K2 Output issues in Tune

[N9AUP]

My K2 (#7235) recently started to have intermittent issues with power output in tune.  Sometimes I get the power I set for a given band and sometimes I don't.  Just now, if I set the level at 10 watts for each band, they all work as expected (with a little dithering in the 10ths position) when I press Tune except for 80 meters where I get 5 watts and 10 meters where I get 8 watts.  This morning I got 2.5 watts in 80 meters and returned later to find it spot on at 10 watts.  In each case, mode was CW and the vfo set for the cw section for each band.  Usually, if a band shows low power and I hold tune in for 5 seconds the output level will climb up roughly a watt.  I first discovered the issue last week when 15 meters went bonkers with the forward power waving up and down quite rapidly.  I immediately stopped, changed bands, saw normal behavior then went back to 15 meters and it was right where I had set it.  At that point, all bands were ok and no further problems were observed.  Yesterday, things were as described above.

I have been testing with cables running from the rig through the SWR meter and into the station dummy.  I did try an alternative dummy and checked the cables as well.

If all bands acted the same, I'd be looking for a bias issue.  Could there be something wrong in the relays?

George
N9AUP

[Geoffrey Mackenzie-Kennedy-3]

Hello George,

You asked if there could be something wrong with a relay or relays.

Some years ago I had a similar problem with my K2/100, but it appeared only
on 40m.  The cause was "dirty" relay contacts, rare in sealed relays, which
sometimes also caused the receiver's sensitivity to decrease significantly -
usually before transmitting..  The relay contacts in question were K1A (pins
3 and 4) located at the 40m bandpass filter.

- If - your problem is caused by a "faulty" relay, then it is unlikely that
any of the relays associated with the bandpass filters are to blame.  While
contrary to popular wisdom the contacts of a sealed relay can become
"dirty", the odds against this happening are very high, provided that the
relay's sealed casing has not been punctured (e.g. by a hot iron) before or
during the installation of the relay.  Because you have found the problem on
80m, 15m and 10m, at least three of the relays associated with the bandpass
filters would have to have "dirty" contacts - which is pushing the odds by a
large degree.

The same argument is applicable to the relays used to swirch the low pass
filters, which leaves the relays within the ATU.

To eliminate (or otherwise) one of the ATU's relays as being the cause of
the problem, I suggest that you disconnect completely the ATU and connect
your dummy load directly to the K2's antenna connector.  If the problem
persists, then an ATU relay is not the cause.

My gut feeling is that a solder joint has become intermittent.

Hope that you find the cause.

73,

Geoff
LX2AO


On November 30, 2012 at 3:37 AM, George N9AUP wrote:

> My K2 (#7235) recently started to have intermittent issues with power
> output
> in tune.  Sometimes I get the power I set for a given band and sometimes I
> don't.  Just now, if I set the level at 10 watts for each band, they all
> work as expected (with a little dithering in the 10ths position) when I
> press Tune except for 80 meters where I get 5 watts and 10 meters where I
> get 8 watts.  This morning I got 2.5 watts in 80 meters and returned later
> to find it spot on at 10 watts.  In each case, mode was CW and the vfo set
> for the cw section for each band.  Usually, if a band shows low power and
> I
> hold tune in for 5 seconds the output level will climb up roughly a watt.
> I
> first discovered the issue last week when 15 meters went bonkers with the
> forward power waving up and down quite rapidly.  I immediately stopped,
> changed bands, saw normal behavior then went back to 15 meters and it was
> right where I had set it.  At that point, all bands were ok and no further
> problems were observed.  Yesterday, things were as described above.
>
> I have been testing with cables running from the rig through the SWR meter
> and into the station dummy.  I did try an alternative dummy and checked
> the
> cables as well.
>
> If all bands acted the same, I'd be looking for a bias issue.  Could there
> be something wrong in the relays?
>
> George
> N9AUP

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