[Elecraft] bad TX IMD3 from K3S, now almost no TX output

[Andy D. Hansen]

Hi All

 

Email support from Elecraft is very slow since about the beginning of 2019. 

May be due to a system change. Before it was really good! 

I own equipment ( 3xK3S, 3xP3, 1xKPA500 etc.) 

 

Therefore I turn to this group to be able to fix my K3S TX by myself.

Sending the unit for repair to Italy is no option because of crazy VAT there
( HB9 no EU).

 

How is your equipment operating ? 

 

K3S # 10490 factory assembled is now not TX working at all, based on IMD 3
(24dB, basically on all bands) and too low output problems.  

I try to troubleshoot/repair it and need further supporting technical info.

I took out the 100W PA , replaced it with an older K3 module I had -> no
improvement.

If only running the 10W module the IMD is bad and I have only limited
output.

Analyzing the output from XVERT out BNC the signal is clean and about
1mW/50Ohm.

 

1) It would be helpful among others to receive info on the DC voltages (
Bias etc.)  in the 10 and 100W module.

In order to analyze the bias voltage/ current technical info is needed. 

 

2) Is there any good way to check the QSK diodes?

I want to make sure the diodes are working well. Should I replace them?

 

 

I did measure it at XVTR OUT BNC. Output level about -1dBm to 0dBm into 50
ohms. 

Turning on the 2 Tone (Tech MD on ) and watching on the spectrum analyzer HP
8591E ( all functions auto/ cal. ok) with 10 dB 50 Ohm external attenuator
shows a

signal (2 Tone) which looks very clean down to at least  45 dB to almost
50dB on each side. Basically there is no difference on 160 or 80m or 40 . 

I can however not see expected side products (IMD3) here. May be the signal
is just very good here ( Span e.g. 10kHz, sweep 10 sec) .

In all measurements the LPA was set to about 11 watts connected to 50 Ohm DL
anyway-probably disabled by SW . After resetting KXV3B to normal IMD3 at  PL
output -no 100W engaged - very bad again with about 10dB worst case.

 

My conclusion there is again a problem in the new LPA (10W).

What is your analysis?

When I happily replaced the 10W/100W module last year (based on returned old
once later , nice service!) all looked fine and then back to same problem. 

 

Thanks for any hints from the group .

 

 

Cu, vy 73 Andy

HB9CVQ, DK2VQ, AK4IG

 

 <https://www.qrz.com/db/HB9CVQ> https://www.qrz.com/db/HB9CVQ