EA Trem - Boost works, LED flashes, but no trem

[alltherightpills]

Hi Friends,

I'm working on a version of the EA trem from this schematic: http://www.home-wrecker.com/eatremolo.html
Based off of this perf layout: http://effectslayouts.blogspot.com/2014/12/run-of-groove-modified-ea-tremolo.html 

I've got an old GGG layout on perf working perfectly, so I thought I was in for a simple build (famous last words, I know).

The board is built, passes audio and the Volume pot boosts the signal as expected. The rate LED flashes and changes speed with the pot, so I'm pretty sure that the LFO is working.

Modifications / Substitutions:
-subbed 2N7000 for Q1, 2N5457 for Q2.
-Rate pot is a 500k w/500k resistor across outer lugs.
-100k for the 120k coming off of Rate lug 3.
-I am building a dual-speed version, with an extra stomp switch between 2 rate pots, also using a bi-color LED to show the difference. The rate switch is working, LED changes colors and the corresponding pot adjusts the LED flash speed.
-paralleled a 2nd 10k resistor across the LED resistor

I'm fairly sure that my issue is somewhere around Q2 since I can tell Q1 is boosting and Q3 is wiggling. But hey, I could certainly be wrong.

I've been scouring old EA Trem troubleshooting posts, so here's what I've tried:
-checked & rechecked all transistor pinouts
-subbed other transistors (with same part #s, also tried 2N3819 & 2N5458 for Q2)
-checked the wiper of the Rate pot for voltage fluctuation (yep)
-soldered a 10k pot between the 22uf cap & ground to check that it changes volume when turned (yep - this was recommended in an old DIYSB thread)
-checked each resistor for proper value
-cleaned and reheated solder, making sure nothing is shorted


And here are my voltages:

Q1
G: 2.51V
S: 1.31V
D: 4.54V

Q2
G: +3ish to -3ish V (fluctuates with rate, larger fluctuation as depth is increased)
S: 0V
D: 0 to 0.4V (fluctuates)

Q3
C: 0-7V (fluctuates w/ rate)
B: 0.61V
E: 0V

Thanks for reading. Any ideas?

[Rob Strand]

Thanks for reading. Any ideas?

According those measurements it's all working. 

Seriously,

'm fairly sure that my issue is somewhere around Q2 since I can tell Q1 is boosting and Q3 is wiggling. But hey, I could certainly be wrong.

Agreed.

-soldered a 10k pot between the 22uf cap & ground to check that it changes volume when turned (yep - this was recommended in an old DIYSB thread)

OK more evidence it is working and problem is around Q2.

G: +3ish to -3ish V (fluctuates with rate, larger fluctuation as depth is increased)

Good.  So the gate is being driven.
But maybe an issue here as normally the 0.47uF cap charges negatively so the gate voltage is 0.6V max and swings negatively below that.

-subbed other transistors (with same part #s, also tried 2N3819 & 2N5458 for Q2)

That's means there's a systematic problem. 
Maybe a short between Q2's D and S on the PCB?
Maybe open on the source of Q2, or, open between the 22uF and Q2.

Another possibility is the 0.47uF cap on the output of the LF is shorted.
[Edit:   On second thought maybe not since your are seeing some negative swing on the gate.]

When you have the JFET connected is the volume level loud or soft, alternatively, where would it be in comparison to the 10k pot setting?

[alltherightpills]

Maybe open on the source of Q2, or, open between the 22uF and Q2.

Thanks Rob, this was it. One of the pins on Q2's socket was cracked open. Replaced the socket and all is well. Dual Trem complete!

[Rob Strand]

Trem complete!

Cool!

(I'm glad it wasn't one of those dodgy JFET threads.)