Cleveland, OH
Just curious. Later editions of the system 6 board took out u9 and u10. If you've got a non-booting board that's using IC14 only, can a bad u9/u10 be the cause? Or are they simply not used?
(Topic ID: 211865)
Quoted from CadillacMusic:Just curious. Later editions of the system 6 board took out u9 and u10. If you've got a non-booting board that's using IC14 only, can a bad u9/u10 be the cause? Or are they simply not used?
They can be the cause. They strength the data lines, so all that data is going through them. If either fails slightly, it'll kill your entire data bus and the CPU won't be able to access anything. I've removed them a few times and replaced them with jumpers and gotten boards booting.
Quoted from CadillacMusic:Cool. Just jump them like they're jumped on the later boards, I assume?
Yes. If you are not worried about saving the chip cut him out and use the remaining leads to bridge over the data in to data out.
Looking with scope on the data in and out will show a problem. Those data buffers for sure can cause a lock up.
I believe the theory was when they where using six masked ROMs they needed the data buffers. If you go to three eprom setup, specially with 27c16 ROMs, there is no worries.
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