I just upgraded my Jensen board from 16 to 32 MB. The problem is that SIMMs
with parity cost a lot more than SIMMS without parity. However, the Jensen
board uses only 1 Bit of parity per 32-bit SIMM, while there are usually 4 bits
of parity supplied on the SIMMs. So I bought 4 new PS/2 SIMMs without parity,
but with the space available to solder them on (4MB PS/2 without parity are
available for 95DM currently).
I then took 2 parity RAMs from two of my existing SIMMs (that's the point where
a hot-air SMD soldering station comes in handy), and soldered them to the new
SIMMs - this is a bit tricky, because the RAMs use SOJ packages which are
difficult to solder by hand, especially when the solder pads are just the
minimal required size - you should have quite some soldering experience, a thin
soldering iron tip and 0.5mm or 0.7mm solder for this step. After checking that
there were no shorts, and after fixing some solder joints which were not well
in the first attempt, everything works fine now.
If you really want to do this, you need to locate those RAMs which can be
removed from the old SIMMs and locate the spot where one of them is put on each
new SIMM. The Jensen uses the parity bit which is connected to pin 38 of the
SIMM module, so this should be an easy excercise compared to the rest :-)
We did this operation on two Jensen computers now (8 SIMMs total), and
everything works fine - however, if you are not sure about your soldering
abilities, you might be better advised to not try this.
BTW: we did also check a solution that would only have required soldering 4
wires to the Jensen board - this does now work because the CPU uses separate
write enable signals for each 32 bits of RAM.
cu
Michael
-- Michael Schwingen <m.schwingen@stochastik.rwth-aachen.de> Institut fuer Statistik und Wirtschaftsmathematik, | In the beginning there was Wuellnerstr. 3, 52056 Aachen | nothing, which exploded.