Problem with Integration Upgrade + Reduction-- first part of build [resolved]

[BJK]

Okay... so I built/installed the first board. Initially the voltage checks didn't look right, so I took out the tubes, redid some of the gnarlier solder joints, and then it all checked out well.

All the LEDS light up on the new board, voltages look right. But one of the LEDs on the right channel by the tubes isn't lighting anymore. Not that I touched any of those joints. I kind of wiggled the pins, resoldered a joint or two... and it still won't light. Pictures below. Any ideas?

[Paul Birkeland]

This is most likely caused by an underlying issue in the original build.

I would reheat all of the solder joints on the two 8 pin terminal strips that flank that socket.

You can also try measuring the DC voltage at that pins 8 and 6 on that socket.  My guess is that you will have 0V at pin 8 and either 0V or very high voltage at pin 6.  It also wouldn't hurt to be sure that you have 0V at pin 7, just be careful making that measurement.

[BJK]

okay-- re-did all the joints on the two strips... Pin 8 and 7 are both 0. Pin 6 is about 32 volts.

Still not lighting on that LED.

Any thoughts?

[Paul Birkeland]

With the Reduction powered off, what is the DC resistance between pin 8 on that socket and ground?

When an LED fails, it fails open and you get a voltage on that socket that's higher than 1.5V.  If the connection to A7 is bad, then you'd see something other than 0V there, which is also a problem.  In your case, it appears that you have pin 8 grounded.  It's hard to say from the photos, but is anything touching between pin 8 and pin 9?  That would cause this exact problem.

[BJK]

A couple of things... it's the 'B' channel, as per the wiring instructions. Not sure if that matters.

Took measurements with power off, tubes in.

Pin 8 starts with some resistence, and then flys out to infinity. (Probably because maybe a cap is charging at first?). From what I can tell there's nothing touching between 8 and 9 besides the LED between them. So I think 8 is closed?

Pin 9 is 0 ohms, which I expect because it's wired straight to ground.

[BJK]

Just bumping in case anyone has some input... 

Caucasian Blackplate, any more insight based on what I measured?

[BJK]

Gah--I fixed it. Soooo... it was a bad solder joint...probably? I promise, promise I went back and redid each of the joints.

I spent the afternoon fiddling with making some cables with a buddy, and then, I kind of had a sense of determination to figure this out. (Not to mention my crappy backup pre-amp was so noisy and driving me nuts)...

I rechecked all the resistances... and noticed with pin 8, on that socket, I would get different results depending on where I touched the pin. (Sometimes I'd get resistance, and then the LED would light up slightly and it'd hit infinity.). So I resoldered it again, probably for the 3 or 4th time. But maybe I was more careful, or maybe just who knows... And then it seemed to be consistent with the other channel. SO everythign checked out... I plugged it in.. and.... ahh.

I suspect this problem may have been going on since before I even started the upgrade. (As per comments above). I wonder if this is consistent with a balance issue I noticed (Which I thought had to do with my amp, I had to cheat it all the way over to one side to make it sound correctly balanced.) This seems to no longer be an issue. Is that consistent with what may have been going on? Am I just imagining things?

Okay... on with the rest of the upgrade. Ahhh.......

[Doc B.]

You have perfectly described a cold solder joint that you eventually got hot enough for the solder flow properly. A cold joint often has a layer of flux under the solder that keeps the solder from creating good contact between the wire and the terminal. It takes even heating of both of them to get the solder to flow well over their surfaces and displace the flux.

[BJK]

Thanks!

Quick follow up question. How much heat can those LEDs take. I'm getting some intermittent static on that channel. (That's both cleared up and/or exacerbated by tapping). I suspect that joint still needs some help.

How hot can I make it? (Which is to say, how long is too long to leave that iron on the joint)? IF it helps answer the question I have a hakko digital soldering station set to 650F.

[Paul Birkeland]

I solder with the temperature all the way up.  When you overheat the LED, it will no longer glow.  Generally speaking, the flat leads coming out of the LED body isn't that great at conducting heat, so it's not a huge concern.