[Coco] FD-50X series power supplies
gene.heskett at verizon.net
Thu Oct 29 10:25:09 EDT 2009
On Thursday 29 October 2009, Chad H wrote:
>I was just wondering if anyone has ever heard of the FD-500, 501, or 502
>floppy systems' power supplies ever going bad. I have a FD-502 unit and
>it's working properly but I just came across a possible PCB part that might
>substitute as a replacement for the existing one should it ever go bad.
>But I don't want to go buying up too many extra parts if these things are
> as rock solid as they seem. Seems the older my system gets though the
> more paranoid I get about something going wrong with it. Don't need to
> turn my computer room into a parts warehouse or 'radio shack' either if I
> can help it. (maybe too late on that one)
Filter capacitors are a ticking clock, usually runs faster when not powered
up because the capacitor 'de-forms', losing capacitance slowly. Or, because
they are at heart aluminum foil, and its hard to make a gas tight joint in
foils only microns thick, they will develop high resistance connections, a
defect known as poor power factor, or excessive ESR (Equivalent Series
Resistance). But for those, keeping them on the shelf isn't great, so one
should go buy fresh ones, they don't keep for decades on the shelf. Any
capacitor whose top is bulged up from flat, or which has signs of leakage on
the bottom s/b replaced forthwith, its already bad.
Semiconductors are next, but generally speaking that's power stuff, and newer
is generally better. I rarely try for the exact same part, just use whatever
the circuit needs. I had to replace the hexfet power stage of the variable
speed spindle motor control of my Chinese milling machine a year ago. I
looked up the original one on google, then picked up a failed PC psu carcass
and checked what was in it, it was a way better part, so its in the mills VSD
now, running cooler than the original ever did. I could probably double the
size of the fuse but haven't, cheap plastic drive gears.
In those supplies, there was a resistor or two, one of which was a 1 watt, or
maybe a 2, carbon based at the time of manufacture. _Any_ of those with a
heat discoloration in the middle should be replaced by the same value in the
modern metal film 'fireproof' variety, and that is usually a 1 time job, the
new ones will still be good when the universe runs down.
Transformers are of course subject to the laws of inadequate cooling, and in
some low wattage cases, (wall warts) failure includes the solder eating away
at the joint where that 40+ gauge primary wire is soldered to the plugin lug
at some indeterminate time, sometimes in less than 3 years. For the coco's
disk drive supplies, an annual trip to the air hose to blow the dust bunnies
out should reduce those failures to the vanishing point.
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