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T O P I C R E V I E W
Posted - 12/10/2008 : 03:18:58 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.