In article om,
"Henry Kolesnik" wrote:

I was a GCA radar tech in the RCAF in the 1960s and in one of the excercises
(war games) we had to find and fix a fault so the incoming aircraft
wouldn't crash, it was zero visibility . Sometimes it was as easy as a bad
or loose tube, but some seargents had subchassis with cold solder joints,
shorted black beauty capacitors or fried resistors. Time was critcal as the
weather was closing fast and the aircraft was low on fuel. Sometimes the
excercise left us without many parts, partially functional test equpt, and
only partial manuals. To better simulate battle conditions, one end of the
hut could be on fire and CO2 smoke to hinder visibilty! A shorted .01 uF
400VDC black beauty was easliy replaced with a .01 uF 600VDC or .02 a fried
22K 1/2 watt with a 22K 2 watt or something close. Color codes were quite
useful in many cases. The objective was to save the aircraft using limited
resources. Today I don't think we see component level repair in the field
but in battle anything may be necessary for survival. I'd much rather have
something with component values rather than a bunch of codes that required
decifering. I still contend this is a result of "military intelligence."
And the codes make it tough on us hobbyists but we not under a critical time
crunch and with the Internet it's usually a piece of cake.

In the sixties that was possible. But now you can't really fly by the
seat of your pants. Repair is by replacing LRUs (Least Replaceable
Units). Even if the LRU makes it back to the depot for failure
confirmation, it may not be repairable. 6, 8 or 12 layer PCBs cannot be
readily repaired. And would you trust one that was repaired if it did
not go through a burn-in cycle afterward? Would you depend on a
fail-safe circuit to prevent a nuclear launch if it had a component
replaced in it that was "close enough?" Maybe in your cars brake system,
but not on my missile!

Al

--
There's never enough time to do it right the first time.......