Dave VanHorn said:
EVERYONE caught that one, but the can itself was insulated from the rest of
the cap, in every case that we checked. However, the large capacitance
between the can and the cap terminals (large if you're turning on and off at
300kHz) didn't show up on an ohmmeter. It did make the converter run much
slower, saturating the inductor, and eventually flaming out in a pretty
spectacular way.
nice. I've had to redesign a fair few saturating inductors, too, including a
flyback transformer (no prizes for guessing the product) that ran at around
370mT with 3C85 material. Fine at 25C, boom at 75C......
VBG! I would probably agree about the 78M05s, I had an abysmal fail rate on
those as well, but we weren't shattering the dies.
No experience with 78M05. I started with a simple premise: semiconductor
manufacturers products work. Surely motorola would notice 30% failure
rate.....
In general products fail because the manufacturing process abuses them in
some way. Remove the abuse, and lifetime improves. Smith & Whitehead wrote
an entire book on this subject, optimising quality in electronics assembly
IIRC.
then again, I had some 0.01% resistors from vishay that were actually
+10-25% parts! It was a dc-balance circuit in a ups, and they started
rolling off the assembly line with huge, un-correctable DC imbalances. It
took quite a bit of work to find the problem, but when I did, Vishay were
incredible! I sent them sample parts (around 100pcs were affected IIRR),
they sent me, within a week, a 30+ page report containing ESM images of the
resistive material, and a detailed analysis of what caused the problem, how
come they didnt notice (it was a material degradation, exacerbated by T, so
they started out right), how to prevent it happening again, exactly how many
and which resistors were affected, etc. And of course they replaced all the
dodgy bits for free.
I also had some fun with TI modem chips that wouldn't "shut up" when I
asserted SQT. (Squelch Transmit) The local sales weasel tried to pass it
off as ok, because there was no spec on how much the carrier level should
drop when SQT is asserted.
I was rather insistent that this should always be a very large number.
Then there was the Rockwell printer controller chip that wasn't really
tested with the mechs that they said it would work with, and the rockwell
modem chip that output a V.22bis answer tone when answering in bell 212a
mode...
or the philips micro who's RETI instruction didnt always work...but
RETI
RETI
RETI
at the end of the ISR cured the problem. 2 RETI's made it better, but didnt
fix it completely!
A company I contract to at the moment had a problem last year, with 10ns
SRAMs - our product started going mental. Turns out the SRAMs we had
purchased came from a buying house, and were 6-7 years old. The access time
was as high as 30ns in some cases, so RAM reads often returned rubbish. That
was bloody hard to find, and to prove it was the SRAM, as the designer was
beating the hell out of a CPLD, so we assumed it was a CPLD code error, and
spent weeks looking for it. And I didnt want to believe him when he said it
was the RAM, but a few simple tests proved it. We now check datecodes on all
chips, and try to only buy from the manufacturer
Too funny! Like a screen door in a submarine.
Next, non-conductive solder!
I went to a company-wide health & safety meeting once. Everyone was there,
we had to sign an attendance register. The production manager then, very
seriously, told us that lead was highly poisonous, so do not lick, chew or
eat solder - apparently some of the PCB assy staff had been seen chewing on
the stuff!
Nylon causes some other problems as well.
A fellow I'll call my "evil ex-partner", was rather insistent that we should
use Nylon and Delrin for a mechanical set, designed with very close
tolerances, because we were needing a ton of torque, and he wanted the
lowest possible friction.
This combination is kind of like twinlead, in that under ideal conditions,
it outperforms any coax cable.
However, when the prototype, which works perfectly, makes the trip from
Wisconsin in winter, to Cancun for the demo, one of the other annoying
properties of nylon shows up. It's Hygroscopic.
The tolerances went from a few mils slop, to a few mils short of an
interference fit, and the once free-spinning bearing was not turnable with
pliers.
bugger. I didnt know that about Nylon, but I'll bear it in mind, thanx.
Back in high school, I used to hang out at my dad's work where he repaired
military surveilance cameras. They gave me one to look at that they had
been puzzling over for some time. Everything seemed ok, but it just
wouldn't trip the shutter. Testing the wiring was a bear because of the
way it was built, but in a few minutes I had found the problem. It seemed
that in this camera, and in the large drawer of replacement parts, all the
solenoid plungers were made of non-magnetic metal...
even better! hey, but Aluminium is so light.....
Cheers
Terry