[Elecraft] KPA-100 QRP except on 80m

[Bob Towers]

I've just completed building the kit (bought 3 months ago from Elecraft) 
and all went well until I got to Page 50 of the manual, the QRO transmit 
tests. I could only get any power above 11 watts on 80m (I don't have 
the 160m module). On all the other bands the output power to the dummy 
load, measured on my power/SWR meter, got to 10-11 watts when K1/K2 
tripped and then dropped to a few watts and would not increase at all. 
On all bands the SWR into the dummy load was 1.1:1 or better.

I thought at first it might be the LPFs, but now I think it isn't

a) receive performance was the same across all bands
b) QRP maximum output was 9-12 watts on all bands
c) the KPA-100 relays tripped at the appropriate band changes eg 17/2 -> 
10/12/15 -> 80.
d) the toroids in the LPFs were all soldered in right
e) the physical layout of the LPFs (toroids, capacitor values) is right.

I did a few voltage measurements:

                                   	Bands         QRP (<11W) 
QRO (>=11W)

T sense (pin 5 of U1)                80            0.00V              0.62V
   					all other        0.00V              0.00V


For some reason, the power amp isn't switching on, on all bands except 
80m. Presumably T sense is the trigger...

Any help would be much appreciated.

Many thanks

Bob Towers
MM0RKT