[Elecraft] K3 Power Reading/SWR/ALC Problem

[Don Wilhelm]

Paul,

The diodes are the most likely suspect, so replace them first and re-check.

You are correct that the problem is that the wattmeter is not feeding 
the power back to the MCU and the power becomes uncontrolled.

Wattmeter damage is normally a result of static coming in on the antenna 
feedline.  If you do not have an means of disconnecting the antenna when 
not in use, it would be wise to add that - switching the K3 to a dummy 
load would be a good addition too.

73,
Don W3FPR

On 1/21/2018 1:39 PM, Paul Christensen wrote:
> Dick & Don,
> 
> Thanks for confirming.  Although unlikely to be the source of trouble, It
> also appears U6 and U8 are in the VFWD and VREF circuit paths.  I'll order
> up everything and have it on hand when I replace this week.  It could also
> be a passive problem like a marginally-corroded connector, or failed
> resistor.
> 
> By the way, the problem manifests with high SWR and power set readings that
> no longer match anything close to  actual output power into known good
> loads.  The SWR reading fluctuates excessively with change in the PWR
> control and slight changes in the control quickly lead to 120W power spikes
> when the K3 display indicates 15-20W.  This tells me the ALC circuit is not
> getting a good forward power sample.  So, it appears the SWR bridge or
> surrounding circuitry has partially failed.