[Elecraft] K2 ..K2 100w ATU .. hirefl current error and then over current failure

[Don Wilhelm]

All quite logical - it seems you always have full power output (and then 
some more too).
My best guess is that you have damaged the diodes D16 and D17 in the 
KPA100, and you are always transmitting at full power - which may be far 
in excess of 100 watts.

In other words, your KPA100 does not throttle back to 20 watts when 
tuning, it tries to tune at full power - and too much of that can cause 
burned relays in your KAT100.

The resettable fuse in the base K2 is also tripping due to high current 
required by the base K2 PA transistors - stop trying to transmit until 
you get those diodes fixed, you could cause further damage because 
everything is running at "full tilt".

Do you have an external wattmeter and a dummy load around somewhere?  If 
so, connect them to the KPA100 (no KAT100) and set the K2 power at 3 to 
5 watts (use 40 meters).  Do a TUNE and observe the power indicated on 
the external wattmeter.  If it is above 12 watts, then you have 
something not working in the KPA100 wattmeter, and damaged diodes is the 
most likely cause.

If you are not in the habit of removing the antenna from the K2 when not 
in use, know that it only takes a nearby lightning stroke to stress 
those diodes, and they are also susceptible to damage from rain static, 
wind static and snow static.  Get a DC discharge path across all your 
antennas to help, but disconnect the antennas when not in use is your 
best insurance.

73,
Don W3FPR

On 1/12/2012 3:49 AM, stephen pearce wrote:
> Does anyone recognise this pattern ..
> k2 100W
> kat100 (rev b board)
>
> ..
> apparently intermittent error ...
> initially hirefl current error on auto tuning ...
> then overcurrent failure of power supply when auto tuning at high current ...
>
> rx working fine ... in kat100 ant1/ant2 relay seems to be ok .. as is
> hi/low current relay
> and all the L and C relays for the auto tuner seem to click in
> appropriately when you run through them in the set up menu on the k2
>
> I've inspected the board in the kat100 and there are no obvious dry or
> loose solder joins ...
>
> If you tune at sequentially higher power settings starting at 0.1,
> then just under 10 (so as not to trigger the high power relay )
> then just above 10w then 20+w .. then full power it seems to avoid the
> over current failure of the supply ..
>
> Why the supply (which is mfj4125) is cutting out (it must have a
> resettable fuse as it recovers  after about 30 sec) puzzles me ..
> previously I have observed the k2 shut itself down before this happens
> .. and makes me wonder if rf is getting into the supply ..
> particularly if there is an initial significant mismatch in the atu
> before it completes its auto tune
>
> I have tried "init" reset in the k2 atu submenu .. as well as the cal
> routines ...
>
> tried transmitting into dummy load and into antenna ...neither seems
> to make a consistant difference ...
>
> possibly there is a fault in the fwd/refl power sensing in the atu ..
> but this should not produce over current cut out in the supply
>
> (this k2/kat100 is a friends ...I tried substuting my kat100 .. which
> seems to work ok with his k2)
>
>
> Any suggestions appreciated ...
>
> 73s
> zl1any
>
>