Voltage check assistance [resolved]

[phatfish]

Hi there, I could use some assistance as to where to look for issues. 

Checks during the build passed.

Resistance checks pass
All 12 LED lit

IA 217.6 OK
IB 217.2 OK
OA 213.1 HIGH
OB 214.5 HIGH
OC 60.3 LOW
OD 55.97 LOW
OkA 64.1 LOW
OkB 59.7 LOW
OkC .004 LOW
OkD .004 LOW

Many thanks for looking.  :-[

 

[phatfish]

Added a couple of build pics to start.  A + B sockets and top of C4S. 

 

[phatfish]

Socket C and bottom of C4S

 

[Paul Birkeland]

Can you very carefully measure the DC voltages at pins 4 and 5 of one of the front two sockets? (you don't need to do both)

On the front C4S board, that looks like either lead free solder or very low heat, possibly both. 

 

[phatfish]

Thanks Paul.  I assume that should be measured with the c4s hooked back up and all tubes?

For what it’s worth I’m using cards Quad Eutectic and a Weller station set at 680f and I’ve soldered a crack + speedball in a similar way with success.  Don’t mean to imply that I’m not butchering it, just giving more information.

Do my IA/IB numbers mean the boards behind the C4S are working ok?

 

[Paul Birkeland]

You need the tubes in there, not necessarily the C4S.  I'd turn the heat up a bit if you can. 

 

[phatfish]

A4 was ~58v.  Seemed to be slowly climbing starting at 57.3 and moving to 58.2 when I turned it off.  Should I leave it on to see where it settles?

A5 was ~51v.  Similar slow climb and I turned it off pretty quickly.

Measurements taken with the C4S board hooked back up btw. 

 

[Paul Birkeland]

Well that is extremely helpful.  I would set your iron as high as it goes, then reflow all the solder joints on that C4S board aside from the LEDs (they don't take much heat to solder properly and they aren't appreciative of reflow efforts).  Concentrate especially on the middle lugs of each of those MJE350 transistors, as they are reluctant to flow out properly without a bit of dwell time.

 

[phatfish]

Thanks Paul, I'm on it!  Iron set at 850f.  Mind sharing what this means and what voltages I should be seeing at A4/5?

Any theory on why I'm having issues with my joints on this board and not previous ones? 

 

[phatfish]

I reflowed all but the LEDs on the C4S board, and I basically have the same voltages.  :-\ 

Of possible note many of the discrepancies side to side seems to have switched from before (OC vs OD for example)

Here are my new values and some updated shots of the C4S board.

IA 217.8
IB 216.8
OA 215.2
OB 214.1
OC 55.91
OD 60.0
OkA 60.0
OkB 64.0
OkC .004
OkD .004

 

[Doc B]

What's with the center leg of what looks to be Q2A? I see a hole where there should be a lead with solder filling in the pad on the underside.

 

[phatfish]

I took the board bottom from two angles for this reason.  No soldering was done between the two pics.  It does really look like a hole from the 1st pic!  But check out the 2nd bottom pic  (board is flipped).

Sounds like you guys are quite sure the issue is on this board?

 

[Paul Birkeland]

You have the 10.7K EQ resistors installed in the servo sense area of the circuit rather than the 174 ohm resistors that belong there.  This is both preventing the EF86 tubes from drawing current and your EQ will be way, way off.

 

[phatfish]

CRAP!    Thank you!  Very glad I pointed those numbers facing up. I get these switched around this evening.    Order some new ones since I need the longer leads in the EQ section.

 

[phatfish]

Would it be possible to check my voltages without the EQ resistors in place while I wait for replacement 1072F's with the lead length I need?

i.e.
1740F's on the C4S board.
No 1072F's in place.

 

[Paul Birkeland]

Yes, all the DC voltages will settle where they are supposed to be with no EQ installed.

 

[phatfish]

Remeasured with the correct resistors in place.  I'm a tad low on the OC/OD/OkB values but well within 10% (although I'm on 120vac).

IA 217.0
IB 216.6
OA 166.1
OB 168.0
OC 93.8
OD 92.7
OkA 95.4
OkB 94.3
OkC 1.521
OkD 1.528

Honestly, I had difficulty with the replacement and was pretty sure I butchered a solder pad.  Guess it must be working ok...  I passed the resistance checks before doing the voltage ones.

 

[phatfish]

I'm up and running and it's sounding awesome!  8)

Many heartfelt thanks for the troubleshooting assistance and for spotting my resistor foul up.  Y'all rock.