[Elecraft] K2 Only 30-metre Band Works

[Don Wilhelm]

Murray,

The 7.6 volts on the 8 volt power rail is not a problem.
The relays operate on 5 volts output from U1.

It is possible that the relays have developed oxidation - if there is 
any damage to the relay case.  Otherwise, the relay contacts should be 
good - they are good for more than 100k operations.

Try the proper bandpass filter alignment.  Follow the band order shown 
in the manual - it is important.  The inductors must be aligned before 
the capacitors (to do otherwise will end up with you 'chasing your 
tail').  If you do not have indicated power output, put your RF Probe on 
W6 and align the bandpass filters for maximum RF voltage on each band.

73,
Don W3FPR

On 7/2/2021 8:54 PM, VA1CQ wrote:
> Hi Geert,
>
> Coincidentally, while troubleshooting today I was listening to relays! 
> There is a different sound depending on whether one relay clicks or 
> more than one clicks. Yes, there are relays clicking as I change the 
> band. A different number of relays operate depending on which band you 
> change to. The schematic shows which relays close as you change bands. 
> I was suspicious that maybe the necessary relay contacts were not 
> closing. If there is relay closing trouble, this could explain why the 
> different bandpass filters are not working correctly.
>
> Some history. I bought this K2 new in 2008. It sat unbuilt for about 
> 10 years. I then built the Control board only. After that a couple 
> more years passed. Just this year I built the Front Panel and RF 
> boards. Therefore all parts are at least 13 years old. I wondered if 
> over that time perhaps the relay contacts may have aged through lack 
> of use.
>
> Today I now have 80, 30 and 15 metre bands working. I was able to tune 
> the matching bandpass filters to get the correct transmit output power 
> on each of these bands. But I still cannot get 40, 20, 17, 12 and 10 
> metres to function. I did some resoldering and even took off the 
> heatsink to examine the underside of the RF board.
>
> I did more voltage checking today. I came to no conclusions but I 
> still am wondering why the 8 volt bus is only 7.6 volts and whether 
> this could be an issue or possibly cause unpredictable switching.
>
> I will continue studying the relays further in my next troubleshooting 
> session.
>