EPROM burning 21/25V 3. - Closing

The first two parts of this post:

https://pakahuszar.blogspot.com/2021/03/eprom-burning-2125v-1.html

https://pakahuszar.blogspot.com/2021/03/eprom-burning-2125v-2.html

Back in 2021 I was starting this project based on this ground:

• The TL866II is unable to handle any device programable above 18V
• My HP 8903B has 21V EPROMs and I wanted to refresh them
• The T56 programmers cost are way above the amount I would pay for this

Since then a few things happened. First I lost the ordered boards of this project. During the moving to my new lab, I was unable to find, where are those. Actually just 2-3 month ago showed up from one of my boxes. I was ordering the parts needed to build it, but had other projects to work on, so put it aside second time.

Bit later I realized that the XGECU (the manufacturer of the TL866II and T56) come out with a new programmer model the T48. It has reasonable price and the plugin modules I already bought for the TL866II are compatible with it.

Ordered it, programmed the EPROMs for my HP 8903B. So the story ends here from my perspective.

This project shelved, I not intend to build it. Maybe once, I'll try. Actually, I not even now if it id work. Anybody want to experiment with it, welcome. I can give a board for this.

Also my original TL866II will be on sale soon.

On the side of it, I planed to build a proper EPROM eraser. I ordered one, with the T48. It has mechanical timer, and not something, what I really like, but it does its job, so the EPROM eraser project also canceled.

EPROM burning 21/25V 2.

 As it wasn't a big deal project, I made the drawings fast, and ordered the boards. Also as I didn't want to use some fancy SMPS for the boost voltage conversion, so I picked the good old MC34063 used a switchable feedback divider and that's it.

The board is arriving from the JLCPCB, with the cheapest manufacturing and shipment method. I left this project laying around for a long while now. I'm not willing to pay any extra for my laziness.

EPROM burning 21/25V 1.

 After my last Fake in China post, I continued to work on the 2716 EPROM burning. I ordered a second batch of 2716's from a different source. The new series looks more promising:

Same chip size, two different date code. I think this is still a chinese copy, but may works.

Also, I've a different issue here, what I just barely realized last time.

The TL866II programmer what I use, doesn't support the 21V Vpp printed on the top of the case. Even, according to the original ST documentation, it should be 25V. The programmer only support 18V. It is not enough, even the chips would be genuine.

I found a solution in a forum: https://pinside.com/pinball/forum/topic/program-21v-25v-roms-in-lower-voltage-programmers

This is great, just I don't like it.

This is a hack solution to me. I want to have a proper adapter, I'd like to see the pin detect function still works, I want to use a regular wall wart adapter instead of a lab supply, I want to have the 21V/25V programming voltage switchable, I want to protect my TL866II from faulty chips.

I asked a question on a forum, how the pin detect function of the programmer works. On the side I had a cloudy idea in my head:

What if: I just connect the original programmer pint to the chip through a diode, while clamp the programmer side to the ground with a high value resistor. In addition use one n-channel mosfet, with a zener to detect if the voltage from the programer is more than - let say - 12V. With this n-channel mosfet pull to the ground a p-channel mosfet's gate connected to the external programming voltage and the chip's Vpp.

On the side of why even you need those chips, why you not build another programmer from scratch like answers I got to relevant:

The schematics of the TL866II:

https://proghq.org/wiki/images/3/3c/TL866II_Schematic.pdf

And a kind of solution from a german site:

https://www.dr-bosch.com/volker/umbau/index.html?#VppAdapter

This later link contains a schematic, what is exactly the same what I have in my mind except it was realized with bipolar transistors instead of mosfets

Károly Molnár, István Sümegi - Thank you for the links.

So the project starts here. The real programming in this case can wait.

In addition to the mentioned circuit I plan to add a boost converter with switchable output (21V/25V from a 12V input), plus a zener and a resistor for every pin to protect the programmer.

This is how my abandoned projects are come into existence. :-D

The design will be available here when it is ready for this:

https://gitlab.com/suf/suf-electronics-TL866II-HV-EPROM