29 Apr
2010
29 Apr
'10
8:49 a.m.
On Wednesday (04/28/2010 at 04:54PM -0700), Brent Hilpert wrote:
As it turned out, a junction-FET had developed a sensitivity to changes in the
nearby electrostatic or electromagnetic field, or to stray photons: the
"+"-polarity indicator in the display was a neon lamp located within a few
millimetres of the FET, when the lamp switched on the FET would trigger into a
latch-up state. (Accessing the unit for service moved the neon lamp a couple of
centimetres away from the FET, which explained why it didn't fail then.)
Wow. Cool and crazy frusterating :-)
So, all in the realm of speculation, but marginal or
spurious semiconductor
junctions can do funny things, like exhibiting weird latch-up behaviour.
Indeed. Once I get the SDK85 back running like it should, perhaps
I'll poke around on the 8355 a bit and see if I can't find some clues.
I don't really have tools to do any serious analysis but I can do things
like vary the supply voltage, clock rate, etc-- a number of external
things-- and see if there are any margins over which it will work again.
Chris
--
Chris Elmquist