Saturday, April 04, 2009

Megajolt assembled

The latest version of Megajolt Light Jr (version 4) is a tricky little bugger to assemble if, like me, your soldering skills are infrequently tested. Most of the components are surface-mounted, which makes assembly far less of a D-I-Y proposition than previous incarnations. I tried, realised it's harder than it looks and gave up before damaging anything. Luckily, my brother Tim is an electronics genius (I knew this before I ordered the kit, of course) so I gave it to him. Here's what he emailed me today:

"Hi Nick,
"Almost had it complete on Thursday evening, and had it all done yesterday afternoon, done the basic tests, voltages all correct and on correct points. Reworked your solder joints, you really need a very fine tipped iron for SMD stuff, needle tipped less than 1mm diameter at point, and I use 0.6mm diameter solder, to ensure I get an appropriate amount, and even then I often still suck and reflow the joint. I've secured the Map sensor with two M3 stainless bolts cut to appropriate length, and I used a compound to prevent the nut from coming undone, rather than use a plastic cable tie, as the diagrams seemed to suggest, which may give way or not prevent vibration, and failure of the 6 brass legs or solder joints.

'I have also replaced the leaded filter cap (electrolytic) with an SMD tantalum, like the one on the output of the 5V regulator, I did this because the electrolytic caps, especially 85 deg rated devices do dry out, or leak, and thus are more prone to failure down the track, especially in a vehicle, where the temperature can become very high during summer, and in winter drop very low. Where possible, and we have them in stock, when replacing caps in radios, we fit the SMD tantalum types for improved reliability in the longer term. Standard electrolytic caps would be rated for say a 5 year life at 50 deg C, this will decrease with increasing temperature."

I'd say I owe the lad a curry and lager for that one!

Oh, my chassis is back from the sandblaster and half painted. When it's finished I'll post a few pictures. And start trying to remove POR-15 from my hands ;-)


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