Elecraft

Strange KPA100 behavior

Classic

List

Threaded

6 messages Options

Mike Geddes

Strange KPA100 behavior

Greetings. I recently finished my K2 KPA100 kit. It seemed to work okay
initially, then last night started to exhibit some strange behavior. It
would transmit correct power on tune under 11 watts (and show low SWR), but
on anything over 11 watts, on tune, it would transmit around 165 watts and
show an SWR of around 7:1!! And giving High Current message Is there
anything I should start looking for initially?

Any suggestions are appreciated.

Thanks,
Mike
N4JX

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Don Wilhelm-3

Re: Strange KPA100 behavior

Mike,

Is the K2 displaying 165 watts? Or is the K2 displaying 0.2 watts or
lower while an external wattmeter is displaying 165 watts?
What is your test setup that gives you a 7:1 SWR? If you are feeding a
resistive 50 ohm dummy load with good coax, the wattmeter (either
internal or external) should read 1:1 even with a KPA100 problem.

Tell us more so we can help with your problem -
Taking a very wild guess, you either have a non-functioning wattmeter in
the KPA100, or the KPA100 wattmeter is not calibrated, or you have a
parasitic oscillation in the KPA100.

Since this is a new kit - do you have blue toroid cores at L16 and RFC1
or do you have red toroids at L15 and L16? And tell us what the value
of C31 is and whether you determined the value by looking at the
capacitor (preferred) or whether you just looked at the parts
list/schematic.

We need the answers to all these questions before we can advise you further.

73,
Don W3FPR

Mike Geddes wrote:

> Greetings. I recently finished my K2 KPA100 kit. It seemed to work okay
> initially, then last night started to exhibit some strange behavior. It
> would transmit correct power on tune under 11 watts (and show low SWR),
> but on anything over 11 watts, on tune, it would transmit around 165
> watts and show an SWR of around 7:1!! And giving High Current message
> Is there anything I should start looking for initially?
>
> Any suggestions are appreciated.
>
> Thanks,
> Mike
> N4JX

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Mike Geddes

Re: Strange KPA100 behavior

Don,

I am not at home right now to look at K2, but will try and answer your
questions to provide additional information.

I am not sure what the K2 was displaying in terms of watts out (I
think it was a low number), but I confirmed the output at 165w using
two external wattmeters (first the Elecraft W1, which I did not
totally believe because it was maxed out, then my Bird 43 with 1000w
slug). I was connected to a Bird 125w dummy load, confirmed 50 ohm.
The cable was probably not the best, it was a 20 ft run of RG-58 I
think.

My kit used the red toroids, and I assume at L15 and L16 but would
have to check when I can look at the kit (when I get home). Also will
have to check the value of C31.

Don't know if this will help you or not . . but this is what I can
provide for now. Will check the rest when I get home this evening.

Thanks,

Mike
N4JX

----- Original Message -----
From: Don Wilhelm <[hidden email]>
Date: Monday, June 11, 2007 8:57 am
Subject: Re: [Elecraft] Strange KPA100 behavior
To: Mike Geddes <[hidden email]>
Cc: Elecraft <[hidden email]>

> Mike,
>
> Is the K2 displaying 165 watts? Or is the K2 displaying 0.2 watts
> or
> lower while an external wattmeter is displaying 165 watts?
> What is your test setup that gives you a 7:1 SWR? If you are
> feeding a
> resistive 50 ohm dummy load with good coax, the wattmeter (either
> internal or external) should read 1:1 even with a KPA100 problem.
>
> Tell us more so we can help with your problem -
> Taking a very wild guess, you either have a non-functioning
> wattmeter in
> the KPA100, or the KPA100 wattmeter is not calibrated, or you have
> a
> parasitic oscillation in the KPA100.
>
> Since this is a new kit - do you have blue toroid cores at L16 and
> RFC1
> or do you have red toroids at L15 and L16? And tell us what the
> value
> of C31 is and whether you determined the value by looking at the
> capacitor (preferred) or whether you just looked at the parts
> list/schematic.
>
> We need the answers to all these questions before we can advise
> you further.
>
> 73,
> Don W3FPR
>
> Mike Geddes wrote:
> > Greetings. I recently finished my K2 KPA100 kit. It seemed to
> work okay
> > initially, then last night started to exhibit some strange
> behavior. It
> > would transmit correct power on tune under 11 watts (and show
> low SWR),
> > but on anything over 11 watts, on tune, it would transmit around
> 165
> > watts and show an SWR of around 7:1!! And giving High Current
> message
> > Is there anything I should start looking for initially?
> >
> > Any suggestions are appreciated.
> >
> > Thanks,
> > Mike
> > N4JX
>

Don Wilhelm-3

Re: Strange KPA100 behavior

Mike,

If you are certain you had the red toroid cores (not any blue ones) then
you have the older KPA100 T/R switch design - it must have been shipped
before mid-Nov 2006. You do not have to check C31 with the red toroid
KPA100.

Do check to see if the KPA100 is displaying low power - you can do that
check at low power by powering the base K2 and removing the power from
the KPA100. If the internal wattmeter is working, you will be able to
control power output and have a correct power reading if the wattmeter
is correctly calibrated. If you cannot control power output, then you
have something wrong with the wattmeter - T4 is the first suspect, check
the lead placement and check the lead tinning carefully. Be certain the
red wire goes through the toroid core center and that the bare wire you
soldered onto the SO239 jack is well soldered to the board at T4-6.

As for the 7:1 SWR you read on the Elecraft W1 - do investigate that,
and I strongly suggest that the cause can be found in either your dummy
load or in the connecting cables - use a very short coax connection to a
dummy load.

