Final Test Failure [resolved]

[nipsy]

I just performed my final tests. Resistance test passed with flying colors.

The final voltage test failed in 4 areas. Here are the values I measured.

IA — 218
IB — 217
OA — 148.1 **
OB — 168
OC — 142.1 **
OD — 95.5
OkA — 140.9 **
OkB — 96.1
OkC — 6.1 **
OkD — 1.13

Per an earlier post, I removed the blue wires and tested voltages on the regulator board:

OA — 216
OB — 216
BREG A — 218
BREG B — 217
KREG A — 3.31
KREG B — 4.48

I’ve attached a couple of images. Let me know if another view would be helpful in diagnosing the problem.

Any thoughts on what I should inspect or measure next ?

 

[Paul Birkeland]

Can you unscrew the front C4S board and show me a shot of the wiring underneath it? (Of the C socket)

 

[nipsy]

How are these ?

 

[Paul Birkeland]

The servo on one side is forcing the EF86 to draw no current.  This could happen from a flaky solder joint (perhaps on the forward C4S board), a miswire (which I don't see), or possibly a swapped pair of resistors (the brown Dale resistors are easily mixed up).

-PB

 

[nipsy]

Hi Paul,

Thank you for your suggestions. I tested all the Dale resistors on the board and they all checked out as being correct.

I removed the CS4 board and reflowed the connections and neatened things up a bit. I touched up the solder on a couple of wire connections that looked a little on the weak side.

Resistance check was good. Voltage check gave me nearly identical results

IA — 218
IB — 218
OA — 147.9 **
OB — 165.7
OC — 142.3 **
OD — 97.6
OkA — 141.1 **
OkB — 98
OkC — 6.18 **
OkD — 1.49

What else should I inspect and test ?

Thanks again for all your help and support. I really appreciate it.

 

[Paul Birkeland]

If pins 3 and 4 touch on the EF86 socket on that side, problems can arise.  This is why the wire connections are supposed to be wrapped up and over the tube socket pins, not around the sides.  There's also an indent on the top of the socket terminal to keep the wires in place while soldering.  Still, this isn't likely to be your problem.

In the absence of anything else, trying a different 6DJ8/6922 wouldn't be a bad idea.  You have no operating voltage across one half of the circuit but that side of the 6922 is still passing operating current, so this would be the next step I would try.

 

[nipsy]

Well. Consider me stumped.

I removed the C4S board again and tidied up the C and A socket solder joints. The resistors in the sockets tested There didn't appear to be anything touching, but some wires were close.

I swapped positions of the tubes in the A and B sockets. No change.

My Decware ZKIT1 had a 6922 tube equivalent and I swapped that in and re ran the tests. Slightly different, but essentially the same.

IA — 217
IB — 216
OA — 157.1 **
OB — 169
OC — 138.8 **
OD — 95.7
OkA — 137.5 **
OkB — 95.9
OkC — 5.96 **
OkD — 1.78

Interesting side note: The 6922 that came with the Bottlehead kit had a lot more bass to it when I popped it into the ZKIT1. This place of stuckness has inadvertently opened up the world of tube rolling for me. Oh no !

I'm not sure what role the LEDs play, but the four on the shunt regulator board all glow with uniform brightness. The eight on the C4S aren't as bright. The ones next to the PN 4250A are the dimmest and the two on the IA side of the board are dimmest of all.

What's next to track down in this mystery ? Is it possible that I somehow damaged one or more of the components on the board ?

 

[Paul Birkeland]

This kind of issue is most likely to be related to solder joints and/or things touching around the sockets that shouldn't be.  If excessive heat is used to solder the LEDs on the forward C4S board, that can cause some damage, but otherwise that kind of issue is absurdly rare with the other components on that board. 

This may end up just needing to be sent in with the repair service.

 

[nipsy]

Thank you for all the time and energy you've spent with me on this. I hate to admit defeat so I think I'll give it a day or two's rest and then take another look with fresher eyes. I feel like I am so close and yet so far.

I have a few more questions with regard to strategy.

Am I correct in assuming that the problem is related to the IA side of the C4S board ? And if that's the case might I focus exclusively on that side and not the B side ?

Would it be helpful to remove and reseat any of the components on the board ? if so, which ones?

In terms of the sockets, it seems as though I would direct my attention on A and C then following the wires and connections from there, checking the joints. Seems that the right parts are in their right places and orientations.

Of course one of the biggest handicaps I have is not really knowing what I'm doing or how the parts I'm working on actually work and work together in the circuit. I feel as though I'm pretty good at following directions but I'm easily distracted.

Any other strategies or refinements you could offer would be appreciated and helpful. I hate to give up and sent it in for repair, but if I'm stuck, I'm stuck.

 

[Paul Birkeland]

The Eros circuit has two directly coupled stages and proper operation of each half depends on proper operation of the other, so everything has to be triple checked to get an issue like this resolved properly.  Still, you have basically no voltage across the 6922 on that side, but I can't see why from any of your photos.  When I have had repairs sent in with similar voltage issues, usually it ends up being a miswire.

 

[nipsy]

Thanks for that.

Tomorrow morning I'll start at page 1 of the manual and work my way through, inspecting each step as if I were performing the action described. I'll correct the things that look hinky and retest at the end of that process.

Do you think I'll need to remove and inspect the other two PCBs ? My thought is since I passed all the tests up to this one that they must be fine. I may need to remove them to get to what's underneath. I don't mind doing the work (and feel that I'm learning a little something along the way) but I don't want to make things worse by fiddling around.

 

[Paul Birkeland]

The board above the D socket could be bypassed as it's very unlikely to be causing your problem.  Are the Kreg voltages on that board about equal?

 

[nipsy]

with all the boards hooked up I get the following KREG results:

(I have the black alligator probe clipped to the ground tab and am using the red probe to touch the board.)

KREG A -- 7.9
KREG B -- 10.5

I've gone through everything else with a fine toothed comb and reviewed all the connections in the manual and cleaned up a few more solder joints. The results of my latest testing are essentially the same.

Do you think the KREG could be the culprit ?

 

[Paul Birkeland]

No, if they were wildly different that could indicate that one of the current regulators on the forward board wasn't working properly. 

 

[nipsy]

Thanks again for all your help. I think I'm going to send it in for the repair service.

I'll be very curious to see what silly thing I missed that's been causing this problem...you will reveal that, won't you ?

 

[Paul Birkeland]

This kit arrived for repair and I found some PC board damage on the front board around one of the 2N2222 transistors.  I installed a bypass jumper to connect the emitter of the 2N2222 back to ground, and now the voltages are proper and this Eros is functioning properly.