[Coco] Floppy controller - 7416 failure symptoms?

Mark Ormond markormond at mtxsystems.com
Mon Nov 1 22:35:57 EDT 2010

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


-----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. 


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