Macintosh SE User Manual download pdf (Page 17)

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Mac. Under “About the Finder” in the Apple menu, you should see that the memory has

increased to 1MB.

For reference, the “ofﬁcial” signal names for the connections made are as follows:

TSM-12: CASL_b; TSM-13: CASH_b

TSG-3: A19

‘LS138-10R: CAS1L_b; ‘LS138-11R: CAS0L_b

‘LS138-12R: CAS1H_b; ‘LS138-13R: CAS0H_b

Pin 15 of each DRAM is CAS_b

Note that expansion to a maximum of 4MB is possible in principle if 32 1Mb chips are

used (in which case the original DRAM chips are effectively removed from the circuit),

and if the address decoding is modiﬁed accordingly. However, 1Mb DIPs have 18 pins and

a pinout that differs signiﬁcantly from that of the 256k generation, so that particular modi-

ﬁcation is only for the truly hardcore!

7.3 Keyboard Repair

Keyboard keys have to withstand considerable abuse. Physical punishment, combined

with the occasional spilled soda, can result in ﬂaky behavior, or just plain failure. Fixing

the individual keys themselves is actually straightforward; it’s getting the actual key

switch out that’s the hard part. Given that difﬁculty, it might be worth trying a quick ﬁx

ﬁrst: Some people (but not me) have had luck spraying the internal guts of the keys with

WD-40 (or similar). I always just end up with a greasy mess. Others have placed the key-

board in a dishwasher! I am not so brave, but if the keyboard otherwise seems a total loss,

I guess there’s no harm in trying one last desperate act.

If a quick ﬁx doesn’t solve the problem, you’ll have to do a little more work. First, open up

the keyboard and remove the circuit board. Gently pull off keycaps until you have cleared

a sea of keys centered around the defective key. You may wish to start from one edge of

the keyboard and work your way to the defective key. This may require the removal of lots

of keycaps, but it minimizes the risk of damaging them. Keep track of where they go.

Note the four small slots at each corner of the plastic cover of the key switch. Insert a

small jeweler’s screwdriver into one of the slots. While prying toward the nearest edge of

the switch, use a second screwdriver to pry that edge of the switch up a bit. Do the same

operation at each of the four corners of the switch. When the switch is out of the keyboard

a decent amount, gently pull it out the rest of the way by the stem that protrudes from the

middle. Warning: There’s a little spring inside, just waiting to pop out and disappear into

thin air, so be prepared for it! It’s very easy to lose.

Now that you have the switch proper out and free to work on, examine its contacts. The

typical failure mode is that the contacts fatigue a little over time, and stop working reliably

(or at all). Bending the contacts (carefully, and with tweezers or something similar) often

solves the problem (at least for a good long time). Cleaning the contacts with a product

like Cramolin or something similar may be useful in other cases. In any event, be careful

not to touch any conductive surfaces with your ﬁngers, however, or the switch contacts

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Macintosh SE User Manual Page 17