[Coco] Floppy controller - 7416 failure symptoms?

Gene Heskett gene.heskett at gmail.com
Mon Nov 1 22:57:05 EDT 2010

On Monday, November 01, 2010 10:40:07 pm Mark Ormond did opine:

> I'm having faulty read/writes I still don't have a second floppy drive
> to test with so I'm also checking to see if it could be the controller.
> The drive will also only format a few older disks and none of my newer
> ones (dsdd). These disk work fine in a commodore 1541 drive. (and yes
> they have the single sector hole). The disks it does format are not
> reliable.
> I have a lead on a couple of drives from a Compaq portable one I guess
> when they come in we will see what is actually the problem
> Later,
> dabone

A couple things come to mind here.  The plastic 'rosette' that clamps the 
disk to the drive spindle may not be doing its job as the plastic tends to 
relax if left in a closed position for a couple decades. :)  This also 
allows the disk to not be well centered, and can make itself known at times 
by the slightly damaged edges of the spindle hole, because the rosette also 
shrinks as it relaxes.  The phenomenon is called cold flow.

And, if the spindle is belt driven, same deal, the belts stretch and start 
slipping after a couple decades.

One of the hazards of trying to care for 25 year old stuff.  There are some 
belt treatments about but I've not had any great luck with them myself.

Just recently, I was re-installing the latest ubuntu on my milling machines 
computer and the cdrom drive would not open.  That teeny little square 
rubber belt that drives the tray had stretched and was slipping.  So I 
located my newest container of superglue, sharpened my knife and cut 1/8" 
out of the belt & glued it back together.  Worked like brand new long 
enough to do the fresh install.  I have no idea if one could do that, given 
steady enough hands, with the flat belts in an old drive or not.  OTOH, if 
it doesn't work, you aren't out more than the price of the tube of 
superglue and your time.  Do keep a quart of acetone handy in case you glue 
your fingers too.  Don't ask me how I know... ;(  It can also serve to clean 
the belt and make the superglue hold a lot better.

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
> On Behalf Of jdaggett at gate.net Sent: Monday, November 01, 2010 7:22 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] Floppy controller - 7416 failure symptoms?
> On 31 Oct 2010 at 23:58, Mark Ormond wrote:
> > Still trouble shooting floppy problems and was wondering if anyone can
> > tell me type symptoms that failing 7416 chips would have in a
> > controller? It's a fd500.
> The 7416 is Open Collector Hex inverter. It has the capability of
> sinking 40 mA of current when the output voltage is low.
> Failure would be recognized by no switching of the output of a gate(s)
> when the input changes level.  Failure can be the output transistor of
> the gate failed internally to the device or a failure of the pullup
> resistor. Also check the pullup resistors for open or poor 0solder
> joint. Since the device is an Open Collector to source current it must
> have an external pullup resistor. That value along with voltage will
> determine source current.
> james
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Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
	"Say, you look pretty athletic.  What say we put a pair of tennis
	shoes on you and run you into the wall?"

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