[Elecraft] K2 KPA100 SWR Bridge Readings Way Too High

[Dick Lamb]

Yes, the voltage is negative on U5 Pin 3, but D17 is not installed
backward--i.e., the cathode band is on the side away from the coax
connector, as shown in the manual.  I tried reversing the diodes (cathode
band on the side of the the coax connector), and Pin 3 voltage does drop to
millivolt positive range, and the SWR shows 1:1, but the power output
doesn't change regardless of the "power" knob setting.  I verified that the
diodes are banded correctly with a semiconductor tester.    Dick, K0KK

On Tue, Oct 3, 2017 at 1:20 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:

> Dick,
>
> Is that voltage at U5 pin 3 actually negative?  If so diode D17 is
> backwards - the voltage should be positive in all cases.  Yes, C1 will not
> adjust if the D17 polatity is wrong.
> You can refer to the parts placement diagram at the back of the KPA100
> manual if you cannot see the silkscreen clearly.
>
> After putting D17 in correctly, recheck the 43k initial setting of R27 and
> go from there.
>
> 73,
> Don W3FPR
>
>
> On 10/3/2017 2:08 PM, Dick Lamb wrote:
>
>> Don,
>>
>> I set both R26 and R27 to 43K Ohms, applied power directly to the base
>> unit (no power to KPA100), and set power know to call for 10 W.  In TUNE
>> mode the SWR reads about 9.9:1 regardless of C1 setting.  I think the C1
>> setting has no effect.  I measure the power out at about 15 W, and the K2
>> says it's putting out about 5 W.  Voltage at U5 Pin 3 is about -1.040 V.
>>
>>
>>
>