Need help with Mainline build [resolved]

[Larpy]

Finished my kit yesterday and LEDs on the B side of the chassis C side C4S board are not lighting up.

Here are the measurements I got:

306v from both 275v DC taps on the PS board.

On the C side C4S board, 303v at left side of 3W 100K resistor. 0v on the right side of the 2W 100K resistor (on A side C4S board [where all LEDS light up], I get 216v on the left side of the 2W 100K resistor).

Ov on either side of the B side 37.4 resistor (305v and 272v across the A side 37.4 resistor).

OA tap on the A side C4S board measures 220v; OB tap on the A side measures 143v. 

OA tap on the C side C4S board measures 0v; OB tap on the C side C4S board measures 1.02v

On the regulator board, Kreg measures 11.8 on the A side and 2.7 on the B side.  On the regulator board, A side +reg measures 220v; on the B side it measures 0v.

I swapped tubes and got the same results.  I also replaced the 12AU7 with another one I have.  No difference.

This morning I desoldered and rebuilt the A side of the regulator board, the B tube socket (and the relevant connections on the C tube socket), and the C side C4S board.  Inspected all solder connections with a magnifying glass and checked for continuity.

Fired up the amp and there's no change.  I'm stumped.

Here are photos:

http://imgur.com/CQ2c0wU
http://imgur.com/6tXGD0a
http://imgur.com/8tRqPAa

Thanks for any help you can provide.

Larry M.

[Larpy]

I'll repost the photos.

[Paul Birkeland]

306v from both 275v DC taps on the PS board.

That's not necessarily the end of the world.  Out of curiosity, what voltage do you get on the other side of the 270 Ohm resistor on that PC board?

OA tap on the A side C4S board measures 220v; OB tap on the A side measures 143v. 

That's pretty textbook, looks like a good channel there!

OA tap on the C side C4S board measures 0v; OB tap on the C side C4S board measures 1.02v

That's not quite possible.  OA feeds the C4S on the B side, but they are both at about 0V.

Kreg measures  2.7 on the B side.

Since your voltages are moving up in a way that doesn't make a lot of sense, my best guess at this point would be a bad solder joint at a ground connection.

Here are photos:

http://imgur.com/CQ2c0wU
http://imgur.com/6tXGD0a
http://imgur.com/8tRqPAa

Those show up as about 1" x 1"  photos.  Can you post the images here in a reply to this thread?

[Larpy]

Here are more suitably-sized photos:

[Larpy]

That's not necessarily the end of the world.  Out of curiosity, what voltage do you get on the other side of the 270 Ohm resistor on that PC board?

I assume you mean the big 5W 270 resistor?  It measures 314v on the other side.

That's not quite possible.  OA feeds the C4S on the B side, but they are both at about 0V.

I just rechecked and got the same results.

Since your voltages are moving up in a way that doesn't make a lot of sense, my best guess at this point would be a bad solder joint at a ground connection.

I'll check all the ground connections. 

Thanks for your help.

[Paul Birkeland]

You have missed a solder joint on the large high current C4S board in your photos.

-PB

[Larpy]

That was it!  How did I miss that?  I went over that board with a magnifying glass.

Thank you, thank you, PB.  After spending close to 4 hours last night and this afternoon troubleshooting, I was about to tear out my hair!

Everything measures correctly now and I've got the tubes biased.  Time to play some music.

[Paul Birkeland]

That was it!  How did I miss that?  I went over that board with a magnifying glass.

Thank you, thank you, PB.  After spending close to 4 hours last night and this afternoon troubleshooting, I was about to tear out my hair!

I'm glad you got it sorted.  A second set of eyes can be very helpful.  Back in ye old days before digital photography and image hosting, we used to recommend having a spouse check over one's work with pretty good success. 

[Larpy]

Follow-up:  amp is working just fine, but I noticed that the two LEDs on the B side of the C4S board still don't light up.  However, voltages are correct and I don't hear anything amiss in the left channel.

Should I be concerned?

[Paul Birkeland]

You may need the lights off to see them glowing.  The B side LED's will not illuminate nearly as brightly as the A side.

-PB