Fender Deluxe 112 Plus Buzzing/Squeal in Reverb

[misterc57]

With the reverb tank completely disconnected I get buzzing noise (no squeal) as I rotate the reverb pot from 1 to 10, getting very loud as I go up the scale. This happens even with the volume pot set at zero.

Right now I have everything on the bench outside the cabinet; Tank, chassis, speaker. I have never done this before but I made a video. Hope it helps diagnose the issue. Sorry for the shaking and poor narration, it is my first time. Volume pot is set at zero during the video

...

[g1]

I didn't hear any squeal in the video? Has something changed?

[misterc57]

Yes the squeal went away now that everything is on the bench.

[nickb]

The pan p/n is 8EB2C1B. The pan output connector shell should be connected to the pan chassis.

accutronics products and specifications

[g1]

Check that resistance again, pan output jack ground to pan chassis. Maybe movement got it to reconnect and that has made the squeal go away?

[misterc57]

The connectors at the pan itself are isolated from the pan chassis. Remember that this reverb pan is working fine in another amp.

The pan output shield wire P4 at the amp chassis is connected to chassis ground (as it should be). It reads 26 ohms to ground.

[g1]

Different model's of amps require different tank grounding schemes. It could be the correct tank for the other amp and incorrect for this one.
The tank specified for this amp should not have an isolated output jack, so I don't think you have a 8EB2C1B. The "c" is the grounding designator, could it be another letter there?
Regardless, easy to check/modify. Get it back to the way it way when it squealed, short the tank output jack ground to the tank shell.

[bsco]

g-one is right....the output rca cable is grounded to the output jack of the tank which is grounded to the metal tank itself....try and do a continunity check on that ground wire in the rca cable while you move the cable around and see if the connection goes open...even for an instant.....I have had a few blues juniors where the cables were intermittment and when you moved them around all sorts of crazy things happened...the other end of this cable is soldered to the board...hook one meter lead to the ground wire at the circuit board and then connect the other lead to the metal can....(you don't need the amp plugged into an outlet for this...make sure it is un-plugged)....also be aware that the transducers inside the tank itself are soldered to the rca jacks but probably go to a two pin plastic connector which in turn plugs into the transducer.....I have had these wires break where they are press fitted into the plastic connector itself....I am not saying that this is your problem but it sounds like an open ground??although it could be something else....however, since you now have everything removed from the cabinet and laid out on the bench, the squealing sound disappeared...and you were still getting the squealing sound when the chassis was out of the cabinet.....the tank and speaker were in the cabinet....so it could be possible of an intermittment connection....either in the tank itself,(although you tried the tank in another amp)or a bum connection in the rca patch cable...It could be at the end where the connector is located or it could be further back in the cable....By the way.....there is nothing wrong with your video...you did a good job.....



P.S. Sorry g-one...didn't see your last post....

[g1]

Where are you reading that 26 ohms to ground? There should be 0 ohms between the reverb output cable ground and circuit ground. Maybe this is related to your problem.

[misterc57]

I stand corrected. This tank is an 8EB2C1B and does have the output jack shield grounded to the tank. 0 ohms resistance.

Now this is getting more interesting. I also just noticed that the output cable for the reverb is soldered backwards on the amp board at P3 and P4. P4 which should be the shield is soldered to the tip. I thought I had discovered the problem, I flipped the connections with a second rca cable and jumpers. However the buzz is still there. ;-(

I have attached a pic of P1, P2, P3, P4. You can see in the picture that P3 and P4 are backwards. Please correct me if I am wrong.

[nickb]

It's wrong. That'll pick up all kinds of noise for sure. Sounds like you flipped the connections while the original wrong cable was still there. It would still pick up noise in that case.

[misterc57]

I am going to pull the board and correct the connections at P3 and P4. Will let you know what happens. Will not have a chance until tomorrow night.

Thanks

[bsco]

Is it possible that the previous owner had this amp repaired and this reverb cable was installed backwards at these connections?????? for reason's unknown.....and that is why the owner had sold it??? I have a good feeling that when you change these two connections around you might have your amp working...it seems that the rest of the circuitly is fine and the reverb is the only issue.....for what it's worth, I have had gear come to me which had been worked on before and stuff was installed wrong, backwards, wrong components, etc....even tin foil in place of fuses.....so don't be surprised that somebody else had looked at this before, connected the wires wrong, and then sent it back to the owner saying it couldn't be repaired....stranger things have happened....I am sure you will get it sorted out.......

[misterc57]

I swapped the cables on the board at P3 and P4. Buzzing noise went away. Woo hoo!!!

Now I discover the speaker is pretty much shot, rattling like crazy when you strike a hard note or low E.

Thanks to everyone for the great help on here!

This amp makes a good popping noise when it is shut off, any recommendations on fixing that?

Thanks again! MC

[bluesky6]

This amp makes a good popping noise when it is shut off, any recommendations on fixing that?

There's a thread on "Mods and Tweeks" on this. Putting a 0.1uF across the PT secondary helped for one person on his Princeton.

I found that changing the rectifier caps helped on two amps that I worked on. YMMV