Re:Problem with KPA 100 (no power selection possible)

[Hartmut Kluge]

Hello Don,

thanks for Your mail.

Here are my answers:

Is this a new KPA100 that has worked before or is it a new build?
My KPA 100 is just new build.

Are you able to control the power output below 5 watts with the power
control with the KPA100 attached?
Yes, I can.

Can you control power on the base K2 if you remove the KPA100?
Yes, I can.

73,
Hartmut
DL5BT
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[Gregg R. Lengling]

[Gregg R. Lengling] what you need to look at is the SWR/Power bridge circuit
in the amp.  I had a lightning hit that screwed up my amp and caused it to
always be full power and it turned out this is the circuit that caused the
problem.  The VRFDET line is used to control the output power of the unit,
it needs to be able to see if requested power = delivered power.  So you
have a problem there.  This is where you start.
[Gregg R. Lengling]

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[Don Wilhelm-3]

Hartmut,

If you can control the less than 11 watt power with the KPA100 attached,
that deepens the mystery.  It also tells me that the VRFDET signal is
working from the KPA100.

Do you have the trimmer pots R26 and R27 set near their mid-rotation
positions as they should be.
Balance the wattmeter (C1 adjustment) at low power (<11 watts), and also
initially set the R26 trimmer to match the actual power output at <11 watts
(you should refine it at higher power later when all is working right).

Can you determine the frequency of the output when the amplifier goes to
full power.  If it is not at the frequency of the input, you have an
oscillation.  If you have an oscilliscope, look for an oscillation near 600
kHz.

Check the orientation of Q6 and Q7.  If they are reversed, the KPA100 will
turn into a big oscillator.  The body on these devices has a flat on both
sides - the side with the shortest flat is the 'rounded' side on the board
silkscreen.

Be certain you have an 8.45k 1% resistor at R24 and check the soldering at
RP1, especially pins 1 and 2.

Check the soldering at R16 and R15 carefully.

Be certain Q10 conducts (drain at zero volts) during high power transmit.

What is the voltage at each end of R24 when transmitting at 9 or 10 watts?
Then what is the voltage at each end when transmitting at 50 or 100 watts?
(do not transmit for a significant length of time).

Let us know what you find.

73,
Don W3FPR

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]]On Behalf Of Hartmut Kluge
> Sent: Tuesday, February 27, 2007 4:42 PM
> To: [hidden email]
> Cc: [hidden email]
> Subject: [Elecraft] Re:Problem with KPA 100 (no power selection
> possible)
>
>
> Hello Don,
>
> thanks for Your mail.
>
> Here are my answers:
>
> Is this a new KPA100 that has worked before or is it a new build?
> My KPA 100 is just new build.
>
> Are you able to control the power output below 5 watts with the power
> control with the KPA100 attached?
> Yes, I can.
>
> Can you control power on the base K2 if you remove the KPA100?
> Yes, I can.
>
> 73,
> Hartmut
> DL5BT
>

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2:56 PM

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