73,
Don W3FPR

[hidden email] wrote:

> Don,
>
> I am not at home right now to look at K2, but will try and answer your
> questions to provide additional information.
>
> I am not sure what the K2 was displaying in terms of watts out (I
> think it was a low number), but I confirmed the output at 165w using
> two external wattmeters (first the Elecraft W1, which I did not
> totally believe because it was maxed out, then my Bird 43 with 1000w
> slug). I was connected to a Bird 125w dummy load, confirmed 50 ohm.
> The cable was probably not the best, it was a 20 ft run of RG-58 I
> think.
>
> My kit used the red toroids, and I assume at L15 and L16 but would
> have to check when I can look at the kit (when I get home). Also will
> have to check the value of C31.
>
> Don't know if this will help you or not . . but this is what I can
> provide for now. Will check the rest when I get home this evening.
>
> Thanks,
>
> Mike
> N4JX
>

Mike Geddes

Re: Strange KPA100 behavior

In reply to this post by Don Wilhelm-3

Don,

This evening I have had a chance to look at my KPA100 again. I verified
that I am still unable to control output above 11 watts . . . . above 11
watss it is putting out 165 watts (connected to Bird 43 meter) and showing
7:1 SWR on K2 display. Below 11 watts the output seems correct. I was
incorrect in an earlier email.

I DO have blue toroids at L16 and RFC1, and L15 is empty. I did verify that
C31 is .22mF (m22J63).

I checked T4 . . . looks okay and I seem to have proper resistance between
1/3 and 2/4. And I do have continuity between 1/4.

One curious observation . . . as I was working through the check and
alignment process again, I can only get 26.5k and 27.1k out of R26 and R27,
versus the 43k recommended for C1 adjustment.

Not sure what to look at from this point? Sorry for the prior
misinformation. Any suggestions?

Thanks,

Mike
N4JX

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Mike Geddes" <[hidden email]>
Cc: "Elecraft" <[hidden email]>
Sent: Monday, June 11, 2007 8:56 AM
Subject: Re: [Elecraft] Strange KPA100 behavior

> Mike,
>
> Is the K2 displaying 165 watts? Or is the K2 displaying 0.2 watts or
> lower while an external wattmeter is displaying 165 watts?
> What is your test setup that gives you a 7:1 SWR? If you are feeding a
> resistive 50 ohm dummy load with good coax, the wattmeter (either internal
> or external) should read 1:1 even with a KPA100 problem.
>
> Tell us more so we can help with your problem -
> Taking a very wild guess, you either have a non-functioning wattmeter in
> the KPA100, or the KPA100 wattmeter is not calibrated, or you have a
> parasitic oscillation in the KPA100.
>
> Since this is a new kit - do you have blue toroid cores at L16 and RFC1 or
> do you have red toroids at L15 and L16? And tell us what the value of C31
> is and whether you determined the value by looking at the capacitor
> (preferred) or whether you just looked at the parts list/schematic.
>
> We need the answers to all these questions before we can advise you
> further.
>
> 73,
> Don W3FPR
>
> Mike Geddes wrote:
>> Greetings. I recently finished my K2 KPA100 kit. It seemed to work okay
>> initially, then last night started to exhibit some strange behavior. It
>> would transmit correct power on tune under 11 watts (and show low SWR),
>> but on anything over 11 watts, on tune, it would transmit around 165
>> watts and show an SWR of around 7:1!! And giving High Current message Is
>> there anything I should start looking for initially?
>>
>> Any suggestions are appreciated.
>>
>> Thanks,
>> Mike
>> N4JX
>

Don Wilhelm-3

Re: Strange KPA100 behavior

Mike,

Fine, and thanks for clarifying that you do have the latest level KPA100.

The fact that you have lower than expected resistances at R26 and R27
suggest that you may have something wrong with U5 (it could be damaged).

Initially, you should make the DC voltage measurements on U5 and U6 and
Q10 and Q11 (see the DC voltage chart at the end of the manual).

The prime suspects for a problem like yours are D16 and D17, T4, U5, U6
Q10 and Q11 - of course the associated resistors can be suspect too, but
are usually not a problem if it worked before. (if it has never worked,
check the resistors associated with the devices listed above (see the
schematic to identify the resistors).

Since your KPA100 is producing maximum power, I suggest that you remove
the power from the KPA100 and feed only the DC coaxial connector on the
base K2 - that will limit the power output to the QRP level (but it will
still produce maximum power from the base K2, so keep the keydown
periods short.

If the DC voltage measurements check out with no problem indication, I
can help you trace the detected voltage from R26 through to the VRFDET
signal.

73,
Don W3FPR

Mike Geddes wrote:

> Don,
>
> This evening I have had a chance to look at my KPA100 again. I verified
> that I am still unable to control output above 11 watts . . . . above
> 11 watss it is putting out 165 watts (connected to Bird 43 meter) and
> showing 7:1 SWR on K2 display. Below 11 watts the output seems correct.
> I was incorrect in an earlier email.
>
> I DO have blue toroids at L16 and RFC1, and L15 is empty. I did verify
> that C31 is .22mF (m22J63).
>
> I checked T4 . . . looks okay and I seem to have proper resistance
> between 1/3 and 2/4. And I do have continuity between 1/4.
>
> One curious observation . . . as I was working through the check and
> alignment process again, I can only get 26.5k and 27.1k out of R26 and
> R27, versus the 43k recommended for C1 adjustment.
>
> Not sure what to look at from this point? Sorry for the prior
> misinformation. Any suggestions?
>