I got a tll 866ii plus eprom burner and apparently if you crank up vpp to 21v with a bench power supply it can do the trick. it is just opening another can of worms that id rather avoid - if positive reinforcement is staying absent i will likely just sell the pets without board - should work ideal for mini 40 or such as keyboard monitor and case are almost mint. i actually own a pro log m900 eprom burner from the 70s based on a 4004 (for sale to fund my other retro invests) but i got no way to get the data on that heavyweight. i am missing the actual eprom ics and a uv light. and i am not very interested to learn how to compile assembler as of right now.
You might be right about cranking the voltage up to 21V, sometimes these Uveproms can give trouble unless they are the correct versions for the correct programming voltage , generally the eproms with the "A" suffix are the 21V versions. You don't have to bother buying a UV eraser if you buy NOS eproms that have never been programmed.
Your idea to sell the PETs without their broken original boards is a really bad one.
A person would much rather buy the PET in the original condition with its original board (many enthusiasts can fix these boards themselves). Also, there is the repair support here with the major contribution from excellent teachers like
@daver2, but for this to work, the student has to be motivated and patient and willing to learn.
For example I know one person with an original PET housing with the PET mini board in it and they are disappointed with its performance (some issue with the screen pixels not visible on the L) so they are trying to build another, but they want an original PET board !
My advice is, leave the original boards in your PETs , not only will it increase their sale value, but it preserves their history.
In the future it pays to keep one thing in mind. (this same applies to all vintage electronics). Most people interested in buying this stuff don't expect that it will be working 100% or at all. And they expect they will have to do some restoration and fault finding, it is part of the fun of vintage computing.
I think most buyers would much rather buy something original and untouched from a seller.
If the seller is inexperienced in repairs, lacks the correct diagnostic equipment and workshop equipment and skills, and tampers with the circuitry, that really puts people off, because they know this sort of thing introduces more faults and damage, especially pcb damage where parts are unnecessarily removed and replaced with poor de-soldering skills. Or say running a CRT for too long with a bright spot and no beam deflection, it damages the phosphor. No repair is a lot better than a botched repair.
One other example of this is in the field of vintage transistor radio collecting. Many sellers do things like re-cap the transistor radios in an attempt to get them working, and a lot of the time they "get lucky" and the radio works, as they are quite simple devices. However if I see one the seller has re-capped, I never buy it, or even consider it, because these radios have very delicate phenolic pcb's. It requires special de-soldering techniques and exact soldering temperatures not to lift the pcb's foils and damage the vintage germanium transistors too. Every seller re-capped version I have seen has damage, so I avoid them like the plague and only buy un-touched radios, working or not. The sellers probably don't know they are putting some buyers off.