[Coco] FD-50X series power supplies

[Steven Hirsch]

On Thu, 29 Oct 2009, Gene Heskett wrote:

> 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.

Can't speak for the Tandy supplies specifically, but all the external 
cases I've encountered from that era with built-in analog supplies have 
bad filter caps.  It's actually amusing how well things can sometimes 
function with essentially raw AC applied :-).

Although Gene didn't mention this specifically, it's a good idea to 
replace the usual 85-degree C caps with 105-degree units whenever 
possible.

Steve


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