Neither LED is lighting [RESOLVED]

phigits · 1506

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Offline phigits

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on: March 03, 2019, 12:10:32 PM
Finished the basic Crack build and with the help of a friend who is an EE did a bit a quick troubleshooting to get everything powered up and glowing.  He went through everything on pages 47 and 48 of the manual using his high dollar fluke meter.  Everything measured as it should but I did not have the proper cables to get the dac that I currently have functioning so we could not do a sound check.  A quick trip to Frys and I returned with the cables and headphone adapter that i thought would allow me to enjoy some new sounds.  I plugged it all up and...nothing. Not a crackle, not a buzz, nothing.

I flipped it over again and checked the RCA jacks, headphone jack and volume potentiator.  It all looks good to me.  However, I did notice the LEDs - neither is lighting up. 

The DC voltages while the unit is on:
A3: 1.66
A8 1.66
Center Pin: .886
« Last Edit: March 04, 2019, 12:48:21 PM by phigits »



Offline Paul Birkeland

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Reply #1 on: March 03, 2019, 12:14:39 PM
If the LEDs don't light up, then you didn't pass your voltage checks.

You will need to measure terminals 1-10 and post any readings that are out of spec here. 

The solder joint at 3L is not well flowed and may be a decent contributor to your problem.  Seeing 0.89V at the center pin of the 9 pin socket confirms that your ground buss (string of black wires) is not adequately soldered together.  Another popular spot that seems to get missed is where the black wires meet on the headphone jack. Often times one of the wires will be well soldered to the jack but the other wire will be loose.

Pins 4 and 5 on the 9 pin socket also look inadequately soldered. 

You definitely don't want to attempt to listen to this amp until this is resolved.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline phigits

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Reply #2 on: March 03, 2019, 12:49:16 PM
I went back to the bench and and determined that my meter was attached to the wrong location - I am a software engineer which, as it turns out offers no transferable skills in this particular endeavor.  When the black alligator clip was reattached to a proper ground location, I noticed that both my LEDs are glowing as they should be.  DC readings this time (on my subpar meter) are:
A3 1.54
A8 1.55
Center Post: .7

I agree the solder at 3L looks shoddy and I will redo that joint.  I'm running out of time this evening but I appreciate the constructive feedback.



Offline Paul Birkeland

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Reply #3 on: March 03, 2019, 03:05:11 PM
I noticed that both my LEDs are glowing as they should be. 
Yeah, you have a loose wire or two in the amp that are behaving differently as they get jostled around a bit.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline phigits

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Reply #4 on: March 04, 2019, 12:52:33 PM
After digesting Paul's feedback, I went back through the black connections checking each one.  They were all OK but I did clean up a couple that seemed to have too much solder on them.  I got a much better meter and went through the voltages again.  Once again everything was in range.  Both LEDs were lighting up so I wired up the dac and the headphones and viola - crystal clear sound.  Not hiss, pop or buzz.  Burning it in now and happy as a clam.

Thanks to Paul for quick and accurate feedback.  And for not making me feel like a clown.