[Elecraft] [K2] K2/100 lost power control

[Don Wilhelm]

  David,

That symptom is caused by the output power not being communicated back 
to the base K2 microprocessor.
The normal reason is diodes D16 and D17, but there are other reasons as 
well.  U6 is another probable failure point.

To take some stress off things in the KPA100, power the base K2 through 
the coaxial power jack (antenna still connects to the KPA100) and do not 
apply power to the KPA100.  First check is to see if you still have no 
power control - set the power request at 3 to 5 watts and do a TUNE 
(into a dummy load of course!)  If you get substantially more than the 
power requested, you confirmed the problem is in the wattmeter and its 
output circuits.

If you can follow the schematic path for the D16 output through U5 and 
U6 to the RFDET signal line you should do that - the voltages are DC, so 
it is easy to measure with your DMM.  Remember that the base K2 PA 
transistors are likely being pumped to the max while you are 
troubleshooting, so keep the transmit (or TUNE) times short.

If you have trouble following the path, send me a private note and I can 
help you with the measurements.

73,
Don W3FPR


On 6/11/2011 8:20 AM, aj4tf wrote:
> I have lost power control on K2/100.   RF output goes to full power no
> matter what the setting.
>
> I checked D16/D17 on the KPA100 and they seem to be OK.   I'll search the
> mailing list for some other things to check, but any ideas would be
> appreciated.
>
> david de AJ4TF
>