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7D01/Repairs: Difference between revisions
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Old mask ROM chips frequently fail, e.g. due to electromigration problems. Unfortunately, the DF1 CPU board uses 2k×8 ROMs with pre-JEDEC pinouts (see [[Mostek MK31000]]) so there are no easy in-socket replacements. The expansion ROM in the DF2 should be compatible with a 2516 EPROM. | Old mask ROM chips frequently fail, e.g. due to electromigration problems. Unfortunately, the DF1 CPU board uses 2k×8 ROMs with pre-JEDEC pinouts (see [[Mostek MK31000]]) so there are no easy in-socket replacements. The expansion ROM in the DF2 should be compatible with a 2516 EPROM. | ||
However, there are pin headers P207, P208, P209 and P210 next to the CPU, originally used to connect the memory daughterboard or a test system, that make it easy to add a small custom piggyback board with a decoder and a more modern E(E)PROM. An 8k×8 chip (2764, 2864) is sufficient to hold the 6kB needed for the DF2. As a bonus, this upgrades a DF1 to a DF2 if the missing front panel key is added as well (pads are present on the PCB). The stock ROM chips | However, there are pin headers P207, P208, P209 and P210 next to the CPU, originally used to connect the memory daughterboard or a test system, that make it easy to add a small custom piggyback board with a decoder and a more modern E(E)PROM. An 8k×8 chip (2764, 2864) is sufficient to hold the 6kB needed for the DF2. As a bonus, this upgrades a DF1 to a DF2 if the missing front panel key is added as well (pads are present on the PCB). The stock ROM chips must be removed prior to installing the piggyback board. | ||
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