AOH :: REU1764.TXT|
Upgrading a Commodore 1764 REU to 512k
HOW TO EXPAND YOUR 1764 FROM 256K TO 512K
The 1764 RAM Expansion Unit (REU) consists of a plug in cartridge and
a beefier power supply. This power supply is required because the
original C-64 power supply was not designed to meet the current
requirements of the additional IC's in the REU. The new power supply
is rated at 2.5A at 5 VDC and 1A at 9 VAC. The DC supply was
increased for the additional RAM.
The 1764 REU is merely a printed circuit board (PCB) inside a metal
housing which is inside the plastic case. This assembly plugs into
the Expansion Port of the C-64 or 64-C computers. The PCB is the same
board that is used in the 1700 (128K) and the 1750 (512K) Expansions
with a couple of differences:
1) The 1764 has only one bank of eight 256K Dynamic Random Access
Memory (DRAM) IC's. Each IC holds 256K bits of information;
therefore, 8 IC's are needed to obtain 256K bytes.
2) There is a empty bank of 8 positions labelled Bank II on the PCB.
3) There is a resistor (most likely R4) in the 1700 and the 1750
REU's that was omitted in the 1764, apparently due to a small
difference in the Expansion Port of the C-128 and the C-64. In spite
of this difference there are many C-64 users that have installed the
1750 REU without problems. Please note; you cannot use the original
power supply in this manner. You MUST use a power supply that has
more current on the DC side.
Commodore likely decided to ship the 1764 with only 256K to keep the
price of the unit down and make it attractive to as many C-64 owners
as possible. Only by selling a significant quantity of the 1764 would
it be possible to entice software companies to support it. The
RAMDISK software included with the 1764 is a nice option, but it is
not compatible with many software packages since it only supports the
4 file types (PRG, SEQ, USR and REL). The RAMDISK does not support
direct track-sector access, which many programs use for loading and
It is not too difficult for someone with a reasonable knowledge of
soldering to install the additional IC's in Bank II on the PCB. You
may want to install IC sockets on the board to avoid damaging the
DRAMs. Bank I is not in sockets. It is possible to solder the IC's
directly into the board without heat damage. If you feel hesitant
about doing so, you will probably want to use the sockets.
The DRAMs you need to acquire are 256K, 150 ns access time. The
industry part number is 41256-15. They can be obtained at many
electronics parts houses, mail order and Radio Shack. The Radio Shack
P/N is 276-1252. Their price is $6.95 each. With the recent embargo
on memory IC's look for these to become harder and harder to find.
You will need a quantity of eight. The following steps should only be
undertaken by someone skilled in handling PCB's and soldering. Some
mechanical skill is needed to remove and install the PC board in its
NOTE: Be careful to avoid ESD (Electrostatic Discharge) damage to your PCB
assembly. If possible, use a wrist strap attached to a grounded metal pipe
or such. Only a few hundred volts of Electrostatic potential can
completely ruin your REU.
STEP 1 - The housing of the 1764 must be opened. There are 4 pins, one in
each corner. Starting at the opening which connects the unit to the
computer gently, but firmly, pull the top and bottom apart. The plastic
case will begin to separate. Continue around the perimeter of the case
until the top can be removed from the bottom.
STEP 2 - Remove the metal shield from the plastic case by pulling it out at
each corner. The PCB is inside this metal shell. Open the shield starting
at the connector opening. You may need a small screwdriver to bend the
metal slightly where the two lips meet. When the shield opens, spread it
only as far as needed to remove the PCB.
STEP 3 - Examine the PC board. Bank I is the row of eight IC's along the
top edge of the board. The RAM Expansion Controller (REC) is the square
component in the middle of the board. The Bank II row is just below Bank
STEP 4 - Your PCB was most likely wave soldered. Therefore, the holes that
you must insert the new IC's in are already filled with solder. The best
way to remove this solder and open the holes is with a vacuum desoldering
tool. One can be purchased at Radio Shack (P/N 64-2120) for only $6.95.
Make this investment. You be glad you did! Remove the solder from all
holes; 128 in all. Be careful of how much heat you apply during this
process. Do not break or pull up any of the traces attached to the holes
that you are desoldering.
STEP 5 - If you are using IC sockets, solder them into the board with the
pin 1 end towards Bank I. Then insert the new IC's into the sockets being
careful to engage all pins in the proper sockets. If you are not using the
sockets, solder the actual IC's into the board with the pin 1 end toward
STEP 6 - Reassemble the unit in the reverse order of disassembly. Be sure
everything fits properly as it was before you began.
STEP 7 - The REU will now hold twice as much as before. If you are a GEOS
user, you will see that 512K is installed when you use the CONFIGURE file.
You can now shadow two drives, or have one drive shadowed and one RAMDISK.
If the REU is not operating properly please check the following:
A pin (or pins) is not soldered correctly.
A trace (or traces) is broken (open) and not making contact.
A solder bridge exists between two adjacent traces or holes.
One (or more) IC is defective. Almost all DRAMs receive 100% testing
during manufacturing. This is an unlikely reason for improper
operation. However it is still a possibility.
Obviuosly, this task is only for those who know how to solder and desolder
a PCB. If you are in doubt about doing this, then DON'T! You have more to
lose than to gain. If you know someone who is so skilled then ask them to
do it. I will accept no responsibility whatsoever for what losses you may
My REU worked perfectly right off the bat. If you follow instructions
exactly as I have outlined them, then your REU should work too. Good luck.
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