18 March 2012

2000+miles in a week

Hello Worldwide audience of 4!

I had a rather busy week of driving. This is a necessary part of my life anyway, as the roving Sales Engineer for the east coast of England and all of Scotland. Planting myself in my Skoda VRS and engaging cruise control (NO not missiles... I don’t know... you people!) and listening to Radio-4 (valium for the ears) time just flies by, as I drive on auto-pilot. When young and foolish I thought belting along as fast as I could was the fun and exciting thing to do. Then I grew up and realised what a complete twerp I had been, risking life and limb to save a few seconds, or (gasp) possibly whole minutes! Thank god I grew up, I probably improved road safety for everyone else by an order of magnitude!

James was joining the British Army and had to be down at Pirbright by 1030 hours. I made that automatically to ‘be there at 1000 hours’, and Google Maps suggested 3.5 hours to drive from Ellesmere Port (James lives with girlfriend and her young son for whom James is a good father figure). I drove over from York the night before, ready for a 0430 wake-up and a 0500 hours start. Allowing lots of time for bio-breaks, etc... So that was 90 miles already, from York. Another 235 to get to Pirbright. James was whisked off and not seen again, while the rest of us walked around on the guided tour to see where the young new recruits would be for the next 12 weeks. Mind you, James is 28 so by far the oldest of the ‘new’ lot. He probably has a good 10 to 11 years on the ones I saw. Was I EVER that young? 235 miles back and hours of delay with blocked motorways... then back to York and home in time to curse my stiff back after more than 10 hours of sitting down without real movement.

My damned office had booked me out and about after my ‘holiday’ of helping the British Army with my youngest son. I had asked them to let me be at home planning my next week and finishing some quotes, but... no... out you go. Up to a limestone quarry miles away in Derbyshire and right on top of the Pennines. From then on throughout the week it was high mileage every day. I just died on Friday night and fell into an aching and weary sleep.

5x TCs on my desk and I have 4x of them in the process just now. I have just discovered (re-discovered) that using a method devised years ago at Intel Corporation (Swindon) UK Ltd, is good for seemingly unrepairable TC boards, that develop a short circuit on their 5V supply lines.

Think this through... if the 5V supply is a short circuit, what is causing it? All the chips and components are surface mounted and tiny. The PCB is multi-layered and nothing seems broken or burnt. A short circuit will simply make the switching power supply unit turn itself off. A bit of a whistle and it safely shuts down. These TCs are usually the Mark3 versions that have DELTA PSU lurking inside. The PSU does not die but something on the board does, effectively killing it. The answer is good old-fashioned brute force! No no, not the Naysmyth and Wilson steam hammer (that’s for the baseplate holes... :-) ) I used a 6V lead-acid battery, tiny thing really and fully sealed, somewhat smaller than a Rubik’s Cube. Strip the board of everything that can be unplugged and send 6V down the 5V supply socket. The battery has a current limit of about 120 Amps when short circuited. A brief spark and a slight whiff of smoke from a tiny ceramic capacitor as it heated itself to an early grave... the all the lights on the board came on! It was booting up!

A quick rebuild and all seems well. The fault is no more and the board, now running cool with the fan mod, seems to be performing well. I will send this back to the brave customer who gave me the go-ahead to try out what could have been completely terminal. Thinking it through however, it was a calculated overcurrent and only on the fault.

I’ll report what he reports...