dbstallman
Member
My Simpsons board has lines in some of the character sprites. In the test mode, ROM 16L has a bad checksum.
I got the logic probe and found that while all the input lines show activity, the output on pin 15 is dead, neither high nor low. The input pin that it connects to on the corresponding LS374 at location 10K (pin 3) is also dead, while the output of the LS374 is showing activity (pin 2).
Is it likely that the mask ROM has failed? I thought those were pretty robust. Would it be possible to burn a 27C800 with the correct data and piggy back it on top to test?
I have tried piggy backing a LS374 ontop of the one at 10K, but it made no difference to the ROM's checksum or in the game's graphics.
Thanks for your help.
I got the logic probe and found that while all the input lines show activity, the output on pin 15 is dead, neither high nor low. The input pin that it connects to on the corresponding LS374 at location 10K (pin 3) is also dead, while the output of the LS374 is showing activity (pin 2).
Is it likely that the mask ROM has failed? I thought those were pretty robust. Would it be possible to burn a 27C800 with the correct data and piggy back it on top to test?
I have tried piggy backing a LS374 ontop of the one at 10K, but it made no difference to the ROM's checksum or in the game's graphics.
Thanks for your help.

