west@bnrmtv.UUCP (andrew west) (02/07/89)
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I am interested in upgrading the memory in a Mac Plus. I already
have a 1M->2M upgrade from SuperMac using a "banana board" combo
of 256K SIMMs--I want to upgrade this Mac Plus to 4Meg.
Unfortunately, the SuperMac upgrade has been discontinued
(although, since they listen to the net, I'd be interested in
their response).
I opened up the Plus to see what the Mother Board looked like and
found the following:
MacPlus Mother Board
________________________
| |
| -R- R8 "256K bit" | 150 ohm resistor
| - - R9 "one row" | no resistor
| |
| _ |
| | | @E3, MMI PAL | <-- jumper,
| | | 20L8 | pins 11<->12
| - 1 |
| |
| //-------// 1 | "banana board"
| \\-------\\ 2 | "banana board"
| /////////// 3 | empty
| \\\\\\\\\\\ 4 | empty
| |
________________________
The following info is taken from Mac Tech Note #176
In the table below, R indicates that a 150 ohm resistor is in
place--a dash indicates that it has been removed. A double dash
indicates that no SIMMs are present. *Each* of the slots must
contain the SIMM indicated.
SIMMs Mac Plus Resistors
"256" "one row"
Total Mem Slot 1,2 Slot 3,4 R8 R9
512K 256K -- R R
1M 256K 256K R -
2M 1M -- - R
2.5M 1M 256K - -
4M 1M 1M - -
---------------------------------------------------------------
In the case of the SuperMac upgrade, the "banana boards" each
contain 32 32Kbit chips (= 4 * 256Kbyte SIMMs, 150ns chips used),
for a total of 1Mbyte in each of the first two slots. However,
instead of finding R8 removed and R9 inserted, I found just the
opposite--the resistors are still set up for a 1M Mac with 256K
SIMMs in each slot (R8 inserted, R9 removed).
However, there is also an extra jumper added to the CAS (Column
Address Strobe) PAL located at E3 (as shown in the Plus Mother
Board diagram). The jumper is shorting out pins 11 and 12 on the
PAL (shorting an input term to ground?).
My questions are:
1) What is SuperMac doing with CAS?
2) Can I simply remove the jumper, add two more 1M SIMMs in slots
3 and 4, and modify the resistors for a 4M configurations (i.e.
will each of the banana boards behaves as normal 1M SIMMs if the
SuperMac jumper is not present)?
3) SuperMac has added buffering to the inputs of each of the
banana boards so that the motherboard driving circuitry only sees
one load--I'm therefore not worried about overloading any drivers.
*However*, this Mac Plus is an upgrade from a 512K (with the
dreaded "black suction cup" on the video display). Even though I
added a fan long ago, is the power supply likely to give up the
ghost if two more Megs are added?
Thanks for any help,
Andrew West
{ames, amdahl, hplabs} ...!bnrmtv!west
Disclaimer: Opinions, statements and misspellings are mine!Fabian@cup.portal.com (Fabian Fabe Ramirez) (02/16/89)
Andrew, To my knowledge all that you have to do is to remove the jump and install the 1 Mb SIMMs, and then adjust the voltage (4.95-4.99) accordingly. Fabian Ramirez SuperMac Technology fabian@cup.portal.com sun!cup.portal.com!fabian
Fabian@cup.portal.com (Fabian Fabe Ramirez) (02/16/89)
Oops! I forgot to mention that you will need to cut the R-8 resistor. Fabian Ramirez SuperMac Technology fabian@cup.portal.com sun!cup.portal.com!fabian