Left Channel Died

Kevin · 2973

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Offline Kevin

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on: August 19, 2019, 02:34:40 PM
My left channel just randomly died. Switching the tubes didn't help.

I have the C4S installed, and all the LEDs turn on.

Resistance test checks out, but for voltage, 16 is measuring 4.98v.



Offline Paul Birkeland

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Reply #1 on: August 20, 2019, 04:42:54 AM
What voltage do you get at pin 9 on the 12 pin socket on that side?

I suspect you either have an issue with the C4S board, the insulation on the connection to tube socket pin 11, or maybe a coupling cap issue.

Posting some photos of the area could be helpful too.

Paul "PB" Birkeland

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Offline Kevin

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Reply #2 on: August 20, 2019, 12:52:14 PM
I attached some pictures of the area.

At pin 9, I'm getting 1.25v.
At pin 12, I'm getting -3.05v

Thanks!


Deke609

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Reply #3 on: August 20, 2019, 01:01:08 PM
Kevin - you've probably already ruled out the problem stemming from somewhere upstream in your audio chain - but just in case you haven't: you could switch the left and right rca cables at the amp inputs (but not at the source outputs) and see if the dead channel switches sides.


cheers, Derek


Deke609

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Reply #4 on: August 20, 2019, 01:18:21 PM
Oops. Apologies - I missed the part about your voltage being off.


Offline Kevin

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Reply #5 on: August 20, 2019, 01:50:48 PM
Thank you for the input!

I was actually thinking of investigating something in my system... My DAC goes into an RCA switch that I use to switch between multiple outputs including my speaker amp and my Mainline.

I hooked up an Emotiva amp I had laying around, and for some reason, there was a lot of static in the left channel. The system played fine for a little while but eventually tripped a fault somewhere. Now, it would only play for a few seconds before tripping a fault.

My Mainline plays flawlessly though through the RCA switch. No static or any noise... But I still can't help but wonder if something in the signal path screwing with the left channel...


Deke609

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Reply #6 on: August 20, 2019, 02:16:15 PM
Maybe there's something to this. I would definitely try plugging the left output into the right input of your S.E.X. amp, and vice versa. If the problem shifts to the other channel, it's definitely an upstream issue.


Edit: and/or try plugging the S.E.X. into the switch outputs you're presently using for the Mainline. Maybe it's a loose connection in the rca switchbox?


I don't have a S.E.X. amp, so I have no idea whether your posted voltage variance is a cause for concern.


cheers and good luck, Derek
« Last Edit: August 20, 2019, 02:18:55 PM by Deke609 »


Offline Paul Birkeland

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Reply #7 on: August 20, 2019, 04:44:20 PM
16L and 18L look like they could use more heat/solder.

Paul "PB" Birkeland

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Offline Kevin

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Reply #8 on: August 20, 2019, 05:08:15 PM
I added more solder and heat. At first, 16 read a steady 4.85v. I prodded around a little more, checking the other leads, and suddenly, I noticed the LEDs on the right started shining much brighter. I measured the voltage again at 16 and it started reading 301v. I turned it off ASAP.



Offline Paul Birkeland

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Reply #9 on: August 20, 2019, 05:24:30 PM
Yeah, that sounds like loose connections.

Paul "PB" Birkeland

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Offline Kevin

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Reply #10 on: August 21, 2019, 04:04:21 PM
I just heated and added solder to all the joints from leads 15 to 28, all the pins on the affected tube socket, and all the leads on the bottom of the C4S board. No luck. LEDs on right still super bright and lead 16 reading 301v.


Offline Paul Birkeland

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Reply #11 on: August 21, 2019, 04:10:04 PM
16 reading 301V is a whole lot better than ~5V.  When IA and OA on a C4S measure about the same, I recommend reflowing the solder joints on the MJE5731A, especially the middle leg!

Paul "PB" Birkeland

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Offline Kevin

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Reply #12 on: August 22, 2019, 01:34:55 PM
I reflowed all the joints. I tested the voltage for all legs (the actual component legs, not solder joints) on the MJE5731As and the components' legs they're attached to (ie left leg to LED, middle leg to OA/OB, and right leg to transistor) and the voltages correspond, so I think the joints are solid. The measurements I got are listed below, if they might be of some helpn

OA = 70.6
IA = 368

OB = 299
IB = 315

The 3 pins on the A (left) MJE5731A measure (from left to right), 364v, 70.6v, and 365v, respectively.

The 3 pins on the B (right) MJE5731A measure (from left to right), 311v, 298v, and 299v, respectively.


Offline Paul Birkeland

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Reply #13 on: August 22, 2019, 02:28:21 PM
How's the voltage at pin 10 of that 12 pin socket? 

Now that the plate voltage on the driver has popped up, I would also do another tube swap.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Kevin

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Reply #14 on: August 22, 2019, 03:06:14 PM
Before tube swap:
10 = 0v
12 = -3.05v

After tube swap:
10 = 0
12 = -3.05

OA = 68.4v
IA = 367v

OB = 302v
IB = 318v

The 3 pins on the A (left) MJE5731A measure (from left to right), 364v, 68.4v, and 365v, respectively.

The 3 pins on the B (right) MJE5731A measure (from left to right), 314v, 301v, and 302v, respectively.


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