[Elecraft] K2 Low transmit power after shut down

[Mick Hall]

Hi

Working on my K2 with a long wire antenna and externalATU and my K2 shut down. Only working at 5 watts and an SWR of 2.1:1.


 
I didn’t smell anything initially so I powered it backup. At first I couldn’t hear anything on any band and slowly the sound cameback, which was a bit strange.


 
The lights on the ATU no longer indicated any output sostarted checking a bit more when I got a faint smell of fried component. 


 
Before removing any covers I started checking basicthings. S meter stopped registering any received signals, although all bandscould be heard at normal levels.


 
The ATU can only handle 15 watts so I tested up to thisand found that when I dialled in up to 10 watts, It was indicating 0.5 watts. Icould hear the KPA100 switch in at 11 watts but anything up to 15 watts showeda max of 6 watts.


 
I bypassed the KPA100 by powering it from the base K2power socket and the I had the same results. 


 
I immediately thought that the finals have blown but whythe S meter issue?


 
Here are some voltages as I worked through the transmittersignal tracing.


 
P13 Basic voltagechecks 

step 4.

Key down volts at D6 2.6v and D7 7.9v

step 5.

Power output  0.5W


 
Page 14 Tx mixer,Buffer, Band Pass etc.

Step2

Xmit Mixer Output 2.12vrms

Step 3

Buffer Output 1.61vrms

Step 4

BP filter output 5.65vrms

Step5

T-R switch #1 output 5.6vrms


 
Pre-driver, Driverand PA

Step1

Pre-driver output 4vrms

Step2

Driver Input 1.26rms

Step3

Driver Output 8.2vrms

Step 4

PA input Q7 1.77vrms

Step5

PA input Q8 3.56vrms

Step 6

RF detector input .38vrms

Step 7

DMM set to Diode mode

Q7          Base1.125

                Collector1.12

                Emitter0

                

Q8          B 1.12

                C1.12

                E 0


 
Something else I noticed was that when I turn the RF gaindown fully then back up to max, the sound comes back slowly and not at the samerate you turn the dial, there is a lag.

These last results I think indicate the finals, but whereto start looking for the cause?

Any help would be much appreciated.


 
Mick