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

[PassionForSound]

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

 

[PassionForSound]

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.

 

[PassionForSound]

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!?

 

[mcandmar]

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.

 

[Doc B]

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.

 

[PassionForSound]

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

 

[Paul Birkeland]

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

 

[PassionForSound]

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.

 

[PassionForSound]

Some images.


WP_20131208_20_36_08_Pro by Lachfen, on Flickr


WP_20131208_20_36_14_Pro by Lachfen, on Flickr


WP_20131208_20_36_21_Pro by Lachfen, on Flickr


WP_20131208_20_36_34_Pro by Lachfen, on Flickr

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


WP_20131208_20_36_45_Pro by Lachfen, on Flickr

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


WP_20131208_20_36_56_Pro by Lachfen, on Flickr


WP_20131208_20_37_04_Pro by Lachfen, on Flickr

A side C4S:


WP_20131208_20_37_15_Pro by Lachfen, on Flickr


WP_20131208_20_37_33_Pro by Lachfen, on Flickr

B side C4S


WP_20131208_20_37_21_Pro by Lachfen, on Flickr


WP_20131208_20_37_26_Pro by Lachfen, on Flickr


WP_20131208_20_37_38_Pro by Lachfen, on Flickr


WP_20131208_20_37_47_Pro by Lachfen, on Flickr

 

[Paul Birkeland]

Did you follow the instruction in red/bold on page 28?

 

[PassionForSound]

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...

 

[Paul Birkeland]

Oops, that'll cause some funkiness!

 

[mcandmar]

/slightly off topic: looking at the pin outs is only half of those tubes used on each channel?  (assuming they are 12au7)

 

[PassionForSound]

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?

 

[Paul Birkeland]

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?

 

[PassionForSound]

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?

Thanks for all the help!

IB / OB is 216-218V on all pads (i.e. IB and OB pads) and on both C4S boards

I assume the jumpers are the black lead on the underside of the board? If so, yes, they are in place.

 

[Paul Birkeland]

Yeah, your 6C45's still aren't drawing any current, but at least you have them heated!

This issue points to an error on the center regulator board, in the trim pot/2N2222A wiring.  I don't have one of those PC boards in front of me to be 1000% sure that your accidental miswire of the trim pots will have no effect.

How about the OB/OA voltages on the center PC board?

 

[PassionForSound]

I'm officially a numb nuts! 

In my head, having the 2 leads under the regulator pots go through the same hole on the board was fine. In reality it was leaving a pad on the circuit board disconnected so the F or E (can't tell what it's meant to be) pad was empty and not connected to the C pad as it was meant to be. In my mind it was about connecting the trim pot leads - I didn't even think about the pads on the circuit board.

Long story short, the LEDs are now all lit and I'm ready to do the biasing adjustments...

 

[hopeful]

Congrats on the debug and your completed mainline! 

 

[PassionForSound]

Thanks Mike!