[TenTec] Corsair II UV EPROM failure

[geoffrey mendelson]

On 2/15/2014 3:12 AM, A R wrote:
> Oh, man! Clayton, you're my hero. The prom is a 28-pin, and is UV programmable, rather that EE programmable. I believe the programming of my prom is good. It's just an input gate that's stuck low. If that's not a problem for downloading (if input gate states are not needed), then my prom should be good for acquiring the program.

The UV applies to the E not the PROM part of the name. To be exact, the 
chip is a microprocessor with a UV erasable PROM attached. To erase the 
contents of the PROM in the package, you expose it to high intensity UV 
light.

Programming the chip is unfortunately far more complex.

First you program a 2764 EPROM (also UV erased, but not relevant to 
programming the microprocessor) with the desired data. 2764 chips are 
relatively easy to find, you can get all you want used, erased, and 
tested for under $2 each on eBay including postage. They are programmed 
with the under $50 programmers you see on eBay. Although if I had to do 
it again, I would spend $150 on a USB connected Wilem programmer with 
the complete kit of device adapters, but I digress.

The hard part is transferring data from the 2764 chip to the 
microprocessor. That is accomplished with a special programming device 
that boots up the microprocessor, and sets the program bit on. The 
microprocessor boot code senses this bit, and reads data from the 
attached 2764 and copies it to the chip.

If you try to program the microprocessor without a 2764, it will program 
it with worthless (I think all FF) data, you have to erase it (with the 
UV light) and start over.

The second link to a programmer is actually to a device that copies the 
EPROM part of the chip to SDRAM and rewrites it to a fresh chip, There 
are ways mentioned, but not detailed, to copy that data to a PC, so you 
can program more than one, or archive it for later use.

  Here are some useful links:

http://www.penguinet.net/TailChao/Extras/MC68705P3/MC68705P3%20Programming%20Module.pdf
http://www.alldatasheet.com/datasheet-pdf/pdf/77313/MOTOROLA/MC68705P3S.html

http://matthieu.benoit.free.fr/MC68705P3_reader.htm

And while you are at it, a UV eraser sells for under $20 on eBay.

Basically if you are handy with a soldering iron, have some computer 
savvy, and want to do something new, you can get the whole setup for 
around $100. Obviously it would be cheaper and easier to find someone 
who knows what they are doing already, and has all the equipment.

Geoff.

-- 
Geoffrey S. Mendelson 4X1GM/N3OWJ
Jerusalem Israel.