[Coco] FD-50X series power supplies

Gene Heskett gene.heskett at verizon.net
Thu Oct 29 13:39:31 EDT 2009

On Thursday 29 October 2009, Steven Hirsch wrote:
>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 :-).

Chuckle, yes, I've made that observation 2 or 3 times. :-)

>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
I'll second that, but 105C caps are often going to be made out of pure 
unobtainium for the more remotely located users.  The 85C cap is fine if a 
fan that can actually pull or push external air through the case is 
installed, and those can be had from old cpu coolers or pc psu's for free.

Letting the case get that warm that you need the 105C caps, is going to 
shorten the drive and media life considerably.  The fan is much the _cooler_ 

Cheers, Gene
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