Question on reverb tank transducers

[glebert]

I have a 1983 Roland JC-120 for which the reverb tank is acting up. The thing I don't understand is that if I measure the resistance of the output with it flat it reads open, but if I rotate it slightly I will get 200 ohms, which is appropriate for this tank from what I can find. I've had something similar on a Fender amp unit as well. Is this a broken lead in the transducer or what?

[xtian]

Yes, sounds broken, or at least intermittent. You might try resoldering the connections. Worst case, replacement tanks are inexpensive (though I don’t know exactly what’s in that Roland).

[J M Fahey]

if I measure the resistance of the output with it flat it reads open, but if I rotate it slightly I will get 200 ohms

Sorry, don´t understand what you mean.
You measure RCA "out" connector resistance from center to body and you get open, then rotate full tank and get 200 ohms?
If so, open tank and inspect it visually, under good light and using a loupe if necessary, one of the thin wires connecting bobbin to connector may be loose.
Easy peasy to solve.

Cable must not be tight but have some slack, inrernal reverb tray floats on springs and moves all over the place.
That´s why (eventually) wires flex and crack.

[glebert]

Hmmn, tried to post an update last night and for whatever reason it didn't post. It was indeed an intermittent solder joint right where the small wires connect to the RCA jack. Apparently the beautiful girls in Milton, WI had the temperature too low in their climate controlled environment. Kind of amazing that such a fine wire could move at all during rotation. Now I get a good sproing when I tap the tank, but alas something else is still wrong, no reverb for signal (or maybe very, very weak reverb). Next stop: input side of tank (which ohm'd out OK but should probably reflow that too). I don't know if I have another tank of appropriate input/output impedance to swap in, but if I do I will try that too.

[J M Fahey]

If it "ohm´d" fine then tank IS fine, no need to replace it for testing.

Find why there is no drive signal instead.