K2 transmit too high

[N8CEP]

My K2 is still transmitting at 10+ watts even though it is set at a
lower level.
When transmitting the K2 says Hi-Cur and then shows a power level of 0.1
even though the wattmeter shows 10+ watts. I have checked pin 10 of the
control board P4 and it shows
0 volts when receiving and 1.2 watts when transmitting. I have checked
all the RF detection parts
and the control board parts. It seems that U6 is getting a voltage of
6.2 on transmit but nothing is
helping reducing power. I must be missing something. I have no control
over the power level. I hate to take off the heat sink until I am more
certain where to look for the problem.

Any ideas would be welcome.  73
Keith Hamilton, W8GX
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[Don Wilhelm-3]

Kieth,

OK, you seem to have VRFDET in proper order on your K2, so next step is to
check the circuits that are driven by the uP to control the power level.

To briefly explain how the power control works in the K2 - the power
requested is known to the uP, and the actual output power is indicated to
the uP through the VRFDET signal.  The uP compares these two and adjusts
VPWR up or down as required - then that signal flows through the keying
waveshape (and ALC) circuits and exits there as VALC - that resulting
voltage is applied to RF Board Q24 through R98 and Q24 in turn controls the
amount of RF voltage from the BFO is to be sent on to the Transmit Mixer.

I would start with VPWR at Control Board U8 pin 2 - I can't predict exactly
what the voltage here should be, but it should be smaller if the uP is
attempting to reduce the power output - I would expect something in the
vicinity of 0 to 1 volts (note that 5 volts will be present if the menu is
set for CAL FCTR).  If that is correct, next check VALC at the emitter of
Control Board Q8 - again I would expect something finite, but rather low
here if the output power is greater than that requested (the values in the
DC voltage chart are for the condition of CAL FCTR set in the menu).  If you
find VALC is a high voltage, the ploblem lies in the ALC circuit - look at
the schematic for the Control Board and see the ALC section at the upper
left - identify all the associated components and check them for proper
value and placement - especially check the placement of C45 and C46 which
are soldered on the bottom of the Control Board.

If you don't find the problem here, let us know and we will look elsewhere
(in the transmit chain rather than the controls - you should be prepared to
measure RF Voltages).

73,
Don W3FPR

> -----Original Message-----
>
> My K2 is still transmitting at 10+ watts even though it is set at a
> lower level.
> When transmitting the K2 says Hi-Cur and then shows a power level of 0.1
> even though the wattmeter shows 10+ watts. I have checked pin 10 of the
> control board P4 and it shows
> 0 volts when receiving and 1.2 watts when transmitting. I have checked
> all the RF detection parts
> and the control board parts. It seems that U6 is getting a voltage of
> 6.2 on transmit but nothing is
> helping reducing power. I must be missing something. I have no control
> over the power level. I hate to take off the heat sink until I am more
> certain where to look for the problem.
>
>

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