Voltage check question. 10 and 44-45 [resolved]

[canonken]

Resistance check good, 4 LEDs are illuminated, tube heaters visible after a few seconds.

I found this thread and have the same issue with 80V showing at 44 and 45.  I will let it sit running for a bit and check later.  Bottlehead crew, can you validate if I need to wait for these values to go to zero before even thinking about connecting anything?
https://forum.bottlehead.com/index.php?topic=13131.0

I have have 80V on 10.  I looked and do not see an immediate issue, wanted to see if this jumps out as something specific.  I do notice 2, which reads 80V is connected to 10 via a capacitor...so is that where I am getting this reading?

Thanks!

 

[Doc B]

80V at 10 is no bueno. That implies that the 475K resistor between 10 and 11 is not properly grounded. Try reflowing 11L and check again.

 

[canonken]

Thanks for the quick reply.

I tried to reflow 11L from both sides.  I then checked continuity all around 11L and 11L, including right on the lead to the capacitor (see picture) and I got a beep for continuity.

I can certainly keep trying to heat things (worry about damage if I do too much, you tell me otherwise!), but theoretically if I damaged the resistor, would that cause my issue?

Ken

 

[canonken]

If it helps:

I get a 475k ohm reading on 22/23, no issue.  Instantly snaps to it.

I do the same on 10/11 and sometimes it reads 4M ohms or 40k ohms depending on where I read it from, and the reading drifts.

 

[Paul Birkeland]

Maybe you could post some pics of your build in that area.  Usually what you are experiencing is from a loose solder joint.

 

[canonken]

Sure here.  This is after I reflowed, so it got a little messy.  Some of the texture is from the point of the test leads scratching the solder.  I soldered both sides on this to see if it helped, before it was just the front.

I generally cut the leads long, solder, then trim.

 

[Paul Birkeland]

The solder joint of that resistor where the 0.47uF cap connects looks a little cold.

 

[canonken]

I soldered it from the other side, and have been scratching it with the test leads.  It had a full wrap of the wire around the lug before I soldered.  I do have continuity between the cap lead and lug.  I shook it hard and it does not move.

 

[Paul Birkeland]

This one.

 

[canonken]

It was OK, I 'unfixed it' reheating the top, and have now refixed it.

While I will trust the pros here, I feel like I have reheated the joints a few times and still getting that reading.

Appreciate the help.

 

[Paul Birkeland]

Can you completely remove that resistor and measure it with your meter?

 

[canonken]

It is out, it reads 475k.  Hmmmmmmm........

I really cranked away on those joints and not sure why it didn't work.

Am I safe to do a temporary reassembly with the resistor tacked across 10U and 11U to see if that works?

 

[Paul Birkeland]

I would just put it back down there and really reflow those joints.

 

[canonken]

Unfortunately, the resistor is now broken, one lead has come off.  Yikes, and this is the worst possible location for trying to get the new one in.  Honestly not sure I can get it back in from the tube side and might try it from the other side.

I'll e-mail and order a new one. 

Thanks,

Ken

 

[canonken]

Also, even though I need a new one - is there ANY other possible cause (the big cap between 2 and 10) to rule out - or is it only possible the issue is at the 475K cap between 10 and 11?

 

[Paul Birkeland]

You can pull the cap out of the Reduction completely with the new resistor installed to see if that changes anything.

If you hit the cap and burn it enough with the soldering iron, I'm sure it could be damaged, but this is pretty rare.

 

[canonken]

New resistor on the way.

Before I solder it back in, is there ANYTHING else that I should check or could cause this?

Thanks,

Ken

 

[canonken]

AAAGGGGHHHH!!!

Put in the new resistor and still reading 80 volts on 10.

Is there anything else (the chain of components between 10 and 15) that could cause this issue?  As you know, some of these parts are hidden when the 4 caps are installed.  If it is electronically impossible for it to NOT be something else, that would help.

I'm not sure what else to try.  I don't know how I could assemble the rest of the kit correctly, but continue to fail at reflowing 10 and 11, then removing, replacing the resistor.  I am not saying I am skilled, but I feel redid the connections enough it would work from dumb luck.

Is there something I can do to rule out the .47uF capacitor as the culprit?

Thanks!

 

[Paul Birkeland]

Remove the 0.47uF cap from that side of the amp and recheck the voltage.

 

[canonken]

Thanks for the reply.

Won't that mean 0V on 10 by default - as the only way I am getting 80V to 10 is via the 80V on 2?  I get 73V on 13-15 (not 80V).

Or are you asking to remove one of the two leads from the cap (I can lift it out of the way, make sure I don't touch it) - and recheck voltage on 1-16 (the entire affected side)?