OK, I did a search and came up with this response from 8-13-00:

> Hi Henk,

> if I remember right, some time ago I read a question > about 7851 in the Philips forum.
> But the subject was, how can locked devices be
> reprogrammed. The answer was, never. It seems, that > the lock bits can newer be erased also in windowed
> devices.
> Maybe, they are made like fuses in old PLD devices, > which are blowed by high current.
> Please read the older Philips forum to find this
> guy.
> But I think also, you save real money and time if
> you buy new CMOS (and Flash)devices.

>Peter
>

I also checked the original comment on the Philips archive. My question is, can anyone verify this?

Reason for the question: Last week, I modified an old Needham's PB-10 programmer to handle 8751/2s. For those of you who don't know, the PB-10 was a great ISA card programmer from the 80's that handles 2716s to 2Mb flash PROMs. Very nice design, but it's not currently supported. I scoped out all of the signals, identical to programming a 2764 except for the Vpp pin, which matches pin 1 for a 32 pin EPROM. I also have the right P.3 and P.2 pin levels.

From the original Intel databook, programming the 8751H looks like a subset of the 8752BH, aside from the 21V Vpp vs. 12.5V and the don't care levels on some P.2 pins.

The Intel 8752BH I have programs fine, encryption array, lock bits, etc. (went through the UV erase/program cycle a few times). The surplus D8751Hs I have don't read, program, or patch, and I've erased them several times. Looks like the note mentioned above is correct, any further insights?

(Yes, I know there are better parts available, I'm just trying to put a tube of old parts to use in miscellaneous projects) - Claude