Meat Plow said:
LOL pretty reliable and you repair that many?
Hey Meat, how's it going?
Perhaps you misunderstood what I said. I stated that I repaired 6 or 7
hundred a year of a particular board that happens to *use* an LM317T. I then
went on to explain that of those several hundred, *very few* of the faults
that the boards had, were related to that '317.
Actually, I've just looked at the figures, and I do about 100 every 6 weeks,
so it's actually nearer 800 a year. This board has an LM317T and a 7805 on
it, neither of which are heatsunk by anything other than being screwed down
( and often not very well ) to the PCB. Both of these regs run too hot to
touch in normal use. I have a separate spares drawer cabinet for the repair
of these, and in it, I keep a running stock of 5 LM317's, which I replenish
perhaps once a year. The very occasional power supply faults that these
boards suffer on their 12v rail, which the '317 is used to derive from the
raw 24v supply, are almost invariably o/c surface mount R's in the voltage
set network, or s/c tantalum surface mount caps.
Considering that these devices are s/c, thermal, and SOA protected, this
pretty much puts them outside being damaged by external conditions, so any
failures have to be random chance. Semicon manufacturers have got random
chance failures, after the bottom of the bathtub, licked these days, so I
don't see why you find the fact that I don't have very much trouble with the
317's, given the number that pass by me, funny ??
Do you have some other experience of them ? Am I alone in not seeing a big
reliability problem ? Just interested ... d;~}
Arfa
