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Re: [N8VEM-S100:5420] ZFDC Write Protect Issues

I agree with this order or some variation of it (personally I like to go to Digikey before Jameco because I can build nice parts lists there and re-use them, but it did take several projects to learn the ins and outs of Digikey).

I would add to the list Quest Components which is also in CA.  I ordered several UPD7220, BT478, and WD37C65 chips from them and they were excellently packaged with desiccant and everything.  They also have a lot of the support chips for the 286 and 386 boards, including some faster variants that John mentioned looking for in his writeups.....

On Wednesday, October 22, 2014 10:09:25 AM UTC-7, monahanz wrote:

Guys do yourselves a favor get stuff like this from Jameco.  The price difference on things like this are trivial particularly when you count shipping.  Life is too short, the time you spend on these things is just not worth the savings.  FWIW,  I always use in this order:-

Jameco, Mouser, Anchor Electronics, & Unicorn Electronics. If not available in US, then UTSource.  





From: n8ve...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Thomas Owen
Sent: Wednesday, October 22, 2014 9:05 AM
To: n8ve...@googlegroups.com
Subject: Re: [N8VEM-S100:5420] 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








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

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