Mesa Boogie Express no reverb?

koss59

I have an express combo and the reverb isn’t working, turning up the knobs introduces hiss and some top end but no reverb.
Could this be a valve?

BlueStrat

Could be the revrb tank has a problem? Check the connections on the thin black and white wires at the side of the cabinet. Else i think its a 12ax7

ICBM

Much more likely to be the reverb tank. First check the RCA plugs at both ends of the cables, but if it's not that then probably one of the coil wires has broken. If you're very lucky it's between the jack and the coil, in which case you can resolder it, but more commonly with modern Accutronics tanks, it's on the little red plastic coil former where the very fine coil wires go over the edge of the bobbin. If you're incredibly careful and patient it can *sometimes* be fixed by soldering on a new strand of wire, but even with experience sometimes they just resist all attempts.

A new tank isn't too expensive, but you would be best to avoid Accutronics or Belton as they share this design and it's just a matter of time before it breaks again - the problem is actually caused by the weight of the plastic push-connector jiggling about and flexing the pins, so if you do get one I prefer to cut the connector off and solder the wires to the pins as close as possible to the bobbin as a pre-emptive measure. TAD/MOD/Ruby tanks don't have this design fault, the wires are run straight into the coil, so they don't break like this. (Original vintage Accutronics ones don't either.)

koss59

Great advice thank you both 

koss59

@ICBM ; so I’ve taken the tank out, it can still make the crashing noice through the amp.
When I unplug the RCA from the tank the toppy sound and hiss disappears.
I’m guessing this all points to a broken tank.
It seems to be made by Sound Enhancements Inc

ICBM

koss59 said:

@ICBM ; so I’ve taken the tank out, it can still make the crashing noice through the amp.
When I unplug the RCA from the tank the toppy sound and hiss disappears.
I’m guessing this all points to a broken tank.
It seems to be made by Sound Enhancements Inc

That's not quite what I would expect... if the tank is broken you will normally not get a crash or noise. (They usually break at the output end.)

Try connecting just the thick grey cable to the output end (where it normally goes), leaving the thin wire loose - do you get crash, or hiss, or both?

Then connect the same cable to the input end and repeat.

koss59

Thick wire left in and thin removed gives a faint crashing noise to the tank.
That cable plugged into the other end of the tank gives no noise.

Plugging in the thin wire creates all the noise and gives a loud crashing when tapped.

ICBM

That's quite odd... normally, if the end the grey cable is plugged into is working you should get normal volume of crash and noise. If it's broken you should get silence or some hum, but no crash or hiss.

I'm wondering if a ground connection has failed in the tank - the send (the thin cable) is not grounded, it relies on the ground in the return (thick) cable to complete the circuit.

koss59

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