I have been reading the posts about the problems with the various boards concerning not enough programming current for the NMOS EPROMS. I am posting this to get feedback as to users thoughts about the mods I did to my 4.5C dual power board from Rebios.net by way of Sivava (LONG story).
I am using a 12vdc 2a external supply with the parallel cable that came with the programmer. I have .98D5, .98D2 and .97ja software installed just for grins. The board already has hefty transistors installed for the VPP & VCC1 switching, SS8550 - 40 volt @ 1.5 amp. I beefed up the 34063 supply - changed the rectifier from a 1N4001 to a 1N5819 (silicon to shockty diode), wound a beefer 100 uH coil with 24 ga wire on a toroid and changed the 0.5 ohm resistor to 0.39 ohm. I beefed up the 7805 regulator by adding a 18 ohm 1/2 watt resistor in series with the ground leg to raise the voltage .2 volts. A 1N4001 would raise the voltage .7 volts, which would be too much for some EPROMS. The resistor modification raised the VCC1 from 4.94 volts at pin 32 to 5.1 volts. I am still toying with changing the resistor on the base of the VPP transistor from 2.2k to 1.2k. This is the resistor that is taken to ground via the NPN transistor. I also added a 4069 (using 2 gates) to feed pins 2 & 12 (Q6 & Q7) of the 4014 (4021) to pins 12 & 13. This is to speed up data reading on larger E(E)PROMS. Some boards have this circuitry and some do not, the 4.5C does not.
Current mods for Willem dual power 4.5C board
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Posted - 12/10/2008 : 03:18:58
