Fender Twin Amp Tremolo not working

[gretschman2112]

I am trying to figure out why the tremolo on my Twin isn't working. I'm not sure if it ever worked because I never use it. I purchased it new in 2005.

I have the foot pedal plugged in, and the tremolo LED will turn on and off when I switch it, but nothing changes. I have swapped out tubes to see if it was a bad tube, but no luck. I have taken the chassis out and looked for anything obvious. My voltages seem to be on the high side with reference to the schematic, but I can't seem to track down the problem.

Does anyone have any info about this problem?

[txstrat]

Welcome to the forum.
Since the LED is working I would assume the LDR module is OK unless the
1. LDR itself has gone bad.
2. There might be an open resistor/capacitor in the tremolo circuit or the
3. controls are faulty.
Also check all the solder joints in this area of the circuit.
And be aware of the lethal voltages inside the chassis.

[hollisdevillo]

and since you have never used it, although it seems obvious, we've all been there before, check if the pan is actually plugged in. and if your controls are set right. otherwise, follow txstrat's advice, either LDR or cap in that stage. and definitely loose joints or broken wire.

[Twist]

Are you referring to the "Twin amp" or the "Twin Reverb"? I don't think the newer "Twin Amp" uses an LDR. I believe it generates a signal onto the bias circuit.

[txstrat]

Are you referring to the "Twin amp" or the "Twin Reverb"? I don't think the newer "Twin Amp" uses an LDR. I believe it generates a signal onto the bias circuit.

That's what I thought in the first place too but there would be no flashing LED if it was the bias trem.

[Enzo]

The LED on the footswitch is going on or off when he stomps the switch. The Twin AMp does rock the bias, but that is not related to the LED indicator.

You bought the amp new in 2005? At least in the USA, there is a 5 year warranty on the amp, so take it in for warranty service - you should have a year left.

hollis, are you having a senior moment? Tremolo pan?

But as to the problem itself... The LED is turned on and off by the stomp switch in parallel with it. That doesn;t tell us if the control signal is actually going anywhere in the amp. You need to verify that the output of U4 pin 7 is toggling from +15VDC to -15VDC as the trem is turned on. If that pin doesn;t move, then the trem circuit won;t either.

If that is happening, then V6 is the trem tube. Is there a big LFO signal at pin 6? If not then the tube isn;t oscillating. First suspect is the trem mute transistor the U4 controls - Q102. If that is stuck on, the trem is stuck off.

If there is a large LFO signal there, then is it on the cathode follower at pin 3? And if it is there, then is it at the tops of the intensity controls?

[hollisdevillo]

hollis, are you having a senior moment? Tremolo pan?

hahaha, yeah. i really put my mouth in my foot on this one.

[gretschman2112]

Thanks, I think I'll look into the warranty service. I'll probably have to take on a trip to get someone to fix it, but it should be worth it.
And yeah it a "Twin" amp, and uses tube bias for the tremolo to work. I thought it would be something easy to find, but I can't seem to track it down. It looks like the oscillator is working but somewhere in the path it's not getting through.

[Enzo]

How did you determine the oscillator was running?

[gretschman2112]

Well I can tell it is turning on and off by measuring the voltages. However, I don't have a scope to actually see a waveform so it is possible that it is not working. But what I can tell from my DMM is that it is at least turning on/off.

The only thing is, there is no change the the output level when it is switched on/off.

[Enzo]

OK, voltmeter works. As long as you can see it on the meter, we don;t really care about acfuracy, all we want is to get the LFO to where it needs to go. SO follow it from the plate of the trem tube through the caps over to the intensity controls. See if you can find a spot in the path where it disappears.

[gretschman2112]

Well I took it into the shop since it is still under warranty. I should hear back in a couple days. I completely forgot about the 5 year warranty. Thanks

[garytronix]

Hey gretschman2112,
What did the shop do to fix your Twin Tremolo problem. I have the same voodo.

Your help would be appreciated,
garytronix

[midnitecruzer]

hi all--

New to the forum, but found exactly what I was looking for in this thread. Anyway, my twin seems to have suffered the same problem. Well, after checking what Enzo suggested, U4 pin 7 is toggling between -15 and +15, V6 pin 6 has the LFO functioning and is moving in accordance to where the speed pot is set, for pin 3 I'm not sure what I'm seeing on the scope, but it's not nearly as large in amplitude as the LFO. Intensity seems to do a little something with it when I moved it. I'm sort of on the newer side at this one, and just not sure what to do from here. I did however replace Q103. Any help would be fantastic. gretschman2112... any word on what the tech did?

[midnitecruzer]

Ok. Here's some more measurements. Trem off as written in the schematic.
My readings:
V6
pin3= +317Vdc
pin6= +307Vdc
pin8= -.6mVdc

What Fender claims it should be:
pin3 +255
pin6 +256
pin8 +4mV