Some old EPROM needs to be programmed with a voltage VPP at 25V.

The chineese programmer TL866IIplus is a good solution for working with that old component but it only provide VPP upto 18V. But it is possible to modify it to provide a VPP of 25V.


Indeed, VPP voltage is internaly created using an MC34063 boost switching regulator. To define the voltage of the output of that regulator there is a resistors voltage divider that can be easily modified to get the right voltage for programming old EPROM. Pay attention that that mods can involve a greater current input on USB so it can fail on some computer. On mine, it works.

To do that, change R9 on the bottom PCB from 5,1kohms to 2,7kohms :

TL866 modification

To use it with the software XGPro, you have nothing to do. Let the VPP voltage on 18V :

XGPro TL866 config after mod

When you finished the use of your programmer with the mod, don’t forget to revert it to nominal condition (by putting back the 5,1Kohms resistor). If you let the 2,7Kohms on you will surely forget it and you may burn low voltage EPROM as the software does not remember you that the mod is in place.