Right channel noisy. Help troubleshooting

[denti alligator]

New tubes in. Voltages look to be normal now. I guess it was a bad tube after all. Maybe even explains how that resistor got shot?

 

[denti alligator]

ONe major problem solved. Next one predates this and I thought it was related, but it persists:

Intermittent scratchiness in right channel

Switching tubes does not change this
Selecting different input does not change this
Balance control does not eliminate (so even if I move the balance all the way to the left channel, I still hear the scratchiness in the right channel)
Hum pot doesn’t change it
Volume doesn’t affect it.

I tried reflowing some of the pins of the 9-pin socket and some terminals on the right side. Nothing yet.

I assume this is a loose wire or bad solder joint. Any suggestions for which terminals I should attend to first?

Thanks!

 

[Paul Birkeland]

Hook up a really cheap pair of speakers to the Stereomour while it's running and use a wooden chopstick to poke around in the circuit.  When you poke at the problematic connection, you should get a nice pop through one or both speakers.

 

[denti alligator]

Hook up a really cheap pair of speakers to the Stereomour while it's running and use a wooden chopstick to poke around in the circuit.  When you poke at the problematic connection, you should get a nice pop through one or both speakers.

I tried all over the place, but nothing. Couldn’t even determine a connection between my poking and the scratchiness. How hard should I be doing this? I was poking on every terminal and pin.

It’s quiet now. It can be totally quiet for several minutes and then start up again.

 

[Paul Birkeland]

Are you 100% sure this isn't noise from a wireless device getting into your Stereomour?  This kind of noise sounds more like a Morse Code pulse with somewhat irregular periodicity.

 

[denti alligator]

No. That might be it. Let me move things about a bit and see what happens.

 

[denti alligator]

I unplugged all other transmitting devices nearby. No difference.

I moved the amp to the other side of the house, into a room where there are no electronic devices at all. Same problem. Right channel only.

 

[Thermioniclife]

Try cleaning the tube sockets and pins?

 

[denti alligator]

Try cleaning the tube sockets and pins?

Busting out the Deoxit! Though Paul is right that the intermittent nature of this points to some external interference. But a) why only the right channel and b) why no change in other parts of house?

 

[denti alligator]

Throwing up my hands!

Still scratchy. Pretty quiet. Maybe I have to learn to live with it?

 

[denti alligator]

Is it possible it’s not a connection but something in the transformer?

 

[Paul Birkeland]

No, it's not a transformer or a part that's doing that. This issue sounds a lot like a contact problem like a cold/loose solder joint or tube pin corrosion, though you ruled that out with some new tubes. 

Did your DC voltage issues disappear completely?

 

[denti alligator]

Yes. The only discrepancy is the terminals that are supposed to read 58 are 51.6 on the left and 56.6 on the right.

 

[denti alligator]

I’m continuing to prod the circuits with a chopstick. Nothing. I’m trying every terminal, every wire, every socket, every resistor and capacitor, every connection on the PC boards. Nothing.

Last time I turned it on the scratchiness started before the LEDs lit up. Not sure if that tells you anything.

However, for the last 2-3 minutes it has been quiet. ??

 

[denti alligator]

It’s back. Have we exhausted troubleshooting options?

Again:

- volume is turned all the way down
- balance doesn’t change the scratchiness
- it’s very intermittent (sometimes stops for minutes at a time)
- but I turned off my router, all close by electronics and shut off phones (no difference)
- prodded every single terminal and connection while on with no increases in sound.

 

[Thermioniclife]

You said you replaced the tubes, did you replace all tubes or just the 2a3's?
My money is still on the 12at7 on the offending side. a thorough cleaning / scraping of the pins and socket may help.

 

[Paul Birkeland]

Last time I turned it on the scratchiness started before the LEDs lit up. Not sure if that tells you anything.

That tells me it's most likely that your issue is in the power supply and/or output stage, so 4 pin sockets and power supply wiring, not the C4S boards and 9 pin sockets.

 

[denti alligator]

That tells me it's most likely that your issue is in the power supply and/or output stage, so 4 pin sockets and power supply wiring, not the C4S boards and 9 pin sockets.

OK, I’ll go and reflow those. Which are the main terminals for the power supply on the right channel?

I replaced the 12AT7s. The 2a3s are not an issue I don’t think. At the least, when I switch them the scratchiness stays in the right channel.

 

[Thermioniclife]

The SM2 uses a pseudo dual power supply, check/reflow the 130 ohm resistors and the 100uf caps on the offending side and also the connections where it connects to B+

 

[denti alligator]

I reflowed and added a little solder to the right side 4-pins and terminals connected to it and to the terminals where the 100uF caps are and to the tabs on the chokes.

Turned it on: scratchy.