Alex Freed wrote:
> Steven Hirsch wrote:
>> DIP package PROMs. When my eBay purchased Advin Pilot 143 programmer 
>> arrived, I read the PROMs and, unless the programmer is defective, all 
>> of them are programmed as a chip full of 0fh values.  This is not 
>> correct and would explain the misbehavior.
> 
> My money is on the defective programmer. Can't imagine how the chips can
> get to this state if they were ever good.

No, I've checked several other types of bipolar proms and the programmer is 
just fine.  The PROMs with my DDT boards were likely programmed from the 
incorrect image or buffer.  Since they are 4-bit devices, the buffer was 
probably just a block of 0ffh (that reads as 0fh from the device since there 
are no pullups on the top 4 data bits).  The proper binary image for the PROMs 
is available and was sent with the kit.  It is about 98% 0ffh, with a few 
different 0xh values here and there.

It's also the only thing that makes sense to explain the symptoms.  NMI is not 
being vectored into the DDT firmware when the magic break button is pushed. 
One of the 74S287 chips is responsible for a portion of the logic that makes 
this happen.  I've replaced every non-programmable chip on the board, checked 
all sockets point-to-point with an ohmmeter and verified the EPROM and PAL 
programming.  All that's left are the PROMs, which appear to have the 
incorrect image.
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