[Coco] Disk Drive FD 501 Floppy

[Gene Heskett]

On Sunday 14 April 2019 23:17:59 Melanie and John Mark Mobley wrote:

> If I let my floppy drive warm up (stay turned on for 25 minutes) then
> I can boot OS9.
> If I do not let it warm up then it hangs after two lines of "..."
> dots. What could be wrong with my 501 floppy drive or 501 floppy
> controller? If I turn off the computer but leave on the floppy drive
> for a cool down time, then turn the computer back on it will work just
> fine.  So the problem is with the floppy drive or floppy controller.
> Another time we swapped out the floppy drive and that fixed it, so
> that narrows it down to the floppy drive.
> How many parts make up the floppy drive?  Power supply, Floppy drive 0
> & 2., Floppy drive 1 & 3, and ribbon cable.
> The ribbon cable is new.
> Should I swap floppy drive 0 & 2 for floppy drive 1 & 3?
> What adjustments can be made to floppy drives?  Fix the power supply,
> belt, rpm, head alignment, ...
> Can I get it repaired at the CoCoFEST?
>
> John Mark Mobley

I am a C.E.T. At their advanced age John, and the symptoms you describe, 
my bet is on the physically big filter caps in the supply being "dried 
out". This causes a loss of capacitance, and a rise in the ESR. ESR is 
equivalent series resistance, generally caused by oxidized connections 
between the foil of the capacitor, and the terminal you see coming out 
of the bottom where the wires are soldered on.

Disassemble it to where you can see them, and if the tops of the cans are 
bulged, (generally indicating high ESR which causes heating, which may 
get better at higher temps) or the base shows any whitish leakage, 
replace them with more modern equivalents for voltage and capacity.  You 
can generally go up in capacity, but not down in voltage unless they are 
35 or 50 volt parts now, in which case you can go down to 16 volts as 
the supply for the motors is 12, and there's generally a regulator to 
make 5 for the drives logic. It may have a smaller cap on its output, in 
which case replace it too.  The capacitance is not super critical, but 
the ESR is.

But few test meters can do a decent job of measuring ESR. The best one 
(the Capacitor Wizard) is $200 or more. If any doubt, replace.

Generally, an electrolytic capacitor will stay "formed" longer if they 
are being operated right at their nameplate voltage, but caps marked 6.3 
and 16 volts so they are in the top 30% of their voltage rating will 
work and almost as long. A 50 volt cap, in a 5 volt circuit, has got to 
be about dead by now.

If you aren't handy with a soldering iron and rosin cored solder and own 
a solder sucker, there are several on this list who are.  And are 
probably within a Saturday trips driving range, I am not.

Take care you two.

Cheers, Gene Heskett
-- 
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