14 Jul
2005
14 Jul
'05
8:27 p.m.
Brad Parker wrote:
Hi,
Does anyone have direct experience replacing the eproms in a M7554-PB?
The top layer says "CPU KDJ11-D". It's s-box and is labeled M7554-PB.
The eproms are 27C256's. I want to replace them with 23-261E5 and
23-262E5 images (16k, or 27C128) to turn the board into (hopefully) a
PDP-11/53.
I managed to erase two 27C128's and burn them this morning but I discovered
that the instructions I found on the web
http://users.safeaccess.com/engdahl/KDJ11.htm
don't match my board (very nice instructions, none the less - thanks!)
I may just try it and see what happens, or reprogram the 27C256's with
the image doubled, just for fun.
I just finished the board mod on an M7554-DS a month ago, and have it
running (Well, I'm out of state and it's powered down, but it ran most
of last week...) Mine is the later layout, which is what all of the
diagrams and pictures on that page represent.
Note that for both board styles, you have to add a 1K resistor to
enable the new ROMs. On yours you'll also need to clip a zero-ohm resistor.
Your board is listed as the older artwork, and there aren't pictures,
but a description of what you need to do:
"On the older artwork a similar mod is required, except you also have to
cut out a zero-ohm jumper. I don't have a picture yet, but, holding the
board with the backplane connector to the right and the front edge to
the left, and the ROMs at the bottom: the pads for the resistor are to
the left of the ROMs, and the zero ohm jumper is just above it. If you
are need to do this before I get the picture drawn, trace the circuit
from pin 27 of the ROM with an ohmeter."
If you can scan your CPU board (at a decent resolution, I'd be glad
to see if I can match a location to that description and mark where the
work needs doing. I'm also probably not he only one who'd be willing to
look at it for you.
Doc