K2-100 ATU

[Elecraft mailing list]

Hello Elecraft,

After a couple of years of flawless operation my K2-100 ( separate units) is starting to act up.:

A) At first I noticed that when pushing the “tune” key, that ATU of the 100 watts unit caused the relays to clatter in the normal way
but after finding the 1:1 setting, the tuning condition was not concluded, and I had to switch off the set completely and start anew.
Mostly it went well and the tune condition stopped automatically, as it should.

BUT

B) To-day pushing the “tune” key did not cause the built-in ATU of the 100 watts unit to start its clattering.
The SWR  reading ( lights)  went all the way to the right, and stayed there.
Naturally I switched off the set instantly , while in a split second I noticed the “Hi-current “ displayed.
Using the Ant 2. position going to a 1000 watt dummy-load did not change the malady..
++++
Disconnecting the 100 watt unit completely, I set up the K2 in its barefoot condition.
The built-in ATU of the K2 worked completely normal.
++++
Conclusion: Presumably something has developed in the SWR circuits of the 100 watt unit.
Where should I look ?

73’s OZ5RB

Hans Elfelt Bonnesen
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[Don Wilhelm]

Hans,

The most common cause of that kind of failure is that the wattmeter
diodes in the KPA100 and/or The KAT100.

One quick way to check the KPA100 is to remove the KAT100 and connect
only the KPA100 ANT jack to an external wattmeter and also a dummy load.
Then do a TUNE and see how much power is actually being developed.  Set
the power to 50 watts.
If it is 20 to 25 watts, the KPA100 wattmeter is working properly.  But
if it is 120 watts or more, diodes D16 and D17 in the KPA100 need to be
replaced.  They are 1N5711 type.

You may also want to arbitrarily replace D1 and D2 in the KAT100 - they
are the same type.  So if you have to order them, order quantity 4.

The most common cause of those diode failures is a static surge on the
antenna feedline - likely from nearby lightning.

The other cause of that kind of SWR indications is a failure of ATU
firmware Pin 3 or 4 or both.   That IC can also be damaged by static surges.

The HiCur message is also associated with the failure of the KPA100
wattmeter diodes, because that is where the power is controlled from,
and the K2 MCU does not know that any power is being developed, and
pushes the drive power to the maximum.
That also stresses the base K2 PA transistors and if not caught in short
order, will cause their failure.

73,
Don W3FPR


On 9/28/2018 4:40 PM, Hans Bonnesen via Elecraft wrote:

> Hello Elecraft,
>
> After a couple of years of flawless operation my K2-100 ( separate units) is starting to act up.:
>
> A) At first I noticed that when pushing the “tune” key, that ATU of the 100 watts unit caused the relays to clatter in the normal way
> but after finding the 1:1 setting, the tuning condition was not concluded, and I had to switch off the set completely and start anew.
> Mostly it went well and the tune condition stopped automatically, as it should.
>
> BUT
>
> B) To-day pushing the “tune” key did not cause the built-in ATU of the 100 watts unit to start its clattering.
> The SWR  reading ( lights)  went all the way to the right, and stayed there.
> Naturally I switched off the set instantly , while in a split second I noticed the “Hi-current “ displayed.
> Using the Ant 2. position going to a 1000 watt dummy-load did not change the malady.

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