KSB2 problems in K2 transceiver

[M Bak]

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

--
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living in the past. If you are content you are living in the now.
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[Mike K8CN]

Mark,

Pin 5 of U2 provides ALC threshold voltage to the emitter of Q1 on the KSB2
board.  The 5.89 V you measured on Pin 5 suggests that the DAC input
register B didn't properly load the data word from the MCU.  I would check
the solder joints on all U2 pins and Pins 14, 16 and 17 of the MCU socket.  

73,
Mike, K8CN



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[Don Wilhelm-5]

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
>

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