MCUmall EPROM BIOS Chip Burner Forum
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 Using The Enhanced/Dual power Willem Programmer
 no vpp for 27cxxx

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va3nth Posted - 12/01/2005 : 20:48:23
i no longer have a vpp when programming eproms. LPT pin 16 swings to 0-1.53v when programmer plugged in, 0-5 volts without. traced to pin 12 of ic beside green and red led. looks like this is a comparator as there is programming voltage present on pin4. what is the chip so i can try replacing it?

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va3nth Posted - 12/03/2005 : 17:02:25
Thanks! 1.2k resistor in parallel with existing 'r1' did the trick..

i just assumed that I blew something as it did function before.

ZLM Posted - 12/02/2005 : 11:48:36
I assume your programmer is Enhanced version.
The Vpp is controlled by LPT port pin 1. NOT the LPT port pin 16.

It seems your LPT port pin 1 has low current output than programmer needed. So, you do not need replace the chip, only the threshold resister R1. (change to 1K see if it is works)

Please see thread following thread for more info:

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