[Elecraft] K2 alignment problem at 10/12m

[Don Wilhelm]

Andy,

Are you peaking the inductors for 10 meters before you peak the trimmers 
on 12 meters?  That is the required order for the bandpass filters - of 
the band pairs, the inductors must be peaked first and then the capacitors.

On your 10 meter problem, check all the components in the Low Pass 
Filter again.  Re-count the turns on the toroids making certain you 
count the number of times the wire passes through the center of the core.
Normally high current messages combined with low power output point to a 
problem either with T4 or the LPF.

Does the power start to drop off on all the higher frequency bands?  
With a 13.8 volt supply, the normal power output from a well constructed 
K2 will be above 14 watts on all except 10 meters and possibly 12 
meters.  If the power drops off for bands below 12 meters, look 
carefully at T4 - the bare link wires should go straight through one 
hole of the core (not wrapped around).

When you find your 'scope probe, you can investigate the RF Voltage at 
various points along the transmit chain (build the RF Probe from the 
parts in the K2 kit if you can't find the probe, or it is not a 10X 
probe).  You can compare a working band with a non-working band at each 
point.

While looking at the RF voltage levels, keep in mind how the K2 does the 
power control - it samples the output, and if not up to the requested 
power, the microprocessor increases drive in an attempt to provide more 
output.  That means you will have HIGHER than the expected RF Voltages 
at every point that is OK - the problem will be found just before the 
point where the RF voltage drops substantially.
Set the power at 5 watts for that Signal Tracing, and refer to the 
Transmit Signal Tracing portion of the Troubleshooting Appendix in the 
back of the K2 manual for the expected values and test points.

73,
Don W3FPR

Andy Webster wrote:
> Hello all,
>
> First up I'd like to say what a superb kit the K2 is, I've really enjoyed the time spent quietly soldering away and the instructions are first class with some great finishing touches (all the resistors in sequence on a custom strip - what will they think of next!). It's a shame it's nearly over...
>
> Anyway, I have a problem on the final part of alignment. All of the lower bands seem fine on both pre-alignment (receive signals peaked for signal strength) and transmitter alignment (filters peaked for ~2W output) except on 12m and 10m bands.
>
> On 12m the receiver is very quiet (although I can hear a broadcast station to try and peak the filter against) and there seems to be little effect when adjusting C44 and C46. On transmit into a dummy load there is consistently only 0.2-0.3W showing.
>
> On 10m the receiver seems OK (receiving some strong CW) and L12 and L13 can be peaked for maximum response but transmit into the dummy load is hit and miss, sometimes approx. 2W, sometime it shows a High Current warning and displays around 10-15W before I quickly deselect Tune.
>
> Obviously these two bands share filters so my attention is drawn there but I thought I'd float the exact symptoms at the collective while I search for my 'scope probe. I've closely inspected the band pass and LPF areas for faults and resoldered all the joints just in case of a dodgy one to no avail. The number of turns on the LPF toroids is correct. Does the different behaviour of the two bands on tune tx indicate a more specific area for attention?
>
> Next step for me is to run a scope along the signal path but appreciate any thoughts as to schoolboy errors I have obviously made...
>
>