Comments for page: 1702A EPROM Programmer

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Posted by Va3qe February 03, 2019 - 11:15 am
I finally got around to building one, but I am having trouble getting it to read or burn EPROMS. I have checked the wiring and I am reasonably sure it's correct. The second LPT port seems to be working. Its setup as BPP.

For reading, it always says the results are all 00's. The read LED come on as soon as I apply power.

When I try and burn an EPROM, it appears to be doing it, as inner the relay clicking, but I don't see the write LED lit, and when I read the EPROM using another reader, it shows blank.

Running DOS 6.22 on an older Pentium machine.

Any ideas what to check next?

Posted by Steve L. June 24, 2018 - 08:37 pm
That sounds like an excellent project. I'd be very interested in covering it as an addendum to the article if you're up for that (with full credit of course). The serial interface would be SO much easier for folks to use these days. Feel free to contact me if I can help in any way. My email address is on the about page, accessible with the button on the Home page.

Posted by Andi8086 June 24, 2018 - 06:02 pm
Thanks :) That makes sense then. I am currently resdesigning it with an Atmega Microcontroller to which I want to talk via serial. I will be happy to share it if it works.

Posted by Steve L. June 24, 2018 - 03:46 pm
Hi Andi8086 and thank you for the interesting question! The answer lies in the fact that the Vgg pin of the 1702A is expected to source current during the programming. The programmer hardware only needs to pull it down or let it go to the +47V rail. Since the specs require that it only be pulled down to about +10V, the Zener is placed in series with the pull-down driver, Q1. I will be happy to help if you have any other questions.

Posted by Andi8086 June 24, 2018 - 01:23 pm
Hi, I don't understand the Zener Diode in your circuit. The forward voltage usually is around 0.3 Volts or so, which means, that you get 46.7 Volts on VGG. Okay so far, but how do you get 10 Volts... there is nothing connected to the pin anymore if the Diode blocks, i.e. Ground on one side and the pin on the other side. Is it with remaining charge on Vgg itself?

Posted by VA3QE May 03, 2017 - 08:12 am
Thanks. That saves me a lot of time drawing it out from scratch.

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