[Elecraft] K3S Hi Sig and sluggish performance

[Michael Carter]

Hi Joe,

The persistence of the HI SIG warning after power cycling the rig is not a good sign.  The HI SIG warning is triggered by excessive current in the post-mixer amplifier, and the MCU responds to that excess current indication by turning off the preamp and, if necessary, turning on the attenuator.  I can't explain the sluggishness of the response to front panel controls short of a portion of the internal bus communication being corrupted.

I am hoping Keith, WE6R may have seen this particular issue in rigs sent in for repair.  If I were to look for a hardware fault, I would start with measuring the voltages on the post-mixer amplifier transistors Q8 and Q9 on the RF board, and in particular look at the voltage on R145 (labeled as VPOST on the schematic). The VPOST voltage is the sensed quantity that triggers the HI SIG warning.  I don't know if these components are accessible from the top side of the RF board or not - you can probably tell from opening the top cover presuming you don't have the sub-receiver installed in your K3S.

Perhaps you can comment in more detail about the sluggishness issue - are all front panel controls sluggish in response to button presses?  Do the VFO A and VFO B knobs when turned result in immediate changes in the displayed frequencies?  Does the receiver respond audibly to switching the preamp options and attenuator on/off?

Thanks, and 73,
Mike, K8CN