So i recently orderd a tl866cs, to be disappointed when a tl866ii plus came to my door, as it only can produced a programming voltage of 18v vs 21v. I contacted the supplier to find out that the cs was no longer made and there is no way to get one.
After buying some 28c16s from china, none of them would program, and couldn't seem to find 28c32 with cheap enough postage, I thought i would try the m2716 that i originally ordered.
So this is how you program 21v - 25v roms in a tl866ii plus.
So, after consulting the datasheet for the pinout and programing voltage
I decided to apply 25v to Vpp pin 21 on the rom. So i bent it out of the programmer. (Make sure you bend it out, i blew up the a transistor and driver chip by leaving it in. they are not rated for the higher voltage. This was also easily fixed by replace both of them)
and applied 25v from an external power supply.
Now this will give you a pin detect error, however you can turn off pin detect.
Rom will now program as normal, and not give you any error. Hopefully there will be similar options on other programmers. This is with version 8.33 of the tl866ii plus software