Forums - Smoke and white flashes

nimrod Verified Member Posts: 14	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 Verified Member Posts: 30	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

Senior Member

Posts: 89

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

Verified Member

Posts: 30

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 Verified Member Posts: 14	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

Verified Member

Posts: 30

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 Seasoned Member pair of dual 18 Imperials Posts: 425	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

Verified Member

Posts: 14

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 Verified Member Posts: 14	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 Senior Member Posts: 89	Re: Smoke and white flashes Reply #9 - 08/04/12 at 04:25:28 Are you referring to the Hazen (CCE) mod? https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1245362440 Mike
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nimrod

Verified Member

Posts: 14

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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mboxler

Senior Member

Posts: 89

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 Verified Member Posts: 14	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

Verified Member

Posts: 14

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

Verified Member

Posts: 14

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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nimrod Verified Member Posts: 14	Re: Smoke and white flashes Reply #15 - 01/23/13 at 19:20:02 Fake center tap did the trick. No audible hum anymore. Only problem left is to figure out why the volume pot is not attenuating.
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nimrod Verified Member Posts: 14	Re: Smoke and white flashes Reply #16 - 01/24/13 at 21:55:43 Forgot to wire the pot grounds to chassis. Attenuation is fine now. Sound quantity and quality are so good I'm not in that much of a hurry to get the high efficiency speakers. --Nimrod
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mboxler Senior Member Posts: 89	Re: Smoke and white flashes Reply #17 - 01/24/13 at 22:10:18 Congratulations! Which Polk Audio speakers are you driving? Of course, pictures will soon follow ;). Mike
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nimrod Verified Member Posts: 14	Re: Smoke and white flashes Reply #18 - 02/01/13 at 21:39:08 The speakers are Polk R-1. I'm thinking I might try the Madisound speaker kit sometime soon. And attached are pics of the build in its still unpainted glory. Nimrod
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nimrod Verified Member Posts: 14	Re: Smoke and white flashes Reply #19 - 02/01/13 at 21:40:47 And here is "side B". --Nimrod
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mboxler Senior Member Posts: 89	Re: Smoke and white flashes Reply #20 - 02/02/13 at 14:39:29 Very Nice! Glad the title of your thread no longer applies. A single driver kit would be match made in heaven. Mike
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Real Verified Member Posts: 32	Re: Smoke and white flashes Reply #21 - 02/02/13 at 16:38:47 Very nice job. I'm still working on my case. Hoping to but it all together next weekend. Real
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