Solder
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What is the EPROM equivalent of a 40-pin '4M-16Bit' mask ROM?
I ask as I'm currently working on a Konami 'Bells & Whistles' PCB - the sprite colors are wrong. All other chips (custom and otherwise) are fine, so the fault must be the mask ROM at 3K or 7K.
Now somebody has already socketed the mask ROM at 3K (all connections are good) ..... and there's no mask ROM for the socket so I programmed up a replacement, namely a 27C4000 EPROM (the datasheet indicates that the internal layout and pinouts match). That passes the built-in mask ROM test just fine, but still the colors are wrong.
As an experiment I socketed the remaining mask ROM at location 7K (this passes the self-test okay too) but on putting it into my programmer and trying to read it as a 27C4000 there are errors.
So am I using the wrong EPROM at location 3K ? Perhaps the Konami self-test results are erroneous? Yet maybe not, as if I use a blank 27C4000 (or one incorrectly programmed) or no ROM/EPROM at all then the self test reports 'BAD' for the relevant EPROM.
Either way, I need to be sure that I'm using the correct EPROM type.
Any ideas please? I also can't understand why I can't read the good mask ROM as a 27C4000 - perhaps indicating that I'm using the wrong EPROM type. Yet if this is the case, why does a suitably programmed 27C4000 pass the Konami mask ROM self test okay?
Thanks
I ask as I'm currently working on a Konami 'Bells & Whistles' PCB - the sprite colors are wrong. All other chips (custom and otherwise) are fine, so the fault must be the mask ROM at 3K or 7K.
Now somebody has already socketed the mask ROM at 3K (all connections are good) ..... and there's no mask ROM for the socket so I programmed up a replacement, namely a 27C4000 EPROM (the datasheet indicates that the internal layout and pinouts match). That passes the built-in mask ROM test just fine, but still the colors are wrong.
As an experiment I socketed the remaining mask ROM at location 7K (this passes the self-test okay too) but on putting it into my programmer and trying to read it as a 27C4000 there are errors.
So am I using the wrong EPROM at location 3K ? Perhaps the Konami self-test results are erroneous? Yet maybe not, as if I use a blank 27C4000 (or one incorrectly programmed) or no ROM/EPROM at all then the self test reports 'BAD' for the relevant EPROM.
Either way, I need to be sure that I'm using the correct EPROM type.
Any ideas please? I also can't understand why I can't read the good mask ROM as a 27C4000 - perhaps indicating that I'm using the wrong EPROM type. Yet if this is the case, why does a suitably programmed 27C4000 pass the Konami mask ROM self test okay?
Thanks
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