[Elecraft] Deaf KRX3 on one band ...

[Joe Subich, W4TV]

Thanks, Ron.  It looks like it will be a pain to troubleshoot.
The cover is on the bottom of the receiver housing and I'm
not sure if the board is mounted "up side down."

Since I will need to pull the KRX3 just to troubleshoot, I'll
probably swap it into the radio on the bench for updating ...

73,

    ... Joe, W4TV

On 10/16/2010 5:10 PM, Ron D'Eau Claire wrote:
> Joe, the only element in the receiver dedicated to 160 meters is the input
> bandpass filter. It's the top one on the attached schematic (sent direct to
> your personal e-mail).
>
> Note that this filter covers both 80 and 160 and relay K2 changes two
> capacitors to tune it for each band. It seems like that K2 is not switching
> or that C81 or C82 (the two capacitors switched in to tune 160) are no
> longer in the circuit. It may be a problem with the switching command from
> U2.
>
> I'd start as follows:
>
> Open the K3 and exercise the connectors on the SUBIN and SUBOUT boards that
> connect the KRX3 module to the main K3 RF board. I'd do that first to ensure
> the module is fully plugged in and all the pins of the connectors is making
> good contact. The SUBOUT interface is particularly vulnerable to being
> dislodged since it's farthest from the supporting bumper on the back of the
> loudspeaker.
>
> If that doesn't do it, I'd switch the KRX3 to 160, power down and open up
> the KRX3 enclosure to see if both sides of C81 and C82 are grounded. Those
> are the two caps that resonate the filter on 160 meters. One side is always
> at ground through the inductors in the filter. The other side goes to ground
> through the relay when you switch to 160. If one or both are not grounded,
> Relay K2 is not switching. Either it's defective or it's not getting the
> proper switching signal from U2.
>
> 73,
>
> Ron AC7AC
>
>
> -----Original Message-----
>
> My KRX3 is deaf on 160 meters ... and only on 160.  I had not done
> any significant split on 160 since getting it (that one was off-line
> for a while until I replaced a heat sensitive VFO B encoder and made the
> updates).
>
> Yes, I've checked the antenna<G>  ... it's on same antenna as the
> main rx.  On every other band, signal levels are the same in both
> receivers (balance is centered when the receivers are tuned to the
> same signal) but on 160 there is almost nothing from the sub Rx ...
>
> It does not appear to be related to roofing filters as I've checked
> signal levels with both the 2.8 KHz and 400 Hz filters.  I've also
> rechecked the receiver gain alignment ... although those should also
> effect the higher bands and operation is normal other than 160.
>
> Any suggestions where to start looking - signal levels are normal
> on80 meters and higher as well below 1700 KHz (high end of the AM
> broadcast band - both receivers have BPF3 installed).
>
> 73,
>
>     ... Joe, W4TV
>
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