Reverb on a 1982 Musicman 112RD50 not working

[Schneiderman]

The reverb never worked since I got the amp, and I went for a while without bothering with it. If I tapped the tank, spring noise came out loud and clear like you would expect, but there was never any reverb in the guitar signal. Last week I took the tank out and it had a broken spring. I ordered a replacement from accutronics, using the stock specs from the original unit, got it this morning, hooked it up... same problem. Loud spring noise when I tap on it, but no reverb in the guitar signal. Doesn't matter what channel it's on or where the reverb knob is set to.

Any ideas?

[rexindigo]

I own a 110rd50, the reverb tank is fixed on the bottom of the cab.
ist connected to the chassis via two plugs,they are right besidethe two plugs for the footswitch reverb and channel-switch, all four plugs look absolutely identical
Several ideas:
- a former owner has plugged them in the wrong way, a.) into the footswitch plugs or b.) with the wrong polarity (if there is a Polarity with Reverb tanks)
- they are plugged in the wrong way and since the footswitch controlles the reverb its permanently off
- The footswitch is missing and reverb is permanently of without something plugged in (My Bass Player came up with an old Fender Bandmaster and told me that the only thing that didnt work was the tremolo unit... Shortening the Tremolo Footswitch Plug made it work instantly....)

[Schneiderman]

Thanks for the help but the footswitch is installed and works properly, and the reverb wires appear to be installed correctly. To be sure I did switch the wires at the reverb, when I did this there was no response from the reverb at all.

The footswitch does appear to turn the reverb on and off, since I can turn it on and the springs will make noise or turn it off and then the springs don't make noise. But in any case, I'm still not getting reverb with the guitar signal.

[52 Bill]

I'm still not getting reverb with the guitar signal.

The first thing to do is double check your new tank. Pay close attention to the in and out jacks. Are the jacks exactly the same on both tanks? The difference here may be the ground connection. Are both jacks insulated or un-insulated or a combination of the two.

Did you check the cables? If they are ok, then you will need to work on the drive circuit inside the amp.

Do you have a copy of the schematic for your amp? The reverb is driven by an opamp. If you have the schematic it will be easier to find, but if you trace back from the RCA jack that goes to the input of the tank, you will know which IC is the reverb driver.

Measure the voltages referenced to ground, on the pins of the chip. Compare these measurements with the voltages listed on the schematic. Basically, you should only have voltages on the + and - supply pins, around + and - 15 to 18vdc. There should be little or no voltage on any of the input or output pins.

If you do have voltage on the input or output pins, you will need to replace the chip. If you are lucky, the chip will be socketed and easy to replace, if not then it will require the removal of the circuit board to unsolder and replace the chip.

Hope this helps.

[Schneiderman]

Thanks 52 Bill, I don't have a schematic and don't know where to get one but I'll get looking and try to figure this out. If anyone has any more advice let me know.

[52 Bill]

Thanks 52 Bill, I don't have a schematic and don't know where to get one but I'll get looking and try to figure this out. If anyone has any more advice let me know.

Steve Ahola has one on the blue guitar site.
http://www.blueguitar.org/new/schem/...m_rd50_mod.pdf

And after checking it out, your reverb is not driven by an opamp, but by a two stage transisitor driver. You will need to check Q1 and Q2 along with the related circuit parts.

[baddog]

I had a simular problem with my Crate Vc50 and it turned out to be a bad tank and the IC chip was also bad.