Help with earthquake pa-2050 low volume

[Cmac423]

Amp is a 2ch, channel 1 has very low output almost none. Ch 2 works just fine, works just fine when when its bridged. But seems like channel 1 is getting the sound from ch 2, because sound only comes out if rca is plugged in side 2. Not 1. I dont get anything at all out of either channel when I plug in ch 1 rca. Kinda confusing I know, but that's what's going on and cant figure out what may be up. Any input?

 

[Bills amps]

check for broke solder joints around the rca's

 

[Perry Babin]

With signal and a speaker connected to the dead channel, does operating any of the controls on the front panel ever cause any noise or allow the channel to produce audio?

Does pushing on the board (with a non-conductive probe) change anything?

Don't turn the internal pots.

 

[Cmac423]

Solder joints are fine, and no I tried switching the hp/fp/lp switch and wiggling the gain knobs. Nothing.. I have not tried pushing on the board but I will try that and see if anything happens! All the filter caps look to be good. The board is very clean

 

[Perry Babin]

What are the part numbers on Q107/Q207?

 

[Cmac423]

I'll have to check I'm not sure, soon as I get home I'll look

 

[Cmac423]

Q107 is 2N 5458 and q207 is the same.

 

[Perry Babin]

What's the DC voltage on leg 3?

Either leg 2 or leg 3 is connected to ground. For the one that is NOT connected to ground, do you have audio on both transistors?

What's the DC voltage on the power supply pins of the op-amps in the preamp section? Place the black probe on the RCA shield.

 

[Cmac423]

I think my batteries are going dead on my mm because they are reading -18.9v dc? I'll replace the batteries and give it another go

 

[Cmac423]

I'm not reading any voltage on the q107 or 207. Read 18.8 from pos to neg on the legs though..

 

[Perry Babin]

On which legs?

Place the black probe on the RCA shields and measure the DC voltage at 3 points.

Terminal 4 on the op-amps?
Terminal 11 on the op-amps?
Terminal 3 on the two transistors?

 

[Cmac423]

-5.40 on leg 4, 11 reads nothing. Leg 3 on trans read nothing. But if I ground to my amp ground everything reads different. Could it be something with my rca? Because when I ground to rca shield and test my main voltage it says .932 vs what it should be, 13.4

 

[Perry Babin]

The amp has an isolated secondary. There is no connection between the primary and secondary grounds. That's why you need to measure the audio voltages with the black on the shields.

What's the resistance between the RCA shield and one of the non-bridging speaker wires?

You may be missing the negative regulated voltage or the zener used for regulation may be leaky. I'm not entirely sure how this amp is laid out. I'm guessing it's an early ZED.