[Elecraft] K2/100

[W3FPR]

Andrew,

One way to check check for continuity between the KPA100 VRFDET signal 
and the base K2 is to check the voltage at KPA100 U6 pin 6 and The base 
K2 Control board U6 pin 2 - they should be the same.
If not there is a broken wire connection or U6 (MCU) has a problem 
(failure).

If U6 has a failure at pin 2, you will have power problems with the base 
K2 (no KPA100 installed) as well - no proper power control.

73,
Don W3FPR

On 7/27/2026 5:38 PM, Andrew Lenton wrote:
> See comments on brackets
> KR
>
> Andrew
>
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> On July 27, 2026, at 20:11, W3FPR <w3fpr111 at gmail.com> wrote:
>
>
>> Andrew,
>>
>> With the KPA100 installed, and the power set to 10 or 11 watts, what is
>> the actual power output in TUNE?
>> It should be near 2 watts. (True this is fine.)
>>
>> If not, there is a problem in the VRFDET section of the KPA100 or in the
>> base K2.
>> First, remove the KPA100 (physically) and try it with just the base 
>> K2. (Works fine)
>>
>> If the base K2 is OK, then yoou have some KPA100 problem to solve.  Put
>> the KPA100 upside down on a box or book about 1/2 the height of the K2
>> and remove the shield. ( All done works fine)
>>
>> set the power to about 50 watts and prepare to do some voltage 
>> measurements. ( 50 Watts set up)
>>
>> (I will do this)
>>
>> Measure the voltage at U5 pin 5 - then at 5 pin 7, they should be close
>> to the same voltage.
>> U6 pin 3 should be about 1/2 that voltage.  If not, the problem is Q10
>>
>> ( Only see the problem after I put the PA back on the K2)
>>
>>
>> and possibly Q11.
>>
>> If all OK this far, then make certain U6 pin 8 is near 5 volts.
>> If so, then check U6 pin 6 and tell me what the voltage there actually
>> is.  U6 is a common failure.
>>
>> 73,
>> Don W3FPR
>>
>> On 7/26/2026 1:16 PM, Andrew Lenton via Elecraft wrote:
>>> Hi I have just performed all the mods on the KPA100 and reset the FWD
>>> and REF and set the bias at 400mA, my bird watt meter tracks the
>>> indicated power on the K2
>>>   After fitting the screen and putting it all back together it works
>>> fine on SSB.
>>>   On low power tune is fine, however on more than 11 Watts pressing
>>> tune causes the power to jump to 140 and the SWR 2.2:1, so suspecting
>>> it is "hooting" when all back together.
>>>
>>>  Before I dive in an suggestions?