AOH :: REU1700.TXT|
Upgrading a Commodore 1700 REU to 512k
This file gives instructions for modifying a Commodore 1700 REU to expand
the memory to 512K (equivalent to a 1750). Be aware that this modification
is not supported by Commodore, and if you try it you will definitely void
your warranty. This is not for someone who's never soldered or de-soldered
before, either, so be warned. You will need 16 256K RAM chips (41264) and
sockets for them. You should use 120nS chips if at all possible.
First, find a good, well-lighted workspace. This job takes time, and you
want to make sure you can leave the REU in a safe place if you don't finish
it all in one sitting. Be sure you can ground yourself easily, because IC
chips are extremely sensitive to static. Take all possible precautions
against static discharge.
Open the case of the REU by gently prying it apart. Carefully remove the
circuit board in its metal RF screen. Open the screen and remove the
circuit board. Be sure to ground yourself well (this can't be emphasized
enough; one little spark and you may lose the whole project). Be very
careful around the large IC on the board near the connector.
The next step is to de-solder and remove the 16 64Kx1 RAM chips. (Take
note of where "pin 1" on these chips goes, so that you can install the new
ones with the same orientation.) Do this with a minimum of heat, so as not
to damage the chips. If you are using a spring-loaded "solder sucker" be
SURE to ground yourself often.
When those chips are all out, install the sockets for the new chips. This
may seem like a tedious extra task, but it is worth every minute of your
time. Sockets are a lot easier to install than chips are, and you don't
have to worry quite so much about excessive heat on a socket. Once the
sockets are in place, install the new chips, being sure that the "pin 1"
orientation is correct.
Next, cut the trace on the circuit board that is marked "512K cut." Then
you should use a meter to check for a power-to-ground short. The impedance
between "+5" and "ground" should be about 7-15 ohms.
Carefully put the unit back together, making sure all the parts are back in
position. Make sure your computer is OFF, install the REU, and then turn
the computer on. You should be able to run the RAMTEST program that comes
with the REU at this point, and it should show you that the new memory is
operating. If you've done your work carefully, all should be well. If
your unit isn't working right, check all your solder joints carefully and
make sure you haven't bent any of the pins on any of the IC's when you
installed them in their sockets. This is a common cause of problems. If
you've bent a pin, you should be able to bend it back into place, but those
pins will not bend any more without breaking off, so work carefully.
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