Sunday, January 1, 2017

How to Blow Up Your K2 in One Easy Lesson!

OK, my own dumb fault, Friday morning playing with the K2 just getting some QRP work done and I had come off the air with German station feeling quite pleased with myself. I decided to  listen to a  different frequency 18Mhz on the FT 9000MP to see if the newly built Moxon would pick any thing up at a height of about 15 feet.

Forgetting completely about the K2 still being on, I hear a Russian station on 18Mhz via the FT 9000 and think blimey the Moxon is working even at that height! I decide to reply, so tune the FT for 40 watts and hit the CW key.

BANG goes the K2! First reaction Jesus I've blown it up! Panicking I quickly carry out some checks, Switch off, this particular rig is fitted with K2/100 (100 watt kit), so I'm really worried I've damaged that particular option. I switch back on, I can still receive OK, all bands OK, transmit tone is still there but no transmit output, what have I blown?

I start to take the K2 apart trying desperately to remember how its all put together, the manuals come out and I start reading thinking did I really build this radio, it's so complicated, I remove the K2/100, get the top cover off then the sides and finally the underneath, back to the bare bones and then start with the magnifying glass and some bright lighting, looking for anything obvious.

Eventually after combing through various circuit boards I find a PA transistor (Q11) on the main circuit board had been completed shattered, this after finding it remains at the very bottom of the radio. Checking all other PA transistor there's nothing obvious. I check elsewhere, I couldn't find any damage with the K2/100, so fingers crossed, this is the only messed up bit.

No wonder there was a loud bang! 

I contacted the Elecraft  forum and was soon in chat with Don Wilhelm who suggested I get the K2PAKIT which has the PA transistors and also replace two diodes as a precaution in case I've blown something else. He instructs me what I need to check and possibly change.

I've put the radio back together and rebuilt as a the standard transceiver without the K2/100 (I only used about 10 watts maximum anyway) and am awaiting the parts from Elecraft, hopefully it's a small bit of damage and that's it, the cost is around 20 odd dollars, but combined international and import postal duties push it up to nearly $60 so it's a lesson well learned.

There will be more info on the repair when the parts arrive, but just imagine if I had decided to transmit the Ft9000 on 2 or 300 watts instead of just 40, god knows what would have happened to the K2!

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