B side LEDs not lighting and Kreg V is 50% of ideal [solved]

Loquah · 4638

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Offline Loquah

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I've finished my build and all impedance checks were good, but the B side LEDs on both C4S boards aren't lighting. I'm also getting half the expected voltage on both KReg checks (getting around 4V).

I've done a quick check for missed solder joints, etc. and am about to go back and retrace my steps in the manual, but any help would be appreciated if these symptoms point to a specific error.

PS tried an alternate 12AU7 tube in case that was the culprit, but it wasn't
« Last Edit: December 08, 2013, 12:32:03 PM by Caucasian Blackplate »

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Offline Loquah

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Reply #1 on: December 07, 2013, 09:54:41 PM
Update. All components and wiring on C4S & Bias boards appear correct and soldered.

I made an error in my previous post though. The B LEDs don't light up on the "A" OT side of the chassis while the A LEDs don't light up on the "C" OT side of the chassis.

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Offline Loquah

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Reply #2 on: December 07, 2013, 10:21:18 PM
Continued troubleshooting...

The A side tube doesn't light, but the heater circuit is supplying 6.3V and the earth from the A side tube heater is good.

After unscrewing the A side C4S board and remounting it IS the B side LEDs which aren't lighting. I can't explain what changed!?

Tried changing the tubes over with no luck - there is a problem with my circuit I think, but I can't work out why the tubes won't glow if there's a definite 6.3V across the terminals!?


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Offline mcandmar

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Reply #3 on: December 08, 2013, 05:00:16 AM
I'm going to preempt the BH guys and say post up your voltage test results, will help them narrow down where is the issue is.

M.McCandless


Offline Doc B.

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Reply #4 on: December 08, 2013, 05:36:05 AM
Yes, give us any voltages that are off from the values in the manual. If you had an LED string come to life when it was moved there was most likely an interemittent connection to the board or at the other end of a lead coming off the board, or at the tube socket - either a tube pin or a solder connection on the pin.

As usual check that LEDs that don't light are not installed backwards and also check that the transistors are oriented properly.

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Offline Loquah

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Reply #5 on: December 08, 2013, 09:02:11 AM
All voltages are on the money except for the KReg readings which are around 4V.

All resistors are correct on the boards as are the transistors.

I've re-checked the solder joints around the tube sockets and resoldered one which had excess solder, but still not luck.

Any further thoughts?

PS photos to follow

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Offline Paul Birkeland

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Reply #6 on: December 08, 2013, 09:12:24 AM
The 4V at Kreg isn't a problem, the regulator will still operate.  IIRC, there was an error in the manual and it looks like we haven't corrected the Kreg voltages to be a large enough range.

A b-side C4S may or may not be tube related.  If a 6C45 doesn't glow, and whichever 6C45 you put in the same socket won't glow, then you have an issue at that socket.  If the 6C45 isn't glowing, the B side LED's over it won't light up, and OB is going to be pretty high. 

-PB

Paul "PB" Birkeland

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Offline Loquah

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Reply #7 on: December 08, 2013, 09:20:57 AM
I have one side tube glowing, but neither side's B LEDs glowing!?

The manual states a range of around 8-10V (or maybe 12V) I think (I'm away from the manual at the moment)

Would solder touching the small resistors between the terminals and centre of the tube sockets cause problems? It's not shorting with anything, but has touched the body of the resistor.
« Last Edit: December 08, 2013, 09:30:53 AM by Loquah (Passion for Sound) »

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Offline Loquah

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Reply #8 on: December 08, 2013, 09:29:27 AM
Some images.

(http://farm8.staticflickr.com/7355/11276093924_30c9a98b62.jpg)
WP_20131208_20_36_08_Pro by Lachfen, on Flickr

(http://farm3.staticflickr.com/2885/11276067186_568d935387.jpg)
WP_20131208_20_36_14_Pro by Lachfen, on Flickr

(http://farm3.staticflickr.com/2823/11276073526_5ea99298d5.jpg)
WP_20131208_20_36_21_Pro by Lachfen, on Flickr

(http://farm3.staticflickr.com/2864/11276078266_ca88a5ae2f.jpg)
WP_20131208_20_36_34_Pro by Lachfen, on Flickr

Pretty sure this is the A side inboard terminal strip (below):

(http://farm4.staticflickr.com/3794/11276084506_700f737339.jpg)
WP_20131208_20_36_45_Pro by Lachfen, on Flickr

Pretty sure this is the B side inboard terminal strip (below):

(http://farm3.staticflickr.com/2814/11276089936_139e7dc1c0.jpg)
WP_20131208_20_36_56_Pro by Lachfen, on Flickr

(http://farm6.staticflickr.com/5535/11276055645_f50fc0aed8.jpg)
WP_20131208_20_37_04_Pro by Lachfen, on Flickr

A side C4S:

(http://farm4.staticflickr.com/3775/11276061985_0e1252837b.jpg)
WP_20131208_20_37_15_Pro by Lachfen, on Flickr

(http://farm3.staticflickr.com/2807/11276151124_a3603f4510.jpg)
WP_20131208_20_37_33_Pro by Lachfen, on Flickr

B side C4S

(http://farm6.staticflickr.com/5543/11276106596_002e115810.jpg)
WP_20131208_20_37_21_Pro by Lachfen, on Flickr

(http://farm4.staticflickr.com/3795/11276145714_00ae06245e.jpg)
WP_20131208_20_37_26_Pro by Lachfen, on Flickr

(http://farm4.staticflickr.com/3666/11276196853_071279397f.jpg)
WP_20131208_20_37_38_Pro by Lachfen, on Flickr

(http://farm8.staticflickr.com/7366/11276130316_73e9bc5c1a.jpg)
WP_20131208_20_37_47_Pro by Lachfen, on Flickr

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Offline Paul Birkeland

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Reply #9 on: December 08, 2013, 09:32:35 AM
Did you follow the instruction in red/bold on page 28?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Loquah

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Reply #10 on: December 08, 2013, 09:50:40 AM
Yes, although I misread the instructions and put both leads through the centre hole. Same outcome though, just not as neat.

I think I found the issue though. My numbering of the A socket went a bit wonky due to small space and larger marker  ;) I have wired the A4 / A5 connections to A3 / A4!!

Fixing now and will report back...

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Offline Paul Birkeland

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Reply #11 on: December 08, 2013, 10:05:07 AM
Oops, that'll cause some funkiness!

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline mcandmar

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Reply #12 on: December 08, 2013, 10:06:53 AM
/slightly off topic: looking at the pin outs is only half of those tubes used on each channel?   (assuming they are 12au7)

M.McCandless


Offline Loquah

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Reply #13 on: December 08, 2013, 10:08:07 AM
Fixed the A4/A5 wiring and I now have glow on both tubes - hooray!

But still no "B" LEDs on either side - booo!

I'm not very good at tracing circuits. Where does the power come from that lights the B LEDs?

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Offline Paul Birkeland

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Reply #14 on: December 08, 2013, 10:10:40 AM
What's your IB/OB voltage on both of the big C4S boards? 

Can you triple check that the bA/bB jumpers are in place?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man