[Elecraft] K3S/100 very low TX power

[Wayne Burdick]

Ian,

This sounds like an intermittent connection somewhere, possibly in the 10-W amplifier stage. 

Try re-tightening all of the hardware on the bottom covers, including the screws that hold the PA device tabs to bottom cover B. Also try reseating the 10-W amp module. 

If this doesn't help, try measuring the 0-dBm drive at the XVTR OUT jack. For this purpose you need to put CONFIG:KXV3B into TEST mode.

If you get a full 0 to 1.5 dBm output at XVTR OUT (into a 50-ohm load), but low power output from the 10-W amp module, then the latter is probably implicated. Look at both sides of the module very carefully to see if a component is not soldered at one end, etc. This is rare but it can happen. 

Also look at the components on the RF board just behind the 10-W amp module.

I can give you more detailed signal tracing info if needed.

Wayne
N6KR



On Sep 12, 2015, at 1:57 PM, "Ian White" <gm3sek at ifwtech.co.uk> wrote:

> My K3S/100 has gone into an unusual state where the maximum power
> available - on any mode, any band - is about 1.5-2W. This is independent
> of any PWR setting above 1W, and the PA does not engage at higher PWR
> settings.
> 
> All this began on Friday afternoon when I switched on the rig. The K3S
> had been working normally a few weeks ago, but hadn't been used for
> transmitting in the meantime.
> 
> An external power meter confirmed that the TX could not deliver more
> than about  1.5-2W. This was  confirmed again by the failure messages
> from a TX power calibration. While troubleshooting, I progressively
> uninstalled the KPA3 followed by the KPAIO3A adapter board, but with no
> change. Even in the simplest 10W configuration with only the small
> bridge board in place between the two PA connectors, the K3S would still
> only deliver 1.5-2W with no effective PWR control.
> 
> I also tried most of the other common tests: unplugged everything else;
> reloaded an older saved configuration; EEINIT; reloaded the saved
> configuration again. No change.
> 
> But I also noticed that the firmware was one release behind the times,
> so for lack of any other ideas I did a complete firmware upgrade to the
> latest MCU 5.35 / DSP 2.86 / FPF 1.24 - and it started working again!
> Normal power output up to 10W, and fully variable up to 100W after
> reinstalling the PA module. Another TX calibration confirmed that
> everything was fine. 
> 
> That pleasant surprise seemed to indicate that the problem had been more
> related to firmware than to hardware.
> 
> By Friday evening, I believed the problem had gone away... but I should
> have known better. 
> 
> Today it has failed again, exactly the same way as before. Reloading the
> same latest firmware didn't work a second time.
> 
> So now it's the weekend and I'm all out of ideas.
> 
> While I wait until Monday to contact Elecraft Support, could anyone in
> the group offer any suggestions, please?
> 
> 
> 73 from Ian GM3SEK
> 
> 
> 
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