I have a 89 Jet piggy-back sitting on my shelf at home, I haven't looked at it in a while, but I don't remember seeing a window to erase the prom? Is this a flash prom? If it is will the PP erase and program it? Just wondering.

 

I have a Hyperchip sitting right in front of me, it uses a standard chip part number 27C256. Since GM is so big and they purchase so many chips, and whatever they can easily purchase chips and have them say WHATEVER they want.

Smaller Companies like Hyperchip, Jet etc USUALLY dont take the time or spend the extra money to hide such information. Even companies like SONY, Pioneer usually use standard chips and components, unless it is something that is specific to application.

Look at the chip, IF it is a EEPROM and it is a 29C256 then it should work.

I'm no expert but that has been my limited experience.

expert definition: "ex" aka as the variable "X" is referred to as an Unknown variable. "SPERT", often alternately spelled "SPURT" is a drop of water under presure. Therefore an expert or "XSPURT" is "an unknown drip under pressure"

 

I will assume that you have looked for some "lable" on the eprom and there is none. If there is any type of lable, then remove it to expose the window.

Usually, these piggy backs you can easily remove the prom from it by carefully inserting a jeweller's screwdriver between the "pins" and the socket. Be very careful when doing this so not to break the prom or bend any of the pins or openings in the socket.

Once removed, you can replace the prom with an AT29C256 Flash Prom or use a 27C256 Eprom. I prefer the Flash Prom as you can erase them electrically with the PP.

I removed the prom in my Piggy Back and replaced it with a Flash Prom and it works just fine. I then just program directly on to the PP using the "adapter" you can make yourself as outlined by Traxion's Prom Burning Introduction article.

 

I can't imagine JET or their competitors using anything other than a standard EPROM. However, they could have used an OTP (one-time programmable) device or even an EEPROM. As okfoz said, they're not a big enough fish to get house-numbered parts, but anyone could file off the numbers if they really wanted to. If there's still any markings on the chip itself, let us know and someone here should be able to decypher them.