Cracks' Voltages are Off (LED Issue?) [resolved]

Interlukens1 · 582

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Offline Interlukens1

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on: April 25, 2020, 01:01:44 PM
Hey all! 

I just finished by first Crack build (had a blast, planning on doing more!), but had some issues with the first voltage test.  I had 2 voltages that were off and the A8 LED was not lit.  The wire wound resistors under the vent were pretty toasty too.  I've checked the wiring, which appears to be good.  I've re-flowed some suspect joints.  All capacitors, rectifiers and LEDs are oriented properly.  I've been reading that a faulty LED can do this. 

Here's what has happened so far:

1st voltage test:
Blew the fuse.  I suspect it was because my multimeter was accidentally set on current rather than AC volts, which I've been told can blow it.  Got some new 1A 250V slow blow fuses and used the correct settings.  Got 122.5V out of the wall (USA) on two measurements.  Proceeded with the build. 

Glow test:
Worked well.  Both tubes glowed, both halves of the 12AU7 glowed too. 

Secondary transformer test:
Got the expected values of 6.56V and 177.5V

Resistance checks:
All checked out on 3 different measurements- I'll save you the read. 

Voltage checks:

A8 LED is out and only half of the 12AU7 glowed. 

1 152.7V (expected 50-100V)
2 169.3 V (expected 170V)
3 0V (expected 0V)
4 169.3V (expected 170V)
5 78.7 V (expected 50-100V)
6 0V (expected 0V)
7 151.5V (expected 90-115V)
8 0V (expected 0V)
9 101.8 (expected 90-115V)
10 0V (expected 0V)

Is this an LED issue?  Did I miss something?  Thanks everyone!

UPDATE:
I'm thinking it's not the LED.  I did a continuity test on both LEDs and they light up.  Must mean I've screwed something else up. 
« Last Edit: April 25, 2020, 02:48:50 PM by Paul Birkeland »



Offline Paul Birkeland

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Reply #1 on: April 25, 2020, 01:51:13 PM
Glow test:
Worked well.  Both tubes glowed, both halves of the 12AU7 glowed too. 
A8 LED is out and only half of the 12AU7 glowed. 
You aren't passing the glow test anymore.  The solder joint at A5 looks nonexistent.  That joint not being well soldered would explain the issues you're having.

I would reflow any joints that remotely resemble that particular one. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Interlukens1

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Reply #2 on: April 25, 2020, 02:48:13 PM
Excellent catch!  A5 was indeed loose.  Secured that and re-flowed some more.  All voltages now in spec.  Thanks so much for the quick reply!