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
>
______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html
Locked
