[Elecraft] KPA500 Heat when powered off

[Ron Durie SIL.org]

Thanks Don,
That helps to further explain the design criteria and makes perfect sense.  

Ron Durie
IT BUYER JAARS INC
704-843-6011

-----Original Message-----
From: Don Wilhelm [mailto:w3fpr at embarqmail.com] 
Sent: Saturday, July 30, 2011 9:16 PM
To: Ron Durie SIL.org
Cc: Elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500 Heat when powered off

Ron,

The KPA500 has a POWER ON/OFF input.  In order for that to function, 
there must be some part of the KPA500 active, and those active circuits 
will generate some heat, however slight that may be.  Your towel 
concentrated that heat and made it obvious.  If you were to cover your 
"instant-on by remote" TV in the same manner, you would see the same 
effect - something has to be running to obtain that "on by remote" 
function, and that will generate some heat.  Yes, the rear panel switch 
turns all of those circuits off (but you cannot turn it on remotely).

73,
Don W3FPR

On 7/30/2011 8:51 PM, Ron Durie SIL.org wrote:
> I noticed when I covered my KPA500 with a towel, the next morning It feels
> slightly warm on the bottom and top over the Transformer.
> I thought that was curious since it had been off all night.
>
> I turned the power switch off on the rear panel and the heat went totally
away.
>
> I wondered if there are circuits running even with the front panel power
switch
> off.
>
> I checked the schematics and T3; BRIDGE; U2; U1; U4; and other circuits are
live
> with the front panel power switch off.
> This is normal and to be expected given the design.
>
> I have concluded that the switch on the rear panel is important for removing
> power totally from the KPA500.
> This is good to know when there are storms in the area, etc.
>
>