After a thorough inspection, the problem seemed to be that two PA transistors had blown and so using Don Wilhelm's advice to purchase the K2PAKIT from Elecraft - (that kit has matched PA transistors plus replacements for Q11 and Q13 both PA2222a), I set to work removing the suspect parts.
Q11 and one of the PA transistors had definitely blown big style and no wonder there was a bang from rig when I tried to transmit. I couldn't see any other issue and I would double check when putting everything back together a by simple series of voltage tests.
Q11 blown to smithereens!
The blown PA Transistor (the one on the right!)
After a good clean up I carefully read Don's excellent instructions.
"Install Q11 and Q13 first, then check the voltage at the base solder pads for Q7 and Q8. It must be zero during receive. Then do a TUNE and measure the PA transistor base solder pad voltage. If it is not in the range of 0.60 to 0.64 volts, investigate the resistors in the Q11/Q13 circuit. Only after those checks should you install Q7 and Q8. That should get the base K2 working".
The K2PAKIT finally arrived from Elecraft and I could begin the repair. Removing the old parts proved difficult to say the least, patients and a steady hand is required using the copper flex to remove the old solder. I used an old needle to make sure the holes in the circuit board were back to their correct size, (a little tip I picked a long time ago!) finally without damaging the circuit board I managed to remove all suspect parts. Replacing them was just a case of referring from the manual to make sure everything was correctly placed.
You can see where the PA transistors should go right in the centre of the picture, 3 holes in a row,
Unfortunately one of the smaller transistors (Q13) got damaged so I had to replace, which took another few days to order. But finally with much perseverance I got there in the end and after reading up in the manual and following Don's instructions to the letter, everything fitted back together. A quick test with a multi meter all looked good and I switched on, it was working perfectly.
I'm going to keep it as a QRP without the 100 watts, I hardly ever used more than 10 watts anyway so I might as well keep it as the original QRP Rig!