Occasional popping sound - pictures and initial troubleshooting [resolved]

[Mike1590]

The issue definitely seems to be in some way related to that smaller "A" socket. When I wiggle around that tube, I am getting the popping noises. Nothing happens when I move around the larger one. In any case, I took a few more pictures... which have made me realize just how messy my install is!  pardon the melted wire insulation.

[Doc B.]

What kind of solder did you use? There is a lot of excess flux on those joints.

[Mike1590]

I used Cardas Quad Eutectic Solder with Rosin Core.

[Paul Birkeland]

Which LED goes out? What are your voltages when it goes out?

[Mike1590]

Those are good questions, Paul. I can try to replicate the issue and measure it then. How should I measure the voltage when it goes out - where should be DVM leads go?

I think the LED that briefly went out was the one attached to A3... I'll verify if I'm able to replicate the issue tomorrow.

[Paul Birkeland]

Just let me know which LED is out and what the voltages are on terminals 1-5.

[Mike1590]

10-4, I will report back tomorrow. Thanks again!

[Mike1590]

I actually had a chance to check on these tonight. Lucky (maybe the wrong word) for me, the LED was already out before I started checking voltages. The problem LED is the one soldered onto pin A3. The issue appears to be with terminal 5. Here are my voltage readings now:

1. 81.2
2. 165.9
3. 0
4. 165.6
5. 148.5

[Paul Birkeland]

Measure the voltage at A3.  If it's around 12V, the LED is damaged.  A workaround for this is to connect a wire between A3 and A8 to restore operation.

If the voltage is 0V, that means the connection at A4/A5 isn't solid and needs more attention. 

If it's something else, be sure to let us know.

[Mike1590]

It’s measuring ~.89 V - so about 0. Would that imply needing to touch up A4/A5 then?

[Paul Birkeland]

Are both halves of the 12AU7 glowing?  It is most likely that the solder joint at A4/A5 is loose.

[Mike1590]

It looks like the tube is fully illuminated, but I do have the top of the chassis upside down while I’m working on the undercarriage, so I don’t have the best view. I touched up A4/A5, but terminal 5 is still reading ~150V. Any other thoughts where this extra voltage could be coming from? I’d also be happy to take a picture of A4/A5, but I’m pretty confident in that soldering now.

[Mike1590]

Also, A3 is still measuring about 0.6V. So that would imply that the issue is still with A4/A5 based on one of your previous replies. I will provide a picture of those connections.

[Paul Birkeland]

What's the DC voltage at terminal A2?

The excess voltage is there because the tube isn't conducting.

[Mike1590]

Ah, makes sense. Here is a new photo of the connections on that socket - specifically A4/A5 shown. I will check on the voltage of A2. Side note, what is all of that orange/brown stuff? I never noticed all of it until I started working on the underside of the chassis again recently. As far as I know it isn't affecting performance at all, just looks messy/dirty & I'd like to clean some of it off if possible. Unsure if it's excess solder that's fallen off my iron while working maybe?