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Re: [N8VEM-S100:5417] ZFDC Write Protect Issues

Well John gets the award.... 

When I was ordering parts for this board I had bought some parts from eBay that came from China.  Early on in the build, the board would not pass some of the initial build steps and it turned out one of the 74LS02's (U37) simply did not work.  When I replaced it with another from Digikey the system passed.

Now, John's comment got me thinking about the connector and as it turns out I had purchased the 9 pin 150 ohm RR4 just below it from China as well.   Guess what?  There is no continuity between any pin, much less pin 1 and the other 8!

That was obviously affecting these signals

I happened to have a good quality 200 ohm package and as soon as I replaced it my problems went away - write protect is now normal.

The board will now format, read and write tracks perfectly on the 3.5" from the diagnostic..   It is not recognized as drive 'C' in my non banked no holes IDE system, but that will be the next step.

Thanks for all the great advice,


On Tuesday, October 21, 2014 10:26:24 PM UTC-4, Gary Kaufman wrote:
Thomas -

I was having similar symptoms also, which ultimately turned out to be my
<stupid> miss-adjustment of the data separator.

As I was debugging the ZFDC I also had a bad 2793, and 2 counterfeit Z80's.

I've had good luck with  2793's from acpsurplus (California) or
arhavelectronics (Israel) on Ebay
Avoid any Z80 from China.

It took me a while to get the board working properly, but it's rock
solid now.

- Gary

On 10/21/2014 10:00 PM, John Monahan wrote:
> Did you get the data separator setting setup correctly.
> John