🚀 go-pugleaf

In article <1992Dec12.223657.26231@mnemosyne.cs.du.edu> jbunch@nyx.cs.du.edu (John Bunch) writes:
>randyh@sad.hp.com (Randy Hosler) writes:
>
>>[ Article crossposted from comp.sys.atari.st.tech ]
>>[ Author was Randy Hosler ]
>>[ Posted on Tue, 8 Dec 1992 17:09:57 GMT ]
>
>>Hello all,
>
>>I recently became the owner of a 520ST upgraded to 2.5 megs and TOS 1.4.
>>Last night I opened up the box to do the Overscan mod and discovered that
>>my 520ST had the JRI simm memory upgrade.  I have no documentation on it
>>and so am hoping that someone out there can answer my questions.
>
>>I want to add another 2 megs of simms.  How do I disable the 1/2 meg that's
>>on the motherboard?  I saw one jumper on the board that plugs into the
>>video shifter.  Do I need to remove it to add the extra ram?  

You definitely need to remove the mother board RAM. It's done by clipping
two resistors on the RAM select lines at the end nearest the MMU and wiring
them to +5V.

I can't give you the numbers of the resistors, as they differ from one
revision of the circuit board to the next. You can find them by tracing the
RAM bank 0 select lines back from the MMU. This means that you need

1) A pin-out of the MMU (see the Abacus ST Internals book)
2) The ability to wield a soldering iron
3) Confidence!

>>Please post or email any and all information you may have about this upgrade.
>
>>Thanks, Randy Hosler

Mat

| Mathew Lodge                      | "I don't care how many times they go    |
| mjl-b@minster.york.ac.uk          |  up-tiddly-up-up. They're still gits."  |
| Langwith College, Uni of York, UK |  -- Blackadder Goes Forth               |