Re: [Elecraft_K3] KPA500 finals blown

Mel Farrer <farrerfolks@...>

As one who has seen the worlds fastest fuses go bang, the causes maybe many. 

Usually the higher VDC at load will not necessarily blow them unless it exceeds the max level by a considerable about. They just get hot.
The killer I have seen is a component failure in the parasitic suppression network that causes a fuse condition.
The fact that the temperature protection did not trip makes me not include it.

Look for a component failure.  Not the transistors.  I would not put in new devices until a through component be component investigation is done.  Mistakes get expensive.
Good luck.

Mel, K6KBE

From: "dalej dj2001x@... [Elecraft_K3]"
To: Elecraft_K3@...
Sent: Thursday, January 21, 2016 2:48 PM
Subject: Re: [Elecraft_K3] KPA500 finals blown

I'd be interested to know what the HV tap was set for, what the HV displayed for HV and if there happened to be a voltage surge or spike that came down the mains.  All that might contribute to sudden failure.  I doubt heat is a factor. 

Just a thought.

Dale, K9VUJ

On 21, Jan 2016, at 8:47, vu2nks@... [Elecraft_K3] <Elecraft_K3@...> wrote:

KPA500 shut off with a bang while operating RTTY @300W.

Antenna is a steppir beam.

On opening the KPA500,found 2 ceramic? caps of VRF2933

adrift with underside of the said caps,black.

I am in touch with Support.

Has anyone here replaced these devices? This will be my first time
working with power transistors.

73 and HNY,




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