Voltage regulator (OC3) question in 122......

[Chris Keyman]

Hi,
My 122 freaked out and went dead. Upon testing the tubes I discovered the OC3 voltage regulator was shorted out and useless. Can this thing going mad take out any other components like TRANSFORMERS etc? Should I just replace the tube and see if it works? BTW how can you test a transformer without turning the thing on? I used my fluke meter and I can tell you the capacitors seem ok. There are also no open resistors.
Chris

[jhelm_waterw]

Hi,
My 122 freaked out and went dead. Upon testing the tubes I discovered the OC3 voltage regulator was shorted out and useless. Can this thing going mad take out any other components like TRANSFORMERS etc? Should I just replace the tube and see if it works? BTW how can you test a transformer without turning the thing on? I used my fluke meter and I can tell you the capacitors seem ok. There are also no open resistors.
Chris

Hmm... it probably just went dark. I'd just swap it out for another.
If it somehow SHORTED... I'd think you see/smell more issues. (don't remember the V+ limit on the caps it feeds)
I don't think it would take down your tranny.
Good luck.

[tojpeters]

transformers really stink up the place when they fry. probably fine, but you could bring it up to power with a variac if you are suspicious.

[Chris Keyman]

The tube is shorted. The tube tester verifies this.
Chris

[jkrusel]

Hi,
My 122 freaked out and went dead. Upon testing the tubes I discovered the OC3 voltage regulator was shorted out and useless. Can this thing going mad take out any other components like TRANSFORMERS etc? Should I just replace the tube and see if it works? BTW how can you test a transformer without turning the thing on? I used my fluke meter and I can tell you the capacitors seem ok. There are also no open resistors.
Chris

BEFORE you turn it back on, check the diodes D1, D2, D3 and D4 in the power supply to make sure none of them are shorted. Use an ohmmeter and check both directions, readings should be different. If it is close to 0 ohms in BOTH directions it is shorted. If one or more are shorted you should test the power transformer also - hopefully the secondary has not opened up from the short.

If one or more diodes are shorted it's a good practice to replace ALL four of them with the same type.

Also check R17 for open or incorrect value.

[Chris Keyman]

All diodes are testing normal. 0 in one direction .5 in the other. Of course this depends on which way the bands are facing. 2 go one way, 2 go the other. If one was shorted, how do you test the transformer?

[jkrusel]

All diodes are testing normal. 0 in one direction .5 in the other. Of course this depends on which way the bands are facing. 2 go one way, 2 go the other. If one was shorted, how do you test the transformer?

I guess I'm a little concerned about your numbers. If you read 0 ohms one way and only .5 ohm the other way, that looks like a shorted diode to me. Is there something after the .5 like .5K or .5 M? That would be much more typical of a good diode.

The transformer secondary would read as open with an ohmmeter if the winding was open. A good winding would read several hundred ohms, can't tell for sure exactly how much. Readings taken with the transformer secondary disconnected from the rest of the circuit.

[Chris Keyman]

OK, I turned the amp on with a preamp pedal for a 122. The amp works (yeah) but there is no motor control at all. That is to say the motors don't spin no matter what and at any speed. If the relay got taken out could this happen? I always thought a bad relay left you on one speed only.

[jkrusel]

Chris:

I must be getting dense in my old age but I do not understand what you are saying here:

OK, I turned the amp on with a preamp pedal for a 122.

Did you replace the voltage regulator tube? What about the diodes?

If the relay is physically removed you won't get either slow or fast.

[Chris Keyman]

Hi again,
The diodes are fine. The Oc3 tube is replaced with an NOS RCA unit. There are some strange things going on with this 6-pin amphenol on the front end. I think I should replace it. If you don't hold it with pressure on it the amp shuts off or makes itermittant noises. BTW a pedal preamp is a little box designed to plug a mic or guitar into a Leslie and also supply power and switching to it. I don't understand why I'm not getting any AC to the motors. The relay in here is solid state and connects directly to the AC sockets. Maybe it went bad.
Chris