[Elecraft] Fwd: Re: K2/100 pwr out control problem

[Robert G. Strickland]

-------- Original Message --------
Subject: Re: [Elecraft] K2/100 pwr out control problem
Date: Fri, 22 Apr 2011 21:22:17 +0000
From: Robert G. Strickland <rcrgs at verizon.net>
To: don at w3fpr.com

Don...

The base K2's power is continuously adjustable from low to over 10w as
measured by the RF probe. However, the Vrms readings don't jibe w/ the
power out as indicated on the K2 lcd. I did run the bare K2 through my
antenna tuner that has a cross needle forward/reflected meter [yes,
they're barely accurate at best] and that showed continuously variable
power from nil to quite a bit over 10w indicated.

The exact power reading at this point is indeterminate, but I'm pretty
sure that it's up there. When this problem started, I noticed it by not
being able to control the power out from the amp; it was being driven to
around 700w out [too much]. To do this would require a drive level of
around 50w from the K100 which would, in turn, require "something" from
the base K2. I'll get some diodes and report back.

Thanks.

...robert


On 4/22/2011 20:55, Don Wilhelm wrote:
> Robert,
>
> Yes, that is the first step.
>
> The K2s attempt to drive the power higher (the microprocessor thinks the
> power output is low) may have damaged one of the base K2 PA transistors,
> but replace the diodes first and then that check can be made.
>
> If you have to order the diodes from Elecraft, you may want to check on
> the health of the base PA first.
> To do that, remove the KPA100 and check the maximum power output
> available from the base K2. If you cannot get at least 10 watts out of
> it on most bands (all exxcept for possibly 10 meters), then it is likely
> the PA transistors must be replaced - order K2PAKIT from Elecraft.
>
> 73,
> Don W3FPR
>
> On 4/22/2011 4:33 PM, Robert G. Strickland wrote:
>> 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
rcrgs at verizon.net
Syracuse, New York, USA