Guild 98RT: Trem circtuit not working

[Jonny toetags]

Update:
The trem is dead again.
Same symptoms: you can hear the trem for a split second when you engage the switch....then nothing

[Jonny toetags]

Still trying to figure this one out.
I'm changed all electrolytics on the board
Resistor have tested to spec.
I've changed the caps in the trem circuit.
I tried bypassing the footswitch and hardwiring the connection.
All I have to go on is the fact that when I press the switch, I hear the effect for a split second.
If I make a change with the 'strength' knob, it is heard during that split second.

[Wes]

So C12, 14, and 15 are new? Try a different tube? R10 one of the resistors you tested as ok?

I recall, once, when I had this issue- I changed out one of .05/.047 caps to a .022 and it sustained.
You've got new ones in there now, won't hurt to try a substitution.

[Jonny toetags]

So C12, 14, and 15 are new? Try a different tube? R10 one of the resistors you tested as ok?

I recall, once, when I had this issue- I changed out one of .05/.047 caps to a .022 and it sustained.
You've got new ones in there now, won't hurt to try a substitution.

Yes, C12-14-15 are .047's and C16 is a new electrolytic (25uF)
C13 was changed to a new .1

[Jonny toetags]

I tried a few different tubes, same thing.
So I decided to try a different cap. I put a .022 in C15...tried the amp and noticed slight improvement: basically trem is on the weak side, but it's noticeable.
I tried a second .022 and then the trem was dead again. I removed and put the .047 and the trem was dead as well.
Put all the original caps in and trem was back but very weak...like when i first put the .022 in.

[Enzo]

Amy trem has two parts - an oscillator or LFO, and an interface. You are swapping parts then listening, but that doesn't tell us which half of the system has the problem.

First the LFO. With the switch on or the cathode resistor jumped to ground, do you measure about 1.2k to ground from pin 3 of the tube? With power on, is ther a large AC signal at the plate, pin 2? and on the other side of the 0.1uf cap? Power off, do you read about 540k from pin 5 to pin 5 of the two power tubes? And half that to the intensity control wiper from each pin 5?

Eunning, is that LFO signal on the top leg of the pot? The wiper when all the way up? At the junction of R29 and R34?

[Jonny toetags]

Amy trem has two parts - an oscillator or LFO, and an interface. You are swapping parts then listening, but that doesn't tell us which half of the system has the problem.

First the LFO. With the switch on or the cathode resistor jumped to ground, do you measure about 1.2k to ground from pin 3 of the tube? With power on, is ther a large AC signal at the plate, pin 2? and on the other side of the 0.1uf cap? Power off, do you read about 540k from pin 5 to pin 5 of the two power tubes? And half that to the intensity control wiper from each pin 5?

Eunning, is that LFO signal on the top leg of the pot? The wiper when all the way up? At the junction of R29 and R34?

Here's a few readings:
-couldnt get a reading from pin 3
-with trem on, V1: pin2: 109VDCto 130VDC - pin5: 140VDC
V2: pin2:65V - pin5: 65VDC
-amp off: pin 5 to 5 between powertubes: 605K
-otherside of .1 cap: 109-130VDC

[Enzo]

What does couldn;t get a reading mean? Couldn;t get your meter probe onto the pin? If you got the probe on the pin, unless your meter was turned off, you got some sort of reading, I'll wager.

Look at the schematic, pin 3 is the cathode, and when the switch is on, there is a 1.2k resistor from there to ground. I want to verify that circuit. By measuring resistance from pin 3 to ground, we are checking not only the resistor but the connections to it. The amp must be off to make resistance readings.


Pin 5 to 5 on the power tubes looks OK, but how about to ground from each? Turn the intensity control to zero for this. I now expect about 300k. If you get that, then turn the intensity control to the max. Do you now get about 1.3 meg?

C13 is that 0.1uf from pin 2 of V1 to the top of the intensity control. With the amp ON and the trem OFF, so you still get the same DC voltages on both sides of that cap? In that setting, I expect about 300v on the pin 2 side and zero on the control side.


By the way, if you have a DC reading that is moving 109-130-109-130 ongoing, it looks like your LFO might be running.

[Jonny toetags]

What does couldn;t get a reading mean? Couldn;t get your meter probe onto the pin? If you got the probe on the pin, unless your meter was turned off, you got some sort of reading, I'll wager.

Look at the schematic, pin 3 is the cathode, and when the switch is on, there is a 1.2k resistor from there to ground. I want to verify that circuit. By measuring resistance from pin 3 to ground, we are checking not only the resistor but the connections to it. The amp must be off to make resistance readings.


Pin 5 to 5 on the power tubes looks OK, but how about to ground from each? Turn the intensity control to zero for this. I now expect about 300k. If you get that, then turn the intensity control to the max. Do you now get about 1.3 meg?

C13 is that 0.1uf from pin 2 of V1 to the top of the intensity control. With the amp ON and the trem OFF, so you still get the same DC voltages on both sides of that cap? In that setting, I expect about 300v on the pin 2 side and zero on the control side.


By the way, if you have a DC reading that is moving 109-130-109-130 ongoing, it looks like your LFO might be running.

Pin 3 to ground measures at exactly 1k
pin 5 of the powertubes, trem intensity at 0, reading is 300k. as i start to increase the intensity pot, meter just shows 0.0 all the way up and i get a motorboating sound.

C13, amp on, trem off: 300V on the side facing the controls, 0V on the side facing the tubes

[Enzo]

A motorboating sound? The amp needs to be off when taking resistance readings.

[Jonny toetags]

A motorboating sound? The amp needs to be off when taking resistance readings.

280k with the intensity at 0....goes all the way to 1.03meg with int at max