All About The Apple IIc
By Hank Levinson
Copyright (c) 1996 by Hank Levinson

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The Apple IIc comes in several varieties. The first models did not support 3.5"
UniDisk drives; the latter "memory enhancement" models did. I will explain here
how to enhance an early model to allow a 3.5" UniDisk to be used with an Apple

First there is the problem of how to recognise an early model from a "memory
enhancement" model. Most memory enhancement models have a "Model No." somewhere
on their undersides of A2S4100. The earlier models were A2S4000. But this is not
always reliable. It is best to open an Apple IIc and LOOK. I will not describe
how to open an Apple IIc case; you may find directions in any memory enhancement
kit for the computer ( A.E. or the Apple board itself). Lift the keyboard up,
being gentle with its ribbon cable connector, and look under it. In the row of
components at the front of the computer are two large chips. The larger of the
two (40 pins) is the 65C02 CPU which is the heart of the IIc. If there is a
female connector to the right of the 65C02, then you have an expansion model.
(The connector takes Apple's 1 Meg memory expansion board.) If not, you have an
earlier model.

Let us assume you do have the earlier model. Next to the 65C02 chip, at its left,
is the computer's ROM chip. It is labeled MON (on the lower left on the green
board), and at its upper left is a "jumper" labeled W1. This looks like two
arrows, tip to tip. If there is a cut between these tips then your IIc has
already been modified to accept 3.5" UniDisk drives. Close your IIc and try
booting from a UniDisk 3.5" drive connected to the disk drive port at the rear of
your machine. (Use ONLY the 3.5" UniDrive. Ordinary 3.5" drives can DAMAGE a

If the two tips of the arrows in the W1 jumper touch, we must modify the
situation. Again there are two models to consider. To the left of the (28- pin)
ROM chip there may either be six holes (4 large, 2 small with diameters
approximately like a ball-point pen) or there may be no holes, and a row of
resistors and two small (8-pin) chips. If the resistors and chips are present,
you do not have to do too much. If there is simply space for them, then you must
obtain them and solder them where indicated.

The resistors, from left to right, are labeled as follows. I also give their
values so you may buy them in any electronics supply house (such as Radio Shack,
etc.) R11 = 11K.ohm 2%tol. R21 = 10K.2%, R22 = 100K.2%, then there is an LM311
chip with its notch at the left. Next, still reading from left to right, is R13 =
10K.2%, R14 = 5.1K., R12 = 10K. and R15 = 1K. The last three resistors may be 5%
tolerance, the first four should be 1% but you may use 2% instead of the very
hard to get 1% resistors.

In addition to these resistors, you will need the LM311 chip, and an NE555 chip
together with a capacitor, labeled C51 = 4.7 microfarads, 35Volts. Be careful to
insert this capacitor with its "+" and "-" wires in their proper (labeled) places
in the board.

In order to insert and solder all these things onto the main logic board, one
must remove the board entirely from the IIc case, and desolder the little
receptacles. I use a solder-sucker bulb; it is the most gentle way.

The ROM chip used in the IIc models which did not support 3.5" UniDisk drives
were 128K; either 23128 or 27128 chips. to upgrade for 3.5" UniDisk
compatibility, a 256K ROM is needed. They are obtainable from Alltech, or they
may be copied to a blank 27256 EPROM using an "EPROM burner". Since the data on
the ROM chip is copyrighted by Apple, copying this ROM is probably illegal.
However, I believe Apple no longer makes IIc's, so I don't really know the
propriety of this.

Once all the components are installed, all that remains is to make a small
incision between the tips of the arrows in jumper W1, and to connect the two
semicircular pads of jumper W2 with a bead of solder. (W2 is just above the MMU
chip which is just next to and parallel with the 65C02 CPU chip.) Now your IIc
will support a 3.5" UniDisk drive, and you may enjoy greater disk capacity.
Returning to those early boards which had six holes in place of the circuitry we
just discussed and restored, such boards do not have jumper W2. To upgrade such a
board, simply replace its 128K ROM (be sure it isn't already a 256K ROM) with a
256K ROM, and cut jumpers W1, W5 and W6, near the AUX SPKR jack at the front left
corner of the board. Close the patient and resucitate with electricity from an
Apple IIc power supply (the brick on a leash.)

To enhance the memory of an early model Apple IIc without a memory expansion
socket, use a board made by A.E. (Z-RAM) or its equivalents. These boards fit
into the 65C02 socket, and the 65C02 chip fits into another socket on such an
expansion boards. The only problem with these boards is that they are very tricky
to seat properly in the 65C02 socket, and they also need their own software
patches so that AppleWorks, or WhatEver, will recognise the extra memory they
contain. But aside from this, they work just fine, and even allow one to use
AppleWorks 5.0 on a IIc. (AppleWorks 5.0 requires at least 256K of RAM.)