[Elecraft] K2 KPA100 SWR Bridge Readings Way Too High

[Don Wilhelm]

Dick,

That is mystifying.   With the diode "backwards", you get a positive 
voltage at U5 pin 3 - that should be the correct orientation for D17.

For the power indication, check the polarity of the voltage at U5 pin 5 
- if that is negative, then D16 is also backwards.

You may have a situation where T4 is not wound with the correct sense, 
although the orientation of the diodes should still produce a positive 
voltage at U5.
Something is strange here.

73,
Don W3FPR

On 10/3/2017 3:44 PM, Dick Lamb wrote:
> 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 
> <mailto: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.
>