[Elecraft] KSB2 problems in K2 transceiver

[Don Wilhelm]

Mark,

When you have the problem, look at the voltage at P1 pin 6 (that is 
VRFDET signal)?
If that is high, the MCU will limit power drastically.

Make sure Q1 is properly oriented.  If that does not help, try a mod to 
the KSB2 - reduce R9 to 1.5k and cut the trace between P1 pin 6 and the 
base of Q1 (on the top of the board) and insert a 1k resistor across the 
trace cut.
That will calm ALC problems with the KSB2, and otherwise will do no harm.

73,
Don W3FPR

On 5/8/2021 1:44 PM, M Bak wrote:
> Today I finished the KSB2 adapter and installed it into my K2. It worked
> first time but was intermittent. I found the issue as I had omitted to
> solder the outer top pins of the twin three pin interconnects. That done
> everything seems ok and then........
>
> No Apparent RF output. USB/LSB/CW Pressing TUNE produced a max of 0.8W. VOX
> would trip to transmit but the S meter showed no modulation. Coarse carrier
> balance adjustment worked but zero S meter readings was very wide (unlike
> earlier when it was a fine, narrow adjustment)
>
> All voltages looked slightly low but ball park on the KSB2 board except for
> U2 (the DAC) Pin5 which is ALC THR. This was sitting at 5.89v rather than
> 0.6 on both RX and TX.
>
> I have removed the KSB2 and full CW power output can now be achieved which
> is a relief.
>
> I will examine everything under a microscope again but has anyone any
> suggestions? I suspect ALC to be the culprit but how to investigate?
>
> Thanks
>
> Mark G4RUR
>