings at all?
(2) does touching your finger to the junction of R15 and R16 cause more or less hum, or no change at all?

If these don't isolate it, you're probably going to need to follow the signal with an audio probe.

[norcal steve]

Speed and depth control make no audible changes.

Hum is louder when touching R15 + R16.

Have hooked up a capacitor to a shielded cable, but not sure how to trace the signal path past the input jacks.

Thanks

[R.G.]

Speed and depth control make no audible changes.

That means you have two problems. One is that signal is not getting into the amplifier path, the other is that it's not modulating what signal is there.

Hum is louder when touching R15 + R16.

When you touch R15 + R16, you are injecting hum picked up by your body capacitance into the high impedance of the JFET gate at the input. Since this gets to the output, signal is flowing in some fashion through the JFET, through the NPN transistor and to the output. Therefore, your guitar signal is not reaching the junction of R15 and R16. Your problem (at least one of them) is that signal is not getting to the junction or R15, R16, and the gate of the JFET. Hence, it's either in the input jack wiring, signal bypass switching, or R1/C8 connections.

Have hooked up a capacitor to a shielded cable, but not sure how to trace the signal path past the input jacks.

You touch the audio probe/capacitor to, in order:
- input jack signal terminal/tip
- if signal there, touch it to the junction of R1 and C8; test for signal in both alternations of the bypass switch;
- if neither alternation of the bypass switch gives signal, test for resistance of R1/C8 to ground, in case it's shorted. It should measure the same as R1, about 1M.
- if neither alternation give signal at R1/C8 and R1 to ground measures about 1M, signal is not getting to R1. It's a problem in your switch or wiring.
- if one alternation of the switch gives signal at R1/C8, then C8 or the soldering wiring to it is bad.