Fender Blues Deluxe FX loop not working....

guitarnut_1

Member
Messages
1,978
I wanted to connect a delay in the preamp out - power amp in loop of my Fender BD and there was no signal at all. I thought the effect itself was broken, then I connected the pre amp out - power amp in DIRECTLY with a patch cable and still NO sound. This means the circuit between pre amp OUT and power amp IN is somewhere broken, right?

Otherwise the amp is working flawlessly if you don't use this FX loop. I suppose some of the preamp-poweramp (IN/OUT) jacks are either broken or there is a bald solder join.

I also opened up the amp to measure the circuit between pre amp out and power amp in, but the jacks are mounted directly to the PCB. Are they soldered or do they plug in and out of the PCB? I am not really willing to take all the pots off in order to dismount the PCB and peek at the other side of the board. Has anyone changed any jacks on this amp?

If the PCB needs to be taken off, I will probably leave it as is.... I have been using this amp for years and never had any need for an FX loop.

Thanks
 

tresspassor

Member
Messages
1,133
You can easily determine which connector it might be. Plug your guitar directly into the power amp in. No worky, then it's probably that one. Got a tuner pedal or another amp? Connect one of them to the preamp out. Either way, a can of deoxit will probably be your best friend for this issue.
 

Jeff Gehring

Gold Supporting Member
Messages
6,213
Or you may have a problem with the U1A op amp, as it is only used when using the pre-amp out jack. Do you get any signal if you just run a cable from the BD pre-amp out jack to another amp's input (with either an open plug in the power amp in jack, or the Blues Deluxe dummy loaded)?
 

guitarnut_1

Member
Messages
1,978
You can easily determine which connector it might be. Plug your guitar directly into the power amp in. No worky, then it's probably that one. Got a tuner pedal or another amp? Connect one of them to the preamp out. Either way, a can of deoxit will probably be your best friend for this issue.
Thanks for your input guys!

signal gets lost after the preamp out. Guitar plugged straight into the power amp plays fine!

Or you may have a problem with the U1A op amp, as it is only used when using the pre-amp out jack. Do you get any signal if you just run a cable from the BD pre-amp out jack to another amp's input (with either an open plug in the power amp in jack, or the Blues Deluxe dummy loaded)?
guitar plugged in normally and a tuner attached at preamp out jack - tuner gets no signal.

If I try a contact spray, can I spray this directly into the jack or would I still need to take the PCB off and check the lugs of the preamp OUT jack?

Cheers
 

Jeff Gehring

Gold Supporting Member
Messages
6,213
signal gets lost after the preamp out. Guitar plugged straight into the power amp plays fine!

guitar plugged in normally and a tuner attached at preamp out jack - tuner gets no signal.
Based on this information, you probably will NOT fix it by cleaning the send jack. What you are saying is that:
  • Normal operation (nothing in the loop at all) is fine.
  • With a tuner in the loop, you get nothing out, and the tuner shows it is NOT receiving signal from the send jack.
As you can see from the schematic fragment below, the send jack is NOT a switching jack. All the switching is done on the power amp in jack, which is operating fine.
The ONLY time op amp U1A comes into play is when you use the preamp out jack. It is not in use (although it still receives signal) during normal operation.
Looks like a problem with U1A on the face of things... or maybe a failed solder connection to the preamp out jack.

View media item 51722
 

guitarnut_1

Member
Messages
1,978
Ok, thanks Jeff!

The tuner was not "in the loop", it has only ONE input jack, and no OUT; tuner hooked to the preamp OUT (tuner gets NO signal); the guitar plugged into the normal IN jack - signal OK; poweramp IN NOT connected.

Poweramp IN signal is OK and alive (IF guitar plugged straight into it)!

I don't think I can repair this without taking the pots and the PCB off. That's the only way to check solders and things.

Cheers
Peter
 
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