src@cs.odu.edu (Scott R. Chilcote) (09/27/89)
Hi! I just got done upgrading a 2-chip ROM Mega 2 ST to TOS 1.4 using a
six-chip PROM set from Atari. The source of this upgrade was Lyco in
Woodbridge, Virginia. If you are interested in upgrading from a two-chip ROM
set to a six chip set, here's how I did it.
I'd better add a disclaimer at this point. The following is merely a
description of something I did to my computer. How you use this information is
up to you.
With that said...
First, I removed the motherboard from my Mega. I also removed the floppy
drive and the power supply -- it makes the board much easier to handle. I was
careful to observe static electricity minimization, since some of these chips
contain MOSFET devices.
I noticed that my Mega had no sockets for the four ROM chips that had not
been installed; not only that, but the holes were all soldered closed! The
first thing I had to do was use a solder-sucker and some desoldering braid to
carefully open the closed holes for U3, U4, U6, and U7. It took great care not
to scratch the ultra-fine traces that run around and between the solder pads.
Next, I installed the sockets. I inspected each solder joint with a
magnifying glass to look for solder bridges and cold solder joints at each pad.
It was then time to move the two jumpers marked 'w2' and 'w3' on the
motherboard. At the front of the Mega's motherboard, right next to the MMU
chip, there are two small jumpers that look exactly like resistors (or at least
they did in my Mega). They are marked with a single black band -- perhaps to
signify zero ohms? Whatever the case, they are labeled with small white boxes
on the board's silk print, with holes 1 and 3 marked on each. The jumpers were
installed in holes 2 and 3 in both cases. These two jumpers had to be
desoldered and moved to holes 1 and 2. If I'd been careful, I could have just
desoldered the wire in hole 3 and moved it to hole 1... Now that I think about
it.
Another jumper, which was not already present, had to be installed in a
nearby box labeled 'w4'. This box is clearly marked on the motherboard
inbetween U12 and U24. I used a lead clipped from a spare resistor, about 1"
long for this; any fine bit of wire would have done. It was stiff and so did
not need to be insulated from surrounding metal.
I saved the most difficult part for last. The final step was to remove an
integrated circuit entirely from the Mega's motherboard. This chip is labeled
U12, and its only purpose is to take the ROM signals that would normally
activate six separate chips, and funnel them (through the use of a three-input
AND gate) into the two-chip ROM set. Since I needed to use all six ROM chips,
this IC had to be removed. It was difficult for me because the desoldering
braid did not remove all of the solder, and my solder-sucker couldn't vacuum
enough of it out. It took some severe wheedling to finally get this guy loose.
Of course, I had to remove the existing pair of ROMs and put the new chips
into the proper sockets. This took a bit of doing in itself, since the ROMs
are labeled with the proper numbers for the 520 and 1040 STs, but _not_ for
the Mega ST. I had to match up the chip designations instead. This is the
table I came up with:
520 ST Designation Mega ST
---------------------------------
U2 Hi-2 U3
U5 Lo-2 U4
U3 Hi-1 U6
U6 Lo-1 U7
U4 Hi-0 U9
U7 Lo-0 U10
After plugging the ROMs -- which are actually EPROMs with labels stuck over
their glass lenses -- into my Mega, I plugged 'er in and booted. The system
works perfectly, or as close as TOS 1.4 gets (pretty close)! I am using it and
TEMPUS II to write this file, and will be using it to upload it as well. The
improvement in FAT searching is worth the price, by itself! Other features
have also proven handy, including the keyboard cold-start.
Wether you have TOS 1.4 professionally istalled or choose to do it
yourself, I can heartily recommend the upgrade.
--
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|| Usenet: src@xanth.UUCP || ||
|| Arpa: src@xanth.cs.odu.edu || Q: Why did the chicken cross the ||
|| Earth: Scott R. Chilcote || Moebus Strip? ||
|| || ||
|| ||| "Sure, Jack, we || A: To get to... er... umm... ||
|| ||| trust you. But will || ||
|| / | \ will you respect us || -----=====#####=====----- ||
|| / | \ in the morning?" || ||
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'---------------------------------------------------------------------------'woody@heisenberg.lehigh.edu (robert "woody" woodburn) (09/27/89)
test. this is a test.
jeff@quark.WV.TEK.COM (Jeff Beadles) (09/28/89)
In article <10035@xanth.cs.odu.edu> src@cs.odu.edu (Scott R. Chilcote) writes: > > I saved the most difficult part for last. The final step was to remove an >integrated circuit entirely from the Mega's motherboard. This chip is labeled >U12, and its only purpose is to take the ROM signals that would normally >activate six separate chips, and funnel them (through the use of a three-input >AND gate) into the two-chip ROM set. Since I needed to use all six ROM chips, >this IC had to be removed. It was difficult for me because the desoldering >braid did not remove all of the solder, and my solder-sucker couldn't vacuum >enough of it out. It took some severe wheedling to finally get this guy loose. Well, I have a MUCH easier way to remove soldered-in chips. (As long as you don't plan to re-use them.) Go out and buy a pair of diagional cutters, with a fine (small) tip. (micro-sized) When the chip is sitting in the board, cut each of the leads where they go into the silicon. Then, just pick out the "body" of the chip. Then, get a pair of small needle nose pliers (or I usually use tweezers) and pull each lead out one at a time as you touch the pad with a hot soldering iron. Then, use solder wick to clean out the holes. I have yet to destroy a printed circut run using this procedure. You might want to practice once or twice on a junk circut board. Of course, if you decide to accept this way of removing IC's, you're on your own. I won't charge you a dime, nor will I accept any responsibility if you melt-down your ST. If you've got questions about this, drop me a note. -Jeff -- Jeff Beadles Utek Engineering, Tektronix Inc. jeff@quark.WV.TEK.COM uunet!tektronix!quark.wv.tek.com!jeff
adw3345@ultb.UUCP (A.D. Williams) (09/29/89)
Someone mentioned that Lyco was located in Woodbridge, Virginia.
I Beleive what they were referring to was L & Y Electronics, one of the
biggest Atari dealers I know of. The owners, John and Suzy (It's a mom &
pop operation) have almost everything and were installing 16 mz upgrades
the last time I was there.
Here's a plug for L & Y Electronics. Note that I am in no way affilated
with L & Y except as being a happy and frequent customer.
L & Y Electronics
13664 Jefferson Davis Highway
Woodbridge, Va. 22191
(703) 494-3444
Give 'em a call today!
Derrick Williams
Roch. Inst of
Technology.
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