[Elecraft] My K2/100 keeps resetting at high power

[Don Wilhelm]

Hisashi,

OK, so that sounds like the KPA100 may be oscillating.  First things to 
check are the diodes in the T/R switch, the high voltage bias supply 
(check during transmit too) and the operation of Q6 and Q7.

Is this the newer KPA100 design with blue toroid cores at L16 and RFC1?  
If not, you will want to install KPA100UPKT, it was designed to combat 
an oscillation tendency.

73,
Don W3FPR

On 4/2/2012 8:19 PM, Hisashi T Fujinaka wrote:
> After getting the suggestions from Eric and you, I looked at the
> metering I have already.
>
> I don't think it's the SWR bridge because the power reading matches the
> wattmeter on my MFJ-1788. It steadily increases and looks about the same
> as what the K2 shows.
>
> However, the voltage/current meter I get to from the DISPLAY button is
> odd. As I turn up the power before the KPA100 kicks in, I get an
> increasing current up to 2.5. Then the current reading drops to 1.5 and
> stays there. The metering of my power supply shows increasing current
> and everything resets itself when it gets ~15-20A.
>
> Time to look for the schematics, but any suggestions would be
> appreciated.
>
> On Mon, 2 Apr 2012, Don Wilhelm wrote:
>
>> Hisashi,
>>
>> If by "reset" you mean the power turns off, you are most likely seeing the
>> internal resettable fuse trip.
>> Normally you would see a HiCur message too.
>> Usual causes for that behavior are either that the KPA100 wattmeter diodes
>> have been damaged or you have a damaged PA transistor in the base K2.
>>
>> Check the actual output power --
>> Connect an external wattmeter between the KPA100 and a dummy load then set
>> the K2 power knob to about 30 watts.  set to CW and hold the key down long
>> enough to read the external wattmeter.  If it shows full power output
>> (greater than 100 watts), you have a problem with the wattmeter in the KPA100
>> - most likely bad diodes at D16 and D17.
>>
>> 73,
>> Don W3FPR
>>
>>
>> On 4/2/2012 11:37 AM, Hisashi T Fujinaka wrote:
>>> OK, it's S/N 4355 with all the latest mods and it used to just reset
>>> when I got on 15M phone. Now it's resetting on 30M CW while I'm trying
>>> to work DX so it's bugging me. :)
>>>
>>> Besides the standard checking for 10-year-old cold solder joints, is
>>> there anything else to check right away?
>>>