[Coco] Floppy controller - 7416 failure symptoms?

[jdaggett at gate.net]

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