Reverb not working in a Fender Blues Jr.

[72Blazer]

Reverb not working.  When I put a knock on the reverb tank there is no sound like I would expect.  In fact, I temporarily tried a known working reverb tank and I get the expected sound of the springs moving but the reverb effect is not present when strumming the guitar.  I do not see any obvious damage to components on the circuit board.  Any suggestions?

Vr
J.

[72Blazer]

Here is the schematic I found here on the this site.

[PRR]

> put a knock on the reverb tank there is no sound like I would expect.

Bad pickup coil. Are there any Ohms in it? Have you mixed-up the 4Ω semd and the 1K pickup?

> I temporarily tried a known working reverb tank and I get the expected sound of the springs moving but the reverb effect is not present when strumming

Is this "expected sound" in the speaker or coming out of the tank walls?

[Latole]

Use a scope
Or it is this OP  ?

[72Blazer]

The springs moving made sound through the speaker, but guitar signal sound has no reverb effect.  Hopefully that makes better sense.  Thanks

[thetragichero]

check reverb driver stage. as mentioned, a scope would be supremely helpful here. trace back from reverb send and see where the signal dies

[glass54]

Dear 72Blazer,
Quick Check  :
Vol at 1/4 rotation, Tones at 50%, MV at 1/4 rotation, Reverb pot start at 1/4 rotation, join tips of RCA with alligator clip, strum guitar and you should be able to use Reverb Level control as another "Volume" (Note: RCAs removed from Tank)
From what you have described (in post #4), I suspect the pickup coil as PRR has eluded to. It's unusual for the 4560 Op Amp to go faulty BUT not impossible and more likely the tank. Double check the coil wires to RCA connectors, as these can fracture/break.
Trust this helps, kind Regards
Mirek 

[72Blazer]

Thanks Mirek/all.  I'll give that a go in the morning.

Vr
J.

[jordan86]

I had a similar issue recently on a 2006 BJ. There was a connection inside the tank that broke. Cheap tiny wire and a crap plastic connector. Had to toss the connector and solder wires directly on.

[Latole]

Test reverb recovery circuit as Sluckey explain here ;

https://el34world.com/Forum/index.php?topic=27336.0

" Try one more thing before you order a replacement tank. Plug your guitar into the reverb return jack using adapters, or gator clip leads and a phone jack. It may be easier to just temporarily replace the phono jack with a phone jack. You should be able to play guitar through the amp (not loudly) and the reverb pot will act as a volume control. If this test passes then get another tank. "

-Sluckey

[72Blazer]

Iverified the wires to the coil wires to RCA connectors are good.  I then used alligator clips to connect the two tips of the RCA connectors as Mirek instructed.  The reverb pot did act as a volume.  I need a new reverb tank - correct?

Vr
j.

[thetragichero]

measure dc resistance between rca jack tip and sleeve (for lack of better nomenclature) on the reverb tank input and output

[72Blazer]

Output:  1.6M Ohms
Input:  58 ohms

[PRR]

> Output:  1.6M Ohms

Should be a few K at most.

Look inside for leads broken at the RCA or at the coil.

[72Blazer]

PRR,

Both green and black wires (output and input side) have solid connection and continuty.  This includes inside the little plastic connector tabs that the wires feed. 

I rechecked and OHMs:

Output:  1.2M Ohms (this time)
Input:  58 ohms

Lastly, using a deluxe reverb tank/NOT correct blues Jr type, when I temporarily connected it up to this amp--it DID NOT deliver the reverb effect out the speaker either when strumming the guitar.  I don't know if this is a clue or if it is even relevant since it is not the correct type of reverb tank.  Appreciate the T/S efforts.

Thanks again.

[Latole]

Shake that tank to ear.

[sluckey]

I don't think that DR tank will work in your BJ circuit. Read reply #9 and test the recover circuit. If you can hear guitar then the recovery circuit should be OK.

[thetragichero]

deluxe reverb tank would have an input impedance of 8ohms. your blue junior uses a solid state reverb driver/recovery stage, so the input impedance is on the order of several hundred or a few thousand ohms. a 4560 isn't capable of driving an impedance that low (quick google suggest maybe as low as 400 ohms). you'd need something like an lm386 to have any hope of driving the deluxe reverb tank and even that would likely be quite weak (also the pcb isn't setup for lm386, yadda yadda)

follow the suggestions of the folks here, but your > 1M on the tank output leads me to believe it's either a bum transducer or there's an issue between the rca jack and the coil (unhook the molex connector and take a resistance reading directly at the pins to the coil)

[72Blazer]

Followed reply 9 and guitar signal heard/adjustable with reverb pot.  Understand my FDR tank is not suitable.  Ordering the correct replacement tank from MOJO.

Thank all.

Vr
J.

[PRR]

> Output:  1.6M Ohms
> Output:  1.2M Ohms (this time)

1.2, 1.6, all the same.... it CAN'T be MEGs, you are reading damp dust on the insulation. Or maybe your finger?

[72Blazer]

PRR I stand corrected.

I disconnected the molex connectors and measured the pins on the coil as instructed in reply #17:

Output was OL
Input side: 58 Ohms

Does this now confirm the reverb tank is inop?

Vr
J.

[Latole]

Yes if your reading are good

[72Blazer]

Ok then.  I learned a little bit about reverb tanks in the process. 
Thanks again everyone.
Vr
J.

[Latole]

All useful to know about reverb tanks.

https://www.amplifiedparts.com/tech-articles/spring-reverb-tanks-explained-and-compared

[72Blazer]

Thanks Latole-even a section on this particular reverb tank for FB Jr.  Good stuff.
Vr
J.

[Latole]

http://www.accutronicsreverb.com.


I have already seen on the Accutronics site (Accu Bel Sound) that they also mention the measured ohms (DC ohms) in addition to the impedance. I don't have access to this information anymore because it requires the FlashPlayer plug-in.

[72Blazer]

Just thought I'd let y'all know I put in the new replacement reverb tank tonite and she's good to go now.  My jam buddy will be pleased it's ops normal now.  Again-I appreciate the troubleshooting tips.

Vr
J.