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KPA100 bias issues...

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Steve Kallal

KPA100 bias issues...

I have progressed through the KPA100 adjustments with NO issues until I got
to the bias adjustments on pages 49 and 50. I am unable to get any current
reading changes when adjusting R6. First of all, my current drain at 0.1
watts is about 500 mA rather than the 200 to 400 mA mentioned in the manual.
When I go into TUNE mode and set the power to 11 watts, the current drops to
about 600 mA and there is NO current change when adjusting R6. There are two
errors that pop up on the LCD display. First it displays HI REFL and then PA
HOT. I went back and double checked my TPA and SWR settings from the
previous section. All is OK.

I welcome any suggestions or hints at this point.

73,

Steve N6VL

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Don Wilhelm-4

Re: KPA100 bias issues...

Steve,

Rotate the KPA100 bias pot back to its full counterclockwise position,
make certain you have a good dummy load on the KPA100, and then try the
steps below:

First, determine if the current draw at 0.1 watts is high in the base K2
or the KPA100.
Disconnect the ribbon cable to the KPA100 and measure the current draw -
expect 240ma to 360 ma - this will depend on how many options you have
installed - low end if you have no options and high end if your K2 has a
full house (especially the KDSP2). If you have considerably more
current draw than that, re-look at the base K2 for the cause.

If your current draw is within range, power off and install the ribbon
cable - the KPA100 will add some to the current draw found in the above
step - expect 50 to 100 ma more..

Now turn the power up to 11 watts or higher - the current should
increase another 100 to 150 ma depending on the state of the fan.

When all the above is within range, put the K2 into CW TEST - that is
very important.

Add 400 ma to whatever the current draw was in the above 11+ watt check
- that is your desired final bias current setting.

Now press TUNE - at first the current will not increase very much, but
with rotation of the bias pot, the current should increase. Find the
place where the current increases about 400 ma and stop for now - you
are close.

Go out of TUNE by tapping any button - do not power off or you will
lose the CW TEST condition
(that is why you received the HI REFL message).

Enter TUNE and quickly check the current draw and exit TUNE. The
current draw will climb after a half second or so, but the initial
reading on your DMM may be too low because the gate timing on your DMM
is not synchronized, so look at the reading for the second scan - in
other words wait more than a tenth of a second and less than half a
second to see the correct reading.

If the reading is too low adjust the pot slightly clockwise, but if it
is too high, adjust it a tiny bit in the counterclockwise direction.

73,
Don W3FPR

Steve Kallal wrote:

> I have progressed through the KPA100 adjustments with NO issues until I got
> to the bias adjustments on pages 49 and 50. I am unable to get any current
> reading changes when adjusting R6. First of all, my current drain at 0.1
> watts is about 500 mA rather than the 200 to 400 mA mentioned in the manual.
> When I go into TUNE mode and set the power to 11 watts, the current drops to
> about 600 mA and there is NO current change when adjusting R6. There are two
> errors that pop up on the LCD display. First it displays HI REFL and then PA
> HOT. I went back and double checked my TPA and SWR settings from the
> previous section. All is OK.
>
>
>

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Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
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Elecraft web page: http://www.elecraft.com

Steve Kallal

RE: KPA100 bias issues...

Don,

I found that I'd installed U7 backwards. U7 is at the heart of the bias
control. I can't find a cross reference for LMC6482 at a couple of local
parts stores. I don't know if removing it and reinstalling it will work. I
am having problems removing and it may have been damaged.

I am trying to find a cross reference on the interent and seeing if a couple
of parts stores might have it. They don't have a reference for it.

73,

Steve N6VL

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Saturday, August 11, 2007 3:06 PM
To: Steve Kallal
Cc: [hidden email]
Subject: Re: [Elecraft] KPA100 bias issues...

Steve,

Rotate the KPA100 bias pot back to its full counterclockwise position, make
certain you have a good dummy load on the KPA100, and then try the steps
below:

First, determine if the current draw at 0.1 watts is high in the base K2 or
the KPA100.
Disconnect the ribbon cable to the KPA100 and measure the current draw -
expect 240ma to 360 ma - this will depend on how many options you have
installed - low end if you have no options and high end if your K2 has a
full house (especially the KDSP2). If you have considerably more current
draw than that, re-look at the base K2 for the cause.

If your current draw is within range, power off and install the ribbon cable
- the KPA100 will add some to the current draw found in the above step -
expect 50 to 100 ma more..

Now turn the power up to 11 watts or higher - the current should increase
another 100 to 150 ma depending on the state of the fan.

When all the above is within range, put the K2 into CW TEST - that is very
important.

Add 400 ma to whatever the current draw was in the above 11+ watt check
- that is your desired final bias current setting.

Now press TUNE - at first the current will not increase very much, but with
rotation of the bias pot, the current should increase. Find the place where
the current increases about 400 ma and stop for now - you are close.

Go out of TUNE by tapping any button - do not power off or you will lose
the CW TEST condition (that is why you received the HI REFL message).

Enter TUNE and quickly check the current draw and exit TUNE. The current
draw will climb after a half second or so, but the initial reading on your
DMM may be too low because the gate timing on your DMM is not synchronized,
so look at the reading for the second scan - in other words wait more than a
tenth of a second and less than half a second to see the correct reading.

If the reading is too low adjust the pot slightly clockwise, but if it is
too high, adjust it a tiny bit in the counterclockwise direction.

73,
Don W3FPR

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Post to: [hidden email]
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Subscriber Info (Addr. Change, sub, unsub etc.):
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Don Wilhelm-4

Re: KPA100 bias issues...

Steve,

If you do not have proper removal equipment and are having ANY problems
getting it out intact - forget trying to remove it intact - clip its
leads off and remove them one leg at a time.

You may find it quicker to ask Elecraft for a replacement than waiting
for shippment from another source. A note to [hidden email] will
likely have the part on its way to you Monday.

73,
Don W3FPR

Steve Kallal wrote:

> Don,
>
> I found that I'd installed U7 backwards. U7 is at the heart of the bias
> control. I can't find a cross reference for LMC6482 at a couple of local
> parts stores. I don't know if removing it and reinstalling it will work. I
> am having problems removing and it may have been damaged.
>
> I am trying to find a cross reference on the interent and seeing if a couple
> of parts stores might have it. They don't have a reference for it.
>
>
>