Tremoverb FX Loop not passing any wet signal

[thinskin57]

for some reason, my tverb's fx loop won't pass any wet signal when i put a processor into it. the problem isn't the processor, as i put it into the loop of another amp and it performed perfectly. (same cables too) my cables are all routed correctly. any ideas? i've got the send and mix knobs of the loop both set to noon. selector set to red & orange. not sure if it's supposed to do this or not, but when i turn the mix knob past noon it starts to attenuate the amp's volume. if i dime it completely, it completely kills all volume. very strange to me. hopefully something simple?

 

[94Tremoverb]

If you're sure you have it connected up correctly, it's most likely the Send LDR that's dead. (LDR14 on the schematic.) Test it by taking a cable from the Send jack to any other amp and see if you can get signal to it when the loop is active - if not, it's the LDR. Using a plain cable in the loop won't test it because the signal will still get through via the Mix pot even if the LDR is dead.

If the FX unit isn't receiving any signal, its output will look like a short to the amp (if it has a low enough impedance, which most do), so turning the Mix up all the way will mute the signal. But do check again that you have got everything connected up right!

If this is the cause, you should be able to fix it by connecting the send jack directly to the 0% end of the Mix pot with a wire, bypassing the LDR. I can't really see a reason why it's necessary to switch the Send side of the loop at all, since LDR15 switches the Return side (and LDR16 the bypass) and the loop should still work properly.

 

[thinskin57]

thanks 94Tremoverb. here's what happened- i engaged the loop and went from the fx send of the tverb to the front end of another amp and got sound. THEN, i went from the tverb fx send, to a boss octave pedal, to the other amp's front end once again. i got a signal, AND the octave effect worked too. so at this point i pulled the cable out of the front of the other amp and patched it back to the fx return of my tverb. NO effect. dry signal only. seems like an issue with the return jack somehow? what do you think?

 

[94Tremoverb]

Yes, I think it has to be - there is no component between the jack and the Mix pot, so if it works with the Mix turned down and mutes the signal with it turned up, and the same cable will correctly pass signal to another amp, the short must be in the jack itself. That was a very thorough test and you've eliminated every other possibility.

Sometimes the spring contacts get bent out of shape and can short against one of the others, or the ground - it often seems to be caused by undersized or badly shaped far-east-made plugs which can grab the contact and pull it back too far.

 

[thinskin57]

thanks again. i'm off to pull my chassis! hopefully i'll be back w/a "success" story.

 

[thinskin57]

94Tremoverb- Success!! You're going to laugh here. pulled the chassis and removed the return jack. i get in my car to go to the local electronics parts store. i'm sitting at a red light and i look at the jack and notice something- mesa had soldered this thing to the SLEEVE connection of the jack! so i make a u-turn, go back home, resolder correctly, and i'm back in business! i purchased this amp from the original owner and now i know he wasn't lying when he said he never used the fx loop. anyway- 1,000 thanks to you for all your tverb related posts here over the last few months. i've learned a lot about this amp from you.