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 other functions.

     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 housing.

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 I.

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 Bank II.

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 incur.

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.
