Fender Blues Deluxe RI Reverb off.. inop.

[Indyryder02]

Hello wise ones. I ask kindly for your guidance again.

Initially, amp was cutting out. Bad solder joints, due to the common low voltage section resistors and diodes against the board. Rebuilt that section with parts flown away from the board as usual.
15v supplies are good. And on all ICs

Amp has no reverb. TP36 is + 15.6. Should be - for Reverb on. Right? Unless this too is only with the footswitch? If so that’s just throwing me off.

Audio TP’s. Are good before the reverb tank. And 0mv after. Signal present at output of tank. Cable good. As soon as you plug cable to tank it pulls the signal down.
is Q2 on? And it’s turned on by U3? Or am I way off in the weeds again? I feel like I am! Haha

I’d like to know how U3 switches pin 1 from + to -
So I can understand what it needs or is missing.
And I’m researching how the JFET switches on currently.

To confuse things more. I can hear, from the speaker. The tank crash when I shake it. So like the return is fine.
Which really doesn’t add up with the other info.

Checked continuity of the shield on the input cable to
WJ2 and U2-pin 2 as I read in a post from Enzo, that would kill the driver. But it checked good.
I’ve replaced both U2 and U3 without change.

Thanks in advance!!

[mikeydee77]

Recommend checking both + and - 15v supplies. Bit of a weak spot.

[Indyryder02]

Recommend checking both + and - 15v supplies. Bit of a weak spot.

They’re fine.

[Jon Snell]

To recap;
Signal is as expected up to he pan, nothing after the pan.
Is the pan correct with the cprrect type fitted.
4560 chips are current protected so difficult to 'kill'.
Insert a signal on pin 5 of U2-B what is on pin 7.

Why are you confusing yourself by looking at the Fets? If Q2 were faulty, there would still be signal on the reverb pot.

[Indyryder02]

Doh! It is not the correct pan. I had even considered this earlier but moved past the idea due to TP36 showing reverb off condition. (If I’m correct on that?) I don’t have the correct one on hand to try. But would that be enough to have no reverb at all? If it’s just the pan I’m gonna have to kick myself for sure!!

And the owner never mentioned the reverb not working. Now after discussion.. it apparently has not worked for some time. But it used to. Thinks he bought it new.. with this MoD tank in it. (Has one installed for an original blues deluxe not the reissue that this one is).
And thinks the reverb slowly went out a year or two ago…. So none of that is adding up much..
So it may have a combination of issues. Definitely the wrong tank. But TP36 still makes me think there’s more than just a tank swap. If TP36 is in reverb off condition. Is some other fault tricking it to be off? And when it’s off, it just turns Q2 on to mute it? If that’s the case, why can hear hear it crash when I shake the pan?
I could really use some help better understanding this part of the circuit. Thanks in advance.

[g1]

Double check your TP36 voltage, compare with TP30. Both should be showing negative during normal operation with no footswitch.
The original tank was 150 ohm input impedance, the re-issue is 600. Do you have a 4BB tank in there instead of the 4EB ? If so, the reverb would be much weaker, but I don't think it would completely kill it.

[Indyryder02]

Hi G1! Glad to hear from you!
Yes, it’s a 4BB.

TP36 +15.4
TP30 -13.6

[g1]

Well that's very strange. If the Q2 is on, it should be muting the reverb crash when you shake the tank. But maybe it is way quieter than it should be.
Check TP34 and TP35 and compare results with schematic notes.

[Indyryder02]

Yes. It’s not a super loud crash by any means. Just audible.
I noticed what appears to be an error on the schematic for TP34. On the PCB layout it points to one end of D26, but ok the schematic it’s between U3 pin 3 and R92
so I have -17 on pin 3…. And - .5 where TP34 is shown on the end of D26..
TP35 is - 1.2v

[g1]

What do you have at pin 2 ?

[Indyryder02]

-1.3

[Jon Snell]

If you are using a MOJO pan, Red and White are reversed!
You state you have slight noise when you thump the pan, stroking the springs should be loud.
Don't confuse yourself again by looking at the switching! Look for signal on the reverb pot. If you have signal there, the reverb is working.
Could't be a simpler test. It will save you so much effort.
When you have signal on the pot that is the time to check out the switching.

[Indyryder02]

As for signal after the pan and on the pot.
TP20 780mv
TP21 1.9mv
TP22 132mv

with the scope I can see I do have signal at both sides of R103. Although it’s less than normal likely due to the wrong tank. I am able to adjust the signal on the pot side of R22 , via the pot. But at the JFET side there is nothing.

[g1]

-1.3

So pin 2, -1.3V, pin 3, -17. Pin 3 is the non-inverting (+) input of the op amp. If it is more negative than pin 2, the output (pin 1) should go negative (but you have +15V).
Is it definitely the correct IC and inserted correctly?

[Indyryder02]

Yes. I believe so. I changed the original 4560.
It was a BA 4560 as was U2. I replaced both with sockets. Then installed RC4560 ICs.
I’ve tried a couple different ones as well in case the replacement was bad for any reason.
I’ve checked all the surrounding components, in circuit. And they all seem to test good as well.
Thank you for explaining was causes the output to go negative. That’s still my biggest struggle is just understanding how those devices work exactly.