> Did You try it on another PC ?
> Maybe Your PC or its power supply produces too much noise.
> I've tried several LPT and RS232 schematics and all worked fine.

Yep, I've tried it in three pc's. Two 486/33's and a p5/100.

> The schematic is correct, but it seems that some versions of the 78L05
> power regulator draw too much current from the port.
> I've used Zener diodes in my design.

I assumed that it was drawing too much when I first encountered errors.
For testing, I removed the 78L05 and replaced it with a +5v power supply.
Is Vdd switched during programming?

> This should work.
> If not, try to connect a small capacitor (10-1000pF) between Vpp and GND.
> I can send You my TP source, if You want.

Thanks for the offer. I'll try using a zener.

> This should work under all circumstances.

Well, it works about four times a day, when I get really mad at it.

> Except if You are using a non compatible parallel port.
> That leads me back to the distortion theory.
> Try to use another PC !

Tried. Failed. :/

Jorj

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Jorj Bauer                                  |   gbauer@eniac.seas.upenn.edu
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http://binky.seas.upenn.edu/~gbauer         |         (215) 898-0575
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