Randall RG-120 No Tremolo (& More) Help

[misterc57]

Yes it is hard to read. I meant C35 .047 was replaced.

Most components I pull have very short legs and are difficult (for some reason) to de-solder and I end up replacing them.

The signal is strong (volume wise) and can get very loud at the output of the amp. The only signal is the one I injected at the tank output. Noting is connected to the input of the amp.

So it seems like the recovery circuit is fine?

With a signal injected at the amp input only, should I be detecting a signal at the tank output? I had only detected a signal at the tank input.

Thank you

[Helmholtz]

So it seems like the recovery circuit is fine?

With a signal injected at the amp input only, should I be detecting a signal at the tank output? I had only detected a signal at the tank input.

Yes and yes.

But tank output signal will be very small, only a few mVs.

You should be able to see it multiplied by 15 at Q19 source.

[misterc57]

I have 134 mV at tank input and 8 mV at tank output. There is no gain of that 8 mV signal taking place in the recovery circuit

Also there is no audible signal using my signal listener at the tank output.

[Helmholtz]

Do those 8mV actually look like your signal or is it just random noise?
Where do you connect the ground clip of your probe?

See if the 8mV reach Q18 gate.

[misterc57]

Do those 8mV actually look like your signal or is it just random noise?
Where do you connect the ground clip of your probe?

See if the 8mV reach Q18 gate.

I think it looks like noise. Pics below. First shows pan input, second shows pan output.

Ground clip is connect to a bolt at amp chassis, near recovery circuit.

The 8mV is present through the entire recovery circuit.

[Helmholtz]

So essentially no reverb output.
Pan drive signal is extremely low.

What was your amp input signal, only 10mV?

If so, increase to 100mV. Channel volume and tone controls at 5 (MV down) and repeat.

[Enzo]

Maybe I missed something, the schematic looks like it wants 10 volts into the reverb drive transducer. Not 10mv. My basic test for reverb recovery is to pull the cable out of the OUTPUT jack on the pan, and touch the tip of the plug with my finger. With the amp running and reverb control up midway, I should hear loud hum from that.

[misterc57]

Input signal upped to 100mV. Controls all at midway. See 3.5V at pan input (see pic), no change to pan output (still nothing there).

Next test, removed the pan output plug and touched the tip, I can hear the buzzing through the amp.

[Helmholtz]

Looks like more than one issue.

First test the pan output/recovery cable. Measure DCR of inner and outer conductor from end to end and between conductors.
You should see below 1R between output transducer hot end and input of C32.
As well as below 1R between grounded side of output transducer and amp chassis.

Your drive signal is heavily clipped and only 3.56Vpp corresponding to 1.26Vrms (assuming a sine signal)..
Schematic indicates 10Vrms instead.

Check drive amp DC voltages.

[misterc57]

Under 1R on both + and - side of tank to board.

I could be wrong but I think the clipping is normal and expected on this model which is known for its tube like saturation sound.

TIS58 Q22
D 2.4V
G .9V signal 88mV
S 11.5V signal 1.2V

TIS98 Q23
E 24V signal 6mV
B 11V signal 1.2V
C 10.8V

Bad Q23?

[Helmholtz]

D/S as well as E/C reversed?

[misterc57]

I do not think they are reversed. Q22 flat side left to right is D G S. Q23 flat side left to right is E B C

TIS58 Q22
D 2.4V
G 1V signal 88mV
S 10.6V signal 1.2V

TIS98 Q23
E 23.7V signal 6mV
B 10.6V signal 1.2V
C 11.3V

Supply V seem to match schematic.

[Helmholtz]

D voltage should be higher than S. C voltage should be higher than E.

[misterc57]

D voltage should be higher than S. C voltage should be higher than E.

So they are both installed backwards? Or am I reading it backwards?

[Helmholtz]

With the BJT installed backwards, the circuit could never have worked.

Collector must connect to supply node B (if schematic is correct).