On a sunny day (Sat, 18 Sep 2021 10:25:44 +0100) it happened Martin Brown
> wrote in <si4bao$1rp4$2...@gioia.aioe.org
>How to do it optimally has been known for around a couple of decades.
>The old traditional way was to try and avoid all critical in service
>failures by replacing still working parts before they reached MTBF.
>We christened it causative maintenance since it was pot luck whether or
>not the damn mainframe would come back up again after a manufacturers
In my TV days we would run shifts and if something failed fix it ASAP
there was also some redundancy in equipment so you could divert operations.
One day there was some genius who decided to reduce interruptions in
the broadcasts to make a 'preventive maintenance' group, and to work those engineers went,,,
Basically with Ampex quadruplex video recorders that meant taking one apart and putting it back together again.
The usual things we already did on schedule, like replacing recording heads etc.
Disassembling and putting back together solid state electronics does not really help,
'if it ain't broken do not fix it;
Anyways one machine started to produce little black spots every now and then in the picture,
It was sidelined, and several engineers had a go.
One evening I had the late night shift, not much to do,
everything worked, so I decided to have a look at that machine,
Took the scope cart, Tek, could detect strong impulses everywhere, was midnight and we went off air (in those days),
so I wrote in the book for the next shift 'seen pulses everywhere, looks like a shield is lose'.
My boss, it was his turn next morning, he read that remark and spend the whole day taking the thing apart, no luck.
Next day it was my shift, took all circuit diagrams, scope and went for it.
The pulses reminded me of some tacho signal used,
found the pulse generator and followed its output via a coax cable that send it to an other unit,
PL259 connector, was sort of lose, screwed it back on tight, problem fixed.
10 minutes.... Went back with all the books and scope card and said: Hey guys, let's go get some coffee.
All the faces there in disbelief.. OK, I said I will show you and reproduce it,..
So how did that cable come lose? The preventive maintenance group had forgotten to tighten that PL259 connector.