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T O P I C R E V I E W
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?
2 L A T E S T R E P L I E S (Newest First)
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.
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)