[Elecraft] KPA/100 displays wrong PS current (much lower)

[Ioannis Kassotakis]

Thanks Don,
That means that at HI PWR (>11 Watts) should disregard the displayed PS
current figures.
I thought that KPA100 processor would communicate the I Sense back to the
MCU and display the correct current figure after rescaling. I understand
that is not the case.

73,

Ioannis PA1EQP

On Sunday, 24 April 2016, Don Wilhelm <donwilh at embarqmail.com> wrote:

> Ioannis,
>
> The current display on the K2 indicates only the current for the base K2,
> not for the K2 and KPA100 combination.
> That is why you set the CAL CUR to 3.50 amps even though the KPA100 will
> draw much more current.
>
> Yes, the KPA100 does have a scaling on the amount of RF voltage that is
> being detected.  That is used for power control and has nothing to do with
> the current displayed.  The result of that voltage is sent to the VRFDET
> signal in the K2 (Voltage of the RF Detected).
>
> 73,
> Don W3FPR
>
> On 4/24/2016 12:05 PM, Ioannis Kassotakis wrote:
>
>> Just finished building the KPA-100 for my S/N 2102 K2 (MCU v. 2.03D, KPA
>> 1.06)
>> The K2/100 does not display the correct 13.8 V power supply current (by
>> taping Display) when it switches to HI POWER (>10 Watts).
>> I used a DMM in series to accurately measure the PS supplied current while
>> checking the K2 display at several power settings . Later, I also measured
>> the KPA TP1 voltage which is the I sense input to the KPA-100 processor.
>> For several power settings I got:
>> PWR (Watts) - PS Current (DMM) Amps - K2 Current Display Amps - KPA/100
>> TP1
>> (mV)
>> RX-0.4 - 0.44 - 0 <x-apple-data-detectors://0>
>> 1.0- 1.72- 1.76 -0
>> 5.0 - 3.3-3.3 - 0
>> 10- 3.8 - 3.8 - 0
>> 15- 4.5 - 1.01 - Not measured
>> 20- 5.4 - 1.02 - 100
>> 40 - 7.0 - 1.20 - 250
>> 60 - 8.5 - 1.28 -380
>> 80 - 9.5 - 1.41 - 500
>> 100 - 10.3 - 1.48 - 580
>> 111 - 10.8 - 1.54 - N/A
>> The measurements were done at 40 m (7.100) at CW to a dummy load through
>> KAT-100.
>>
>> It seems to work fine a LO PWR (<11 Watts) but appears to have a scaling
>> issue, when the PA switches On to HI PWR mode.
>> According to the schem (p.61) I Sense is supposed to vary 0-5 V for 0-32
>> A,
>> so the TP1 figures seem to be rather low.
>> Is this a known issue? Is it possible that I have a failed U7 or Q5 ?
>>
>>
>>
>

-- 
Ioannis Kassotakis