Super-obscure SI tech problem (solution)
Alex Yeckley
Normally I use water-soluable flux for my repair work, but
I figured I'd give no-clean flux a try (don't have to hit the
board with compressed air - saves time). I've been using
it for a couple months, and I'm pretty happy with it.
Then tonight I'm working on a Space Invaders sound problem
(no base explosion sound). Replaced the LM3900, no joy.
Checked every component - still no problem. Re-check
the in-circuit resistance of a 2.2M resistor. Hmmm, only
1.1M. OK, compare that to a known-good board - hey,
that one's reading 2.2M in-circuit. Yada, yada, yada,
pull the socket back off and remove all the components,
I have 1.1M across two unpopulated pads! Turns out the
no-clean flux was conducting too much. Absolutely no
solder involved here, just the no-clean residue! Sand it
off, put in a new socket using water-soluable, and it works
OK. Three hours of my life I'll never get back.
No wonder so many SI's develop sound problems within
a few weeks of repair! Hyper-hyper-sensitive-crappy
design. Just had to share...