[Elecraft] [K3] Strange Selective Hearing in My K3

[Brian Hunt]

Sounds like a thermal problem, possibly with the 8v regulator. I have a problem with my K3 (S# 4K range). If the rig is cold ~60 F the 8v apparently goes out of regulation evidenced by the display illumination dimming on key down. The rig works normally otherwise. The problem goes away once the FP Temp warms a little - I wrote the number down somewhere but can’t find it now. 

Good luck & 73,
Brian, K0DTJ

> On Oct 10, 2022, at 09:49, Michael Carter <Mike.Carter at unh.edu> wrote:
> 
> Hi Eric,
> 
> I'm voting with my friend Dave, K1WHS,
> for looking first at the voltage regulators.
> 
> The 8 volt regulator supplies the TC4427
> gate driver IC, which in turn provides 7R/7T voltages
> separately to the Transmit and Receive switching circuits.
> The loss of the 7R/7T voltages would disable the
> PIN diode T/R switches and render the radio deaf
> and unable to transmit.
> 
> If the 8 volt regulator doesn't collapse after some
> time observing its output voltage, I would check
> the TC4427 (U11 on the RF Board) to be sure its
> outputs are correct (the 7R/7T voltages).  The
> regulator is likely the first culprit - its '8A' output
> pin provides power to a large number of circuits
> in the radio.
> 
> 73,
> Mike, K8CN
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