Fwd: Re: K2/100 pwr out control problem

[RobertG]

-------- Original Message --------
Subject: Re: [Elecraft] K2/100 pwr out control problem
Date: Fri, 22 Apr 2011 20:33:40 +0000
From: Robert G. Strickland <[hidden email]>
To: [hidden email]

Hello, Don and others..

Thanks for everyone's  suggestions. Much appeciated. The problem
persists regardless of using an antenna or a dummy load. I carried out
Don's suggestions as described below.

I don't have a watt meter, so I used the RF probe on a 50ohm resistive
load and calculated the Vrms for the various power levels. Calculated
and observed readings are as follows:

        Power Vrms [cal] Vrms [observed]
        10w 22.36v 18.0v
          5w 15.8v 18.0v
          2w 10.0v 18.0v

Computed power out at 18.0Vrms is 6.48w

In addition, I notice the following LCD readings at all three power
levels: the moment the TUNE button is pressed a HI CUR reading appears
that immediately changes to a power out reading is 2.1w and an SWR
reading 9.9:1. Again these reading occur at all three power settings.

Don, I'm going to assume that your first suggestion to change D16 and
D17 still holds. Yes?

...robert

On 4/22/2011 15:47, Don Wilhelm wrote:

> Robert,
>
> Make the following setup and check into a dummy load with an external
> wattmeter between the K2 and the dummy load. Please follow the testing
> method given, there is a reason for that test methodology.
> 1) Remove the APP power cord from the KPA100 and power the K2 only from
> the coaxial power jack on the lower rear panel. Set the K2 to 40 meters.
> 2) Set the power requested knob to 5 watts and press TUNE - what is the
> power on the external meter?
> 3) Set the power to 2 watts and again press TUNE - what is the power on
> the external meter?
>
> If the actual power was 10 watts or more in both cases above, change
> diodes D16 and D17 in the KPA100.
> If the actual power tracked the requested power, then you have a
> different problem - power the KPA100 from the APP power cable and try
> again into a dummy load (not an antenna). Set the power requested to 50
> watts and do a TUNE - the actual power should be near 20 watts. If it
> goes to a large value, then we need to investigate your KPA100 - remove
> it from the base K2 and take the shield off, and let us know the status
> of your results.
>
> 73,
> Don W3FPR
>
> On 4/22/2011 10:46 AM, Robert G. Strickland wrote:
>> I'm running a K2/100 Ser# 5957, operational for about three years. Just
>> now, control of pwr out has become intermittant. I can control pwr out
>> in the basic K2 thru the range 0 -13w. Anything over that and the K2
>> meter sticks at about 13w, but the amp output jumps immediately and
>> somewhat randomly to between 50-100w with no "smooth" control.
>> Decreasing the K2 pwr out below 10w or so, and the overall pwr out drops
>> accordingly, the K2 meter reads "correctly," and the total unit pwr out
>> (external meter) agrees with the K2 meter. I've tried cycling on/off,
>> different bands, different modes. All the same. Any suggestions most
>> welcome.
>>
>> ...robert
>>
>

--
Robert G. Strickland, PhD, ABPH - KE2WY
[hidden email]
Syracuse, New York, USA
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[Don Wilhelm-4]

  Robert,

Well, I am not so sure now - so the answer is "Maybe".

Completely remove the KPA100 and its cables, connect the dummy load to
the BNC antenna jack and repeat the test.  I would predict that you now
have power control (you will see something other than 18 volts RMS
across the dummy load).  If indeed that is true, then yes, KPA100 diodes
D16 and D17 need to be replaced.

Also, if during your base K2 only tests, you find that you cannot get
the actual power up to 10 watts or more, you have a base K2 power
problem too.  The most likely cause is that one of the PA transistors
was smoked because of the heavy load placed on them trying to get the
power level increased.

73,
Don W3FPR

On 4/22/2011 4:42 PM, Robert G. Strickland wrote:

>
> -------- Original Message --------
> Subject: Re: [Elecraft] K2/100 pwr out control problem
> Date: Fri, 22 Apr 2011 20:33:40 +0000
> From: Robert G. Strickland<[hidden email]>
> To: [hidden email]
>
> Hello, Don and others..
>
> Thanks for everyone's  suggestions. Much appeciated. The problem
> persists regardless of using an antenna or a dummy load. I carried out
> Don's suggestions as described below.
>
> I don't have a watt meter, so I used the RF probe on a 50ohm resistive
> load and calculated the Vrms for the various power levels. Calculated
> and observed readings are as follows:
>
> Power Vrms [cal] Vrms [observed]
> 10w 22.36v 18.0v
>  5w 15.8v 18.0v
>  2w 10.0v 18.0v
>
> Computed power out at 18.0Vrms is 6.48w
>
> In addition, I notice the following LCD readings at all three power
> levels: the moment the TUNE button is pressed a HI CUR reading appears
> that immediately changes to a power out reading is 2.1w and an SWR
> reading 9.9:1. Again these reading occur at all three power settings.
>
> Don, I'm going to assume that your first suggestion to change D16 and
> D17 still holds. Yes?
>
> ...robert
>
> On 4/22/2011 15:47, Don Wilhelm wrote:
>> Robert,
>>
>> Make the following setup and check into a dummy load with an external
>> wattmeter between the K2 and the dummy load. Please follow the testing
>> method given, there is a reason for that test methodology.
>> 1) Remove the APP power cord from the KPA100 and power the K2 only from
>> the coaxial power jack on the lower rear panel. Set the K2 to 40 meters.
>> 2) Set the power requested knob to 5 watts and press TUNE - what is the
>> power on the external meter?
>> 3) Set the power to 2 watts and again press TUNE - what is the power on
>> the external meter?
>>
>> If the actual power was 10 watts or more in both cases above, change
>> diodes D16 and D17 in the KPA100.
>> If the actual power tracked the requested power, then you have a
>> different problem - power the KPA100 from the APP power cable and try
>> again into a dummy load (not an antenna). Set the power requested to 50
>> watts and do a TUNE - the actual power should be near 20 watts. If it
>> goes to a large value, then we need to investigate your KPA100 - remove
>> it from the base K2 and take the shield off, and let us know the status
>> of your results.
>>
>> 73,
>> Don W3FPR
>>
>> On 4/22/2011 10:46 AM, Robert G. Strickland wrote:
>>> I'm running a K2/100 Ser# 5957, operational for about three years. Just
>>> now, control of pwr out has become intermittant. I can control pwr out
>>> in the basic K2 thru the range 0 -13w. Anything over that and the K2
>>> meter sticks at about 13w, but the amp output jumps immediately and
>>> somewhat randomly to between 50-100w with no "smooth" control.
>>> Decreasing the K2 pwr out below 10w or so, and the overall pwr out drops
>>> accordingly, the K2 meter reads "correctly," and the total unit pwr out
>>> (external meter) agrees with the K2 meter. I've tried cycling on/off,
>>> different bands, different modes. All the same. Any suggestions most
>>> welcome.
>>>
>>> ...robert
>>>

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