[Elecraft] FW: KPA500 faults

[Charles K0MV]

Hi William,

"

surmise it was heating

"

Consider as the surface mount current sensing resistor (assuming it is 
surface mount)

is made to withstand solder reflow it seems unlikely to be heat. I've 
had many surface

mount resistors develop hair line cracks due to vibration and board 
flexing (in breadboards I built).

In failures I've seen due to heat, the resistor visibly changes color 
especially in markings, white to

brown.

As long as you have the unit opened up, perhaps you should take a lupe 
or magnifying glass, bright

flashlight and just look around for other cracks in components or solder 
joints.


I hope I can work you on 40M FT8, I need VP2E.


Good luck

Chuck K0MV


On 3/3/22 08:40, Dr. William J. Schmidt wrote:
> Sorry guys, this is not a trivial line voltage problem.
>
> The 60V line to the PA does not sag that much (starts at 72V goes to 60V
> under FULL LOAD as measured at the PA)... it's in the voltage divider for
> the 60V/32 line or the connectors that carry it to the front panel processor
> for digitizing.  Changes with heat load.  This amp is in the Caribbean and
> there is plenty of excess heat and corrosion. (nb. I just replaced the
> current sensing resistor in my K3S for the 100W module due to a hair-line
> crack... surmise it was heating).
>
>
> Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
> VP2EHZ
>
> email:  bill at wjschmidt.com
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
> Behalf Of Naumann, Robert, W5OV
> Sent: Thursday, March 3, 2022 9:11 AM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] FW: KPA500 faults
>
>
> What line voltage are you running it on?  If you're not on 240v, switching
> to 240v would be the easiest and most effective improvement.
>
> Doing so yields a 4:1 improvement in line voltage regulation / reduction in
> voltage drop.  Double the voltage, at half the current draw.
>
> 73,
>
> Bob W5OV
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
> Behalf Of Dr. William J. Schmidt
> Sent: Thursday, March 3, 2022 00:39
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] KPA500 faults
>
> I have a KPA500 that faults on low (60 VDC) voltage.  After measuring the
> power supply voltage at the PA module is perfectly fine.  The voltage read
> by the processor on the front panel via pin 10 of P1 is lower than it should
> be and hence the fault condition.  I suspect there is a voltage divider on
> the LPF board that drops the 60 VDC to something that the processor can read
> and digitize (in the 0 to 3-5 volt range).  The set of schematics I have do
> not show the voltage divider anywhere. does anyone have this part of the
> schematics for the KPA500 so that I can adequately troubleshoot this amp and
> get it on the air for the contest this weekend?   Multiple notes to Elecraft
> have gone unanswered.
>
>   
>
>   
>
> Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
> VP2EHZ
>
>   
>
>   
>
> email:   <mailto:bill at wjschmidt.com> bill at wjschmidt.com
>
>   
>
>   
>
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-- 
Charles K0MV