    CORRECTIONS for EPROM PROGRAMMER  (Transactor Jan 1987 by Tim Bolbach)

The following corrections are pointed out by Tim in his follow up article:
  Resistor R2 may be changed to 75 ohm if VPP LED will not light.
  The emitters of both transistors should be grounded.
  U1- Gnd pin should be 7 not 14.
  U1- Pin 13 should be connected to personality socket pin 4.
  U1- Pin 22 should have a jumper to per. socket pin 3 (original connection
      remains as shown.)
  ZIF- Pins 14 through 18 should be changed to pins 15 through 19 (pin 14
       remains gnd as shown.)
  U3- Pin 14 should be +5V. Pin 7 is gnd.

Several changes were made in the jumpers of the personality sockets:

          2716:         2732:     2764/27128:       27256:        2532:
      pin 4 to 12   pin 6 to 13   pin 2 to 20   pin 2 to 20   pin 6 to 13
          6 to 13       7 to 19       5 to 21       5 to 14       7 to 19
          7 to 19       8 to 18       6 to 15       6 to 15       8 to 18
          8 to 18       9 to 16       7 to 19       7 to 19       9 to 20
          9 to 20      10 to 23       8 to 18       8 to 18      10 to 24
         10 to 22     	 1 to 17       9 to 16       9 to 16      11 to 17
         11 to 17      12 to 24     *10 to 23      10 to 22      12 to 16
                                     11 to 17      11 to 17
                                    *12 to 24      12 to 24

* After making all of the above changes I was still able to read but not
burn a 2764. Further investigation revealed that pin 24 (VPP) going to pin 12
and then to pin 20 of the ZIF is incorrect. Pin 20 is the chip enable (CE) pin
and should never see more than +5V.	 f it does it means instant death for the
EPROM! (You may be able to read it after this happens but won't be able to
write to it and it will probably get very hot.) Therefore, change the jumpers
marked with a (*) above as follows: Pin 10 to 22 / pin 12 to 23.
With these changes made I was then able to successfully program an EPROM.
Please bear in mind that the only EPROM I've been working with is the 2764 but
these changes might apply to any of the others using these pins.

Another VERY important thing to 	 te are the programming voltages. These
appear to be very critical! Just one volt too much is enough to blow the
EPROM. The original article states that the 2764 requires +25V for VPP. I have
found (the hard way) that this should be +21V (at least for the 2764 sold by
Radio Shack.) As Tim mentioned, the best bet is to attempt to program at
several volts below that which is stated. If unsuccessful, increase by one volt
and try it again. The last one I did programmed at +19V. Always check the
Mfg's spec shee	 to be sure.
One last note is on the U/V bulb for erasing. I have been unable to find one
locally through appliance shops. They can be found in the back of Mag's such
as Radio Electronics, Hands On Electronics, etc. Although he didn't remember
which one, Tim has seen the bulb, ballast and all for as little as $9.99.
Good luck and I'd appreciate hearing about your results.
Ronald McDonald (Ron Vieira)  75766,42
