18 Jul
2005
18 Jul
'05
6:39 p.m.
Doc Shipley wrote:
...
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.
That is a very kind offer, thanks.
For the record this is a M7554-PB cpu board.
I beeped out the zero ohm resistor which connects to pin 27 on the
EPROMS. Pin 27 is A14 on a 27C256 and PGM# on a 27C128. The zero ohm
(a resistor with a single black band) is just in front of what looks
like a mask prom "LM8722 116C6". This is an unsocketed chip the same
size as the EPROMs and next to them.
I also found the site for the pullup, which pulls PGM# high when using
27C128's. It's site straddles the two EPROMS and is just above them.
If you beep out the pads you find one connects to pin 27 on both EPROMs
and one side connects to pin 28 on both (Vcc), which makes sense.
My current digital camera is not very high res, sorry. Here are three
800k uncropped jpeg's.
http://www.heeltoe.com/retro/KDJ11/IM001369.JPG
http://www.heeltoe.com/retro/KDJ11/IM001370.JPG
http://www.heeltoe.com/retro/KDJ11/IM001372.JPG
If these are too poor just say so and I'll borrow a better camera.
Having said all this I'm sort to tempted to leave the board unmodified
and just erase and reprogram the 27C256's. Is there any downside to
doubling up the 23-261E5/262E5 binary images and programming them into
the 27C256's?
-brad
