The following information outlines the steps necessary to change the Commodore 1700 RAM expansion unit into the 1750 unit. In other words, you will have 512K capabilities. PLEASE read through the instructions carefully BEFORE doing anything!!
You will need the following materials:
Soldering Iron (pencil type)
Electronics-grade solder
Desoldering Tool (or wick)
Sixteen 16-pin I.C. Sockets
Sixteen 150ns or 120ns 256K Dynamic Ram chips
The I.C. Sockets are not required, but recommended, to protect the new RAM chips from excessive heat when installing. They cost about $0.15 each, so well worth the small investment.
The Dynamic RAM chips can be either 150 or 120 NanoSecond-types. The 150ns should run around $2.98-$3.50 each. Shop around for a good price. Most Electronics stores carry them. They are abreviated as DRAMS, in case you were wondering. The 120ns are more expensive. Make sure that you acquire chips that are all from the same manufacturer, and if possible, all from the same batch.
Once all the materials are gathered, pry open the plastic casing of the 1700. It is attached in four places, and should slide straight up and off the base of the unit. It is not glued or clipped.
Now to open the metal shielding. It is attached on the two sides, and hinged in the back. Pry the shielding away from the board on both sides and carefully lift up and back, towards the rear of the unit, being certain not not break the metal where it is hinged in the rear.
Upon inspecting the board, you should see one large chip towards the front and labeled 'MOS'. This chip is very susceptable to static electricity and should be avoided if you have little experience in board-work. If you know what you're doing, remove the MOS carefully from its socket and place it in a non-conductive pad, pins-first. (If it isnt in a socket, do not remove it).
Now look in the rear area of the board. You should see 16 smaller chips, labeled U1 thru U17 (on the board itself). These will be the chips (DRAMS) you are replacing.
Now look in the front area of the board. You should see two sets of flat pads. They are labeled J1 and J2. You are only concerned with J1. After you replace the DRAMS, you will need to cut the tracer that connects the two pads on J1.
Let's get started. Lift the board out of the plastic base, and off of the metal shielding. Place it on a non-conductive surface. While performing the next steps, stay clear of the MOS chip!
Using your soldering iron (NOT a high output GUN!), and your desoldering tool or wick, remove all 16 DRAMS from the board. This is the hardest task you will be performing in this operation. Make sure you do not inadvertantly desolder or overheat any of the resistors or other components that are nearby.
After all the DRAMS are removed, ensure that the holes are free of obstructions (like excess solder). Use the iron and a toothpick to open the holes, if obstructed. Now, place the sixteen 16-pin I.C. sockets where you just removed the DRAMS, and solder them in place using an apropriate electronics-grade solder.
When all sockets are installed, place one 256K DRAM on top of each socket, making sure the pins are straight, and snap each DRAM into its socket.
Now, using a sharp knife, cut the tracer that connects the two pads on the jumper named J1. It is hard to see, but make sure it is cut and that the two pads are no longer connected.
Almost finished. Place the board carefully back into the plastic base, and on top of the metal shielding. Fold down the shielding and re-attach it to the base. Place upper section of plastic shell back on top of unit, and slide it down until snug.
Now, place the 'new' unit into your 128 and run the RAM TEST program that came with the 1700. You should see that the the program returns a 'SIZE=512K' message when it is running, and that no errors exist while testing the unit.
If you do get an error in one of the banks, recheck your work and ensure all the connections are firmly soldered and that no extraneous solder has been inadvertantly thrown onto some other component. If you still get errors, you may have damaged another component on the board, or you may have bought a bad DRAM. At this point, the only alternative is to bring it in for a service-person to check out, or if you are adept at this sort of thing, find out which component is at fault.
If you are a novice, I would not suggest changing your 1700 to a 1750-clone by yourself, as it is easy to damage the MOS, new DRAMS, and other components. I fully take no responsibility for damaged units, doctor bills arising from slamming your head against a wall, or lost dogs. <huh??>.
This information was passed on to me by Kevin Stevens (KeS), who recieved it from Mr. Bob Carpenter. It has worked on our units with no trouble at all. It took Bob about an hour or two to accomplish, Kevin about 6-8 hours, and myself about 4 hours. Your mileage may vary.
