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Smoke and white flashes (Read 4318 times)
nimrod
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Smoke and white flashes
07/01/12 at 18:11:05
 
On first time power up I got some white flashes and smoke.  There is now a charcoal colored line along a trace at the center of the board.  On inspection I found I forgot to jumper the shield to ground.  Is this worth pursuing or should I order a new board and start over?

Thanks

Nimrod
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MattG
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Re: Smoke and white flashes
Reply #1 - 07/07/12 at 21:05:09
 
that sucks, nimrod!
have you tried installing the ground jumper, see what you get?
depending on where/how the trace is compromised, it might be possible to jumper it as well?? depends...
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mboxler
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Re: Smoke and white flashes
Reply #2 - 07/08/12 at 13:20:45
 
Before I power mine up for the first time, which jumper are you guys referring to?  The 2008 assembly manual contains this instruction

Also don’t forget to install a jumper between the circuit ground and the board shield (ground plane). There is no specific location marked for this jumper.

This seems to refer to an older PCB, but...

Mike
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MattG
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Re: Smoke and white flashes
Reply #3 - 07/10/12 at 18:43:55
 
yeah the 2011 PCB and 2008 assembly manual board picture do not jive...I think as long as you ground the "chassis gnd" you'll be ok...

as for the OP's problem, the manual implies if you didn't ground properly you'd get oscillations/hum/noise, not a nuclear meltdown...I'm wondering if perhaps he missed one of the other jumpers the board needs?? I doubt Decware is shipping the old versions of the board anymore...
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nimrod
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Re: Smoke and white flashes
Reply #4 - 07/26/12 at 18:42:30
 
It looks like the trace going from J2 to a 1K 2W resistor is shorting to an adjacent ground trace.  I'll try bypassing the trace with hook-up wire and see what happens.

Nimrod
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MattG
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Re: Smoke and white flashes
Reply #5 - 07/27/12 at 05:32:09
 
Huh...looking at the board, the trace on one side of J2 is on the opposite side of the board from a ground trace, so it shorted *thru* the board? eesh...did you find any wiring mistakes that may have led to that? That would suck if it showed up with that flaw...

anyhow, hopefully a jumper will do the trick...it does sound like you'll need to scrape off the J2 trace at some point to open that short to ground...

I hope it's recoverable! good luck!
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dank
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pair of dual 18
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Re: Smoke and white flashes
Reply #6 - 07/27/12 at 12:09:28
 
Check the polarity of the big electrolytic capacitors.  If one is in backwards it would flash and smoke.  It may even be shorted now.

Dan
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nimrod
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Re: Smoke and white flashes
Reply #7 - 07/27/12 at 18:31:19
 
Capacitor polarities are correct.  Looks like there might have been a solder bridge to a resistor pad on the bottom of the board, even though I did check continuities after each solder.  I will be opening the J2 trace with a Dremel to de-energize it.  I'll let you know how things progress, but at some point I'll be tempted to go to point-to-point wiring instead of the PCB.  Its difficult to see whats happening in real time with traces on both sides of the board.

Nimrod
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nimrod
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Re: Smoke and white flashes
Reply #8 - 08/03/12 at 23:54:25
 
Does anyone know the purpose of the two additional 0.1 uF 400V caps that are on my PCB but not in the schematic or PCB image posted on this site?

Nimrod
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mboxler
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Re: Smoke and white flashes
Reply #9 - 08/04/12 at 04:25:28
 
Are you referring to the Hazen (CCE) mod?

http://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1245362440

Mike
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nimrod
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Re: Smoke and white flashes
Reply #10 - 08/06/12 at 17:57:17
 
If it is the mod, then it is on the PCB I have (Rev 9, 2011).  Has anyone else built on this board?   I was measuring the output of the Edcor (XPWR107-120) disconnected from the PCB.  I get 650V between the two reds (vs. 600V specified) and 330V between red and center tap (vs. 300V expected).  Is this within tolerance?  Between the filament browns I get 6.5V (vs. 6.3V specified).
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« Last Edit: 08/06/12 at 17:59:20 by nimrod »  
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mboxler
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Re: Smoke and white flashes
Reply #11 - 08/07/12 at 03:00:23
 
Hi nimrod...

I have the same PCB, and the same Edcor's.  Mine actually measured 345-0-345 disconnected.  Connected, they measured 330-0-330.  I got 6.9 on the brown wires, but it dropped to 6.5 when connected.  Edcor says they add a 5% load factor.  

I'm still working on mine...MattG had similar voltages on his.  It's the other voltage checkpoints that are important.

Mike
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nimrod
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Re: Smoke and white flashes
Reply #12 - 08/07/12 at 17:26:24
 
Thanks for the feedback Mike.

Nimrod
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nimrod
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Re: Smoke and white flashes
Reply #13 - 08/10/12 at 00:04:56
 
Update -- I wired over the J2 trace directly to  the 1K 2W plate resistor and opened the trace with a Dremel.  Now the PCB arced and smoked at the point where my bypass wire attached to the plate resistor.  The challenge continues.  Now I'm disassembling and individually testing all of the components, which so far have checked out OK.

Nimrod
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nimrod
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Re: Smoke and white flashes
Reply #14 - 01/21/13 at 19:31:11
 
I just completed point-to-point assembly using the schematic on this site and the amp fired right up.  Running through Polk Audio book shelf speakers there is plenty of volume.  There is a very slight hum which is only noticeable between tracks but I haven't put in the center tap fake for the Edcor heaters yet.  Sound quality is very good and I look forward to A/B testing against my Dynakit ST-70 push-pull.  I'll post pics when I get the final clean up completed.

Nimrod
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