Fender Blues Deluxe reverb issue HELP ! I'm going insane here !!

[WillyK]

Ok Guys,
I need some help, Im loosing it here!
I have an original Blues deluxe amp that I bought from someone a while ago. When I bought it I was told it was having channel switching problems, other than that it worked fine . I met the guy in a parking lot and bought the amp ( I trusted him about the problems, Why you ask? because I'm an idiot, thats why! ) I got it home and found that someone has been into the amp and butchered it real good!! This poor thing has been through the ringer more hacked repairs than I have ever seen.
To shorten this up, I have everything working except the reverb. This must have been an issue with the old owner too, because the reverb control , the op amp and the pan has all been replaced.
Heres what happens : When you try to use the reverb, you get noise if you shake the pan, very faint but you can here it, the control does change the volume of the reverb but very very little, amp volume control has no affect , either channel , I checked the pan and control, they are both correct replacements an work. I replaced the op amp just in case, same problem, I have checked the rcas, they are both fine. I removed all 3 ribbon cables and rewired them ( Part of the repair to make it play at all) , that's fine. Tubes are fine. I'm going crazy I have traced out the circuit metered everything I can meter, 16 v and -16v are fine and present on the op amp .
Any Idea would really be appreciated as I just want to put it back together and play it ! I dont ask for alot out of life, just that my amp works!
Thanks in advance

[The Dude]

http://www.thetubestore.com/lib/thet...-Schematic.pdf

Fortunately, Fender is kind enough to give you test points and signal levels. Inject a test signal and follow the test points through the circuit. See where you lose it.

P.S. Welcome to the place!

[nevetslab]

Without getting into what hacks & mods were done to the reverb circuit, what reverb tank is installed? The Blues Jr, using just an op amp to drive the input of the tank, it needs to be a high input impedance tank. The circuit looks similar to the Hot Rod series, which calls out for an Accutronics 4EB3C1B tank, which is 600 ohm input and 2250 ohm output impedance. If you measure the DCR of the input and output of the tank that's installed, and the input measures 10 ohms or less, it's the wrong tank type. That would be one for a Twin Reverb or Deluxe Reverb, driven by a transformer, and is around 8 ohms input Z and 2250 ohms output Z..You'd never hear the reverb, as the op amp can't drive it. But, knocking the tank to make it splash, you should hear that even if it was the wrong input Z.

[52 Bill]

Welcome to the place.

The reverb is entirely solid state, all of the circuitry is based around IC U2. If you can hear the reverb springs rattle but only weakly, I'd check to see if there are any damaged traces around the return circuit.

If the reverb control was replaced check the continuity of the pc traces around the pot. The weak but working signal would lead me to believe that the signal is being lost somewhere after the reverb control.

Once the return circuit is working, you will need to test the drive side of the circuit. And just as important as the input impedance is the tank input jack must be isolated from the chassis, not grounded to the case.

[WillyK]

Thanks for the info so far guys, The reverb tank is a 4bb3c1b Which Is supposed to be the correct tank. It measures 150 Ohms and 2.25 k , I actually have a pair of these and swapped them out just in case, no luck , still not right.

As for the broken trace theory, I thought the same thing, I have metered traces till the board just looks like a mess and your head feels like its going to explode. No luck

[glebert]

Dumb question: when they hacked up the board did they rework it to the original reverb circuit or the reissue? Sounds like they may not have paid attention to the difference.

[WillyK]

Pretty much all of the really bad work involved the resistor / diode repair, (which apparently was in need or a dozen wires running everywhere for no good reason), an attempt at fixing the ribbon cables that made me look like super tech, and replacing the input jacks and yet again using a dozen wires , half of which weren't even soldered ! ,The reverb pot, and op amp replacement were the only thing that were soldered neatly, but you could see they definitely were replaced. The pot is the correct value and the op amp was a tl072 so that was good too.

[Enzo]

Do you HAVE a 4EB2C1B or 4EB3C1B reverb pan around? Try it if so. I know the schematic calls for a 4BB pan, but the drive circuit on that schematic is identical to the other circuits that require a 4EB pan. The drive is the difference between a 4BB and a 4EB. The outputs are the same in both pans, and that is the only place where the amp circuits differ, so ti really seems to my eyes that the schematic callout could be in error.

[g1]

I'd try just putting your thumb on the P4 return plug (without touching the ground).
Can you get a loud hum or is that weak too?

[WillyK]

I'd try just putting your thumb on the P4 return plug (without touching the ground).
Can you get a loud hum or is that weak too?

No,
If you touch the pin its very weak also.

[Tone Meister]

Do you HAVE a 4EB2C1B or 4EB3C1B reverb pan around? Try it if so. I know the schematic calls for a 4BB pan, but the drive circuit on that schematic is identical to the other circuits that require a 4EB pan. The drive is the difference between a 4BB and a 4EB. The outputs are the same in both pans, and that is the only place where the amp circuits differ, so ti really seems to my eyes that the schematic callout could be in error.

No,
If you touch the pin its very weak also.

I second trying the 4EB tank. If you don't follow any other advice here, Enzo is the one you should listen to.

Welcome to the place ...