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Tech discussion => 4K,6K,8K Series => Topic started by: jwhmca on March 03, 2016, 11:37:05 PM

Title: Massive burn on CF82E75 card (plasma HT card)
Post by: jwhmca on March 03, 2016, 11:37:05 PM

Hi Guys,

we had a massive PCB burn on the CF82E75 card bargraph HT card... Any thoughts has to why this would happen?

It looks like it was around the two LARGE resistors and heatsinks

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: StarF666 on March 04, 2016, 01:48:05 PM

Can you see what exectly is burnt? R16 and D7 are there for protection.

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: jwhmca on March 04, 2016, 06:59:59 PM

R9 for sure... and pretty much everything around it.

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: StarF666 on March 04, 2016, 08:19:09 PM

Not sure but I would check the two TIP150 (TR4, TR5) and the two diodes D6, D7 and make sure there is no short from the cathode drivers (across C2). After repair I would start without meters attached and then add 8 at a time just in case.

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: jwhmca on March 04, 2016, 09:49:11 PM

yeah, that sounds about right... they are really burnt up anyway, so I'll need to replace everything. Anyone have a spare card they want to sell?

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: Dan Korneff on March 11, 2016, 02:11:11 AM

I had the exact same thing happen over here. I pulled off all the components in the affected area, cleaned up the PCB, and reinstalled components.
Even though most of the components looked pretty fucked, everything measured properly except for the big resistor that burned.
https://www.instagram.com/p/-OmM3CuArc/?taken-by=dankorneff
Look familiar?

Here's the replacement I bought:
http://www.ebay.com/itm/CLAROSTAT-VC10F-RESISTOR-1-1-K-0HMS-10-WATT-NNB-/390231309072?

1.1K 10W wirewound

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: Dan Korneff on March 11, 2016, 02:15:40 AM

as to what caused it, I'm chalking it up to old age. That resistor gets 275volts jammed thru it 24/7. Eventually it's gonna give up.

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: jwhmca on March 25, 2016, 01:41:12 PM

Looks like I will need to etch a new PCB, anyone care to take some "square" straight down photos of the front and back for me?

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: MarconeMusic on November 04, 2017, 03:05:06 PM

I Know this is old, but the EXACT same thing happened to me on mine last night... over night..
I came in to a "resistor burning" smell.... Searched and searched, Couldnt find it.. Started mixing and the meters werent working right...

Looked at the back and there was a BRIGHT orange glow from that R9 resistor..... Needless to say, the card is scorched and most of the traces over there are gone....

Anyone ever take a pic of a good one so i can get this remade?

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: xmax on November 08, 2017, 02:37:53 PM

I'm dealing with a desk that has NO meters, the PCB looks like
it has been warm but nothing is fried looking. All the transistors
tested ok, but obviously I missed something...

Title: Re: Massive burn on CF82E75 card (plasma HT card)
Post by: MarconeMusic on November 10, 2017, 06:32:49 PM

I fixed mine. 
Replaced both tip150s and the 1.1kohm and the 39k resistors. Plus 3 diodes in the same section. 

Works like a charm.