System/1 Build Log
An ongoing chronology of System/1's construction, and any other related musings.
17th January, 2015 - Adventures in the removal of flux residue
Having completed construction of the memory interface board before Christmas, I sat down earlier in the month to populate it with chips and make sure it behaved as expected. Alas I quickly noticed that the flux residue on the board made this rather unpleasant; although it had dried enough to no longer be sticky when handled, it had coated the board and sockets to such an extent that I wasn't confident some of the pressed-pin sockets would make particularly good contact — they looked rather gunked up. In fact, the entire board looked a bit mucky under good light!
On the less densely-populated boards I've built for the project so far I'd got into the habit of cleaning flux residue off with suitable solvents and an old toothbrush; this is a procedure not without its risks, as I'm pretty sure the scrubbing with the brush was the reason one of the wires on the flags register board snapped, for instance. I didn't want to risk disturbing anything on the memory interface, as it's far more densely connected than any previous efforts and could easily end up a nightmare to fix if several connections broke — but I wasn't particularly keen to leave it covered in muck, either. So after a look on eBay and a bit of deliberation, I ordered an ultrasonic cleaner with a large enough tank and basket to accomodate assembled Eurocards.
It took a week longer to arrive than anticipated (the joys of drop shipping!), but it finally arrived on Thursday and looked to be a pretty impressive unit for the money. (It certainly doesn't hurt to have a manual that's been properly translated into English, rather than the usual nearly-incomprehensible efforts on such low-budget Chinese imports...)
Rather than risk the memory interface board itself on a test run through the cleaner, over the last week I've built a RAM board which should be somewhat easier to repair or rebuild should it be damaged by my efforts; it will also allow me to do a full functional test of the memory interface instead of just characterising the bus signals. An initial attempt at cleaning it in just the supplied concentrated cleaning solution only made a slight improvement — in fact, my fingerprint was still visible in one patch of residue — but after squirting the board with some flux cleaning solvent to loosen it up before putting it back in the tank, the second attempt went much better. The RAM board survived the experience (according to a quick continuity check) so the memory interface board soon received the same treatment. Onwards and upwards!