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Making SEGA Genesis cartridges
pbj:
I've read that the only difference between an EPROM and OTP ROM is the quartz window. If you can somehow expose the internals, you can erase a OTP.
I tried my soldering iron at 900 degrees and couldn't cut through the housing.
Tried the dremel on another chip. It exposed the internals but I think went a little too far. :-\
Still working on a process... surely something will eat away the housing gently. :dunno
bulldawg:
--- Quote from: pbj on June 12, 2023, 09:08:10 am ---Are you using M27C400 or M274002? 4002 has the wrong pin out.
Okay, assuming that you're using M27C400 and your PCB is the same as pictured here:
(found on this page: https://www.pricecharting.com/game/sega-genesis/rbi-baseball-93 )
Pin 1 on the ROM is running to B7. Pin 42 is being pulled high to 5V. Your simplest fix is going to be cutting the trace on the back of the board for pin 42, and running a jumper wire from pin 42 to B8 on the edge connector. That will tell the Genesis it's a 2MB EPROM.
--- End quote ---
Well this one is going to be a no go. I was redoing my connection from pin 42 to b8 and the pad lifted up. Oh well. Thanks anyway.
pbj:
Put a jumper wire on pin 42 and try it pulled to ground and see if it boots. If it doesn't, tie it back to 5V. If that doesn't work, tie pins 1 and 42 together, and then try 5V and then ground. One of those combinations will make it work.
If you have 42 pin holes on the PCB, there's no need to lift legs, but you may have to cut traces to properly isolate the pins before you add the jumper wires.
Here's a Forgotten Worlds (512Kb ROM) on a 40 pin PCB burned to a 2MB 42 pin EPROM. I've lifted legs 1 and 42, jumped them together, and jumped to the 5V on the back of the PCB.
bulldawg:
--- Quote from: pbj on June 12, 2023, 05:29:02 pm ---Put a jumper wire on pin 42 and try it pulled to ground and see if it boots. If it doesn't, tie it back to 5V. If that doesn't work, tie pins 1 and 42 together, and then try 5V and then ground. One of those combinations will make it work.
If you have 42 pin holes on the PCB, there's no need to lift legs, but you may have to cut traces to properly isolate the pins before you add the jumper wires.
Here's a Forgotten Worlds (512Kb ROM) on a 40 pin PCB burned to a 2MB 42 pin EPROM. I've lifted legs 1 and 42, jumped them together, and jumped to the 5V on the back of the PCB.
--- End quote ---
Pin 42 to ground worked. Thanks alot.
bulldawg:
Where are you picking up 5v from? That might be what I need to fix that other pcb. The 40 pin one I have.
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