Right channel suddenly out [resolved]

[dyrstr8s]

So after working just great for weeks, suddenly at start up no right channel output.
I poked around underneath with a chopstick with the amp playing but never got anything.
I ran through all the voltage and resistance checks from the assembly manual and all look great.
I didn't think the center solder connection on the rca input connector looked too great, so I removed and resolved. The connector itself seems "wiggly" but the attaching nuts are all tight.
It seems like it is the signal path, either input or output? Any suggestions how to narrow it down would be appreciated.

 

[Paul Birkeland]

Can you let us know which meter you have? If your meter is able to resolve very low AC voltages, we can provide some instructions on injecting a 60Hz signal into your amp, then you can follow it with your meter and see where it stops.

The most common problems for an issue like this are output transformer/binding post wiring issues, or a shorted RCA jack.

-PB

 

[dyrstr8s]

I have a Klein mm325.

 

[Paul Birkeland]

The Klein won't do the job (and they are kinda irritating to use).

https://www.amazon.com/AstroAI-Mult...151&sprefix=digital+mete,aps,194&sr=8-10&th=1

That one has an AC scale that goes down to 6V AC with good resolution.

 

[Jameson]

I have and love that one

 

[dyrstr8s]

Ordered!

 

[Paul Birkeland]

While you wait for that to arrive, you'll need a device that can play a 60Hz tone into the Kaiju. I accomplish this with an old phone running a signal generator app using an 1/8" to RCA cable out of the headphone jack.

 

[dyrstr8s]

I received the new mm this morning and found a 60hz test tone to play on Qobuz, so ready to roll.

 

[Paul Birkeland]

The first thing to do is to turn the volume up all the way on your source and use the meter to measure the AC voltage available at the RCA jacks when they aren't plugged into the Kaiju. Typically I would expect to see something around 0.3V to 3V. To measure this, it's just one probe on the center pin of one RCA cable and one pin on the outside shell, then the AC voltage should pop up on your meter.

 

[dyrstr8s]

409 mv, .4v?

 

[Paul Birkeland]

Now plug the RCA cables into the amp, turn the trim pots all the way up, and test these voltages again on the center lugs of each trim pot (you can use the chassis plate as your ground reference). The amp doesn't need to be powered up for this. If you see the same voltages, you can move on.

Now turn on the amp and let things warm up. With the signal playing, check pin 3 of each 300B socket, you should see something like 10V or so AC there. If you see the same voltages, then you can move on.

Now measure the AC voltage between pins 5 and 10 on each output transformer. I'd expect something around 35V or so on these tests. If you have an issue with the wiring around the output transformers, you may notice a substantial imbalance here rather than a 0V reading, so this is also useful information.

 

[dyrstr8s]

OK found a longer 60hz track on qobuz, through my preamp I boosted to ~300 mv at the rca inputs. Then measured ~8 v at the c3 socket pin and ~ 45 mv at b3.

 

[Paul Birkeland]

8V is what I would expect.

45mV at B3 means you have nothing coming out of the driver stage.

Can you double check the AC voltage level at the center lug of the trim pot on that side of your amp?

I'd also post the OB and KregA voltage on the C4S board on that side.

Also (with the amp off) double check that the resistance between B3 and ground shows 249K.

-PB

 

[dyrstr8s]

Center lug of the trim pot reads 64mv
OB reads 0
Kreg on the A side reads 65mv
Resistance at B3 is 249kohm
Thanks Paul!

 

[Paul Birkeland]

Sorry, the center lug should be an AC voltage. If you have 64mV AC, then the signal isn't getting into the pot, and I'd be looking for solder shorting across the RCA jack.

OB/KRegA should be in DC volts.

Good to see the 249K where it's supposed to be.

 

[dyrstr8s]

Tried it again.
~250v ac at the rca plug.
~250v ac at the center lug on the pot
~177v dc at OB
~3.65v dc at Kreg
I think I need to resolder OB, moving the probe around on it with some pressure it popped through the speaker and the readings fluctuates wildly. With a little pressure I got tone through the right speaker and a consistent 177v. There's not a full scallop of solder at the joint and it looks dark like a cold joint.
Does that sound right?

 

[dyrstr8s]

Rca plug and center lug were mv not v.
Does 177v at OB sound right? I was encouraged to hear the right channel through the speakers.

 

[Paul Birkeland]

177V DC at OB is OK. You could get that closer to the target by following the basing procedures.

Pushing on OB will move a lot more than OB, so I wouldn't necessarily focus your soldering efforts there. I would continue to poke around and see if you can see anything that moves/pops extremely regularly when you probe it. Either way, it sounds like a solder joint is causing your issue (or crowding on the pins of the 9 pin socket).

-PB

 

[dyrstr8s]

Resoldering OB seems to have done it. I touched a bit more while i was at it.
Now that it's working well, I installed my dc filament upgrade and replaced the binding posts with some really nice Cardas posts.
Sounds amazing!
Thanks for guiding me through the diagnosis Paul!