Ethan Dicks wrote:
Typical of a machine that has good video but something
is wrong
between the CPU, RAM and ROM.
Just going through the motions of reseating chips (again - tried once, but
doesn't hurt to do it a second time!)
Does anyone have a photo, PCB layout, or access to a real board so that they
can check ROM chip locations for me?
The 6540 ROMs in mine are arranged (left to right) as:
018 (PCB loc. H7)
014 (PCB loc. H6)
012 (PCB loc. H5)
016 (PCB loc. H4)
015 (PCB loc. H3)
013 (PCB loc. H2)
019 (PCB loc. H1)
(6540 #010 is at the back-right of the board, location A2/A3. Character table,
I assume)
Seems a bit odd - I'm just surprised that they aren't linear. Odd that there's
no 017 either, but then there's no 011 - possibly they did that so the two
couldn't be mixed up.
Date codes are all in 1978, so presumably I'm looking at a first issue of the
ROMs?
I'd just like to rule out that someone hasn't pulled the ROMs on this at some
point and put them back in the wrong positions :-) (annoyingly the schematic
correlates ROM memory location with PCB location, but not ROM part number with
PCB location)
There were two kinds of static PETs - early ones with
256x4 memory
(5101s?) and later ones with 2114s. The 2114s were only in use for a
short time, and are somewhat rare.
6550's in this one...
The recommended procedure when suspecting bad SRAM
chips is to swap
the top set for the bottom set.
Will give that a go if re-seating everything again doesn't work. And 'scope
the /CS line...
cheers
Jules
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