Re: Caution on AP-64E EPROM Programmer

["Mark Cummings" <NOTfigjams@primus.com.au>]

"Patrick Schaefer" <PSchaefer@epost.de> wrote in message
3E8EE90A.13768D5B@epost.de">news:3E8EE90A.13768D5B@epost.de...
> Mark Cummings schrieb:
>
> > 1. 27128 & 27256 & 27512 EPROMs use a programming voltage of ~12.5V
instead
> > of the 21-25V Programming Voltage on most 2716, 2732 & 2764 EPROMs. This
> > would be fairly easily achievable on the TL497AC by switching in
different
> > resistance in the voltage divider on pin 1.
>
> Closing S1-7 connects a Zener diode (D2) to the Vpp line that reduces
> Vpp from 25V to 21V (for 2764 chips). You can use the same technique to
> get 12,5V.

that's a zener ??? oops looks like you just found the first error on my
diagram. I thought that was just a normal 1N914 or similar providing
negative spike protection, but a zener makes so much more sense, and it also
explains the 120 Ohm resistor feeding it. I wish they would have used ZD2
instead of D2 on the board, then I would have known.

thanks for the correction. I've already updated the diagram for those that
have the first version and want to d/l the corrected version...

http://home.iprimus.com.au/figjams/apple2/AP64Ecct.PDF


Mark