Xref: utzoo comp.sys.att:8343 unix-pc.general:4403 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!cs.utexas.edu!uunet!portal!cup.portal.com!thad From: thad@cup.portal.com (Thad P Floryan) Newsgroups: comp.sys.att,unix-pc.general Subject: UNIXPC Motherboard RAM upgrade, 512K to 1MB or 2MB Message-ID: <25476@cup.portal.com> Date: 29 Dec 89 10:02:08 GMT Organization: The Portal System (TM) Lines: 157 Lenny forwarded a question to me, and I responded privately. It seems it's time again to generate interest in upgrading the motherboard RAM on a UNIXPC, so I've edited out the private portions of my reply and am posting the following. Enjoy! .................... The implication from the message Lenny forwarded to me is that you wish to upgrade a 512K motherboard to be a 1MB motherboard (because you stated you had 36 256K DRAMs delivered by Santa! :-) The "usual" upgrade is to 2MB (72 DRAMs) as long as one is desoldering all the chips and inserting sockets. You will, in any case, have to remove 72 of the 64K DRAMs even if you want to install only 36 256K DRAMs. Before you even begin, please, PLEASE, ask yourself if your have the skills necessary to remove the existing DRAMs without damaging the motherboard. Several people in our Users' Group have already destroyed their motherboards because they DID NOT remove the old chips correctly. In all cases, the plated-thru hole "barrels" were lifted, causing separation of the traces in the INNER layers of the motherboard. Such damaged motherboards are NOT repairable. Replacement motherboards are available from Discovery Electronics or the AT&T San Leandro (CA) Repair Facility. If you feel confident about removing the old chips (three methods are described below in "quick" form), then the parts you need are: 1) one 74F258 NOTE THE "F"; no substitutions permitted. This part should cost no more than about 25-50 cents. 2) 72 machined-pin IC sockets. Augat preferred, and BE SURE they are the slim-profile so they can be placed side-by-side on the motherboard; one guy bought Augats that were a bit wider and would NOT fit side by side on the motherboard. You SHOULD install all 72 sockets even if you're only going to install 36 DRAM chips because you will have removed 72 64K DRAMs. Several other mfrs besides Augat also make machined-pin sockets; these sockets are the ones with the round holes on top with a "quality" look; DO NOT SUBSTITUTE the el cheapo sockets with the metal tab that contacts only part of the IC pins ... the trouble those sockets cause in the long run is just not worth the hassle. You will be spending approx. 12 hours to do the conversion, so spending a bit more for quality sockets (like the ones ALREADY in in the UNIXPC at other expensive IC locations) is a small price. You can, if you're adventurous, solder-in the new DRAMs and bypass sockets altogether, but ... :-) These sockets will have 16 pins to match the 256K DRAMs. 3) one small jumper wire, such as you can cut from a 1/4 W resistor end. Removing old DRAMs: Method 1: **PREFERRED** Get a desoldering tool such as OK SA-150 Vacuum Desoldering Station. These cost around $500-$600. The time one saves is phenomenal. Simply turn the motherboard upside down, put the tool on each DRAM pin, and pull the trigger. Do this to all 1152 pins. Each DRAM will simply fall out once its last pin is freed (assuming the motherboard is upside down!) and will be reusable in other systems. This method will probably take all of about 60-90 minutes depending how fast you can position the "gun" on each pin (figure 3-5 seconds per pin). Method 2: Get a SoldaPullit (spring-loaded, hand-operated solder sucker) and a good, hot, fine-tip soldering iron. Cock the SoldaPullit, heat an IC pin, wait 'til the solder melts and place the SoldaPullit quickly on the connection and press its trigger and hope all the solder gets sucked up. This procedure can take 15-30 seconds per pin, so figure on about 5-6 hours. Cocking the SoldaPullit will probably rub the skin off your hands down to the bone before you're through, so plan on spending several short sessions instead of a single all-nighter. This procedure also assumes the motherboard is upside down. Method 3: From the TOPSIDE of the motherboard, you can clip each pin from each DRAM, toss the non-reusable DRAMs in the garbage, then with tweezers and a soldering iron remove each pin one-by-one. Then with either a solder wick (like braided wire) or a SoldaPullit, and a soldering iron, clear the solder from each DRAM hole. Figure 12 hours for this method. CAVEAT! CAUTION! BEWARE! VORSICHT! ACHTUNG! PTOOIE! ARRGH! If you clip the DRAM pins the "wrong" way, you will destroy your motherboard. Now, the correct way (which I did ONCE, before I bought the OK SA-150) is to buy a pair of micro flush-cut diagonal cutting pliers (figure $30-$50 for a "proper" pair (and, no, such pliers are NOT available at Radio Shack)), you MUST clip the pins right at the point they enter the IC package, NOT AT THE POINT WHERE THE PINS GO INTO THE MOTHERBOARD. Even with flush-cutters, it's possible to "pull" the pins if you clip at the motherboard, and this will destroy the plated-thru holes as several people have already discovered. Example: _____ clip IC pin here +-----------+ / __| DRAM |/__ / | | \ | +-----------+ | ____________|____________________|______________motherboard Once all the 72 64K DRAMs (and pins if you used the "clip" method) are removed, insert the sockets into the motherboard and solder them in place. Look along the edges of your motherboard; you'll see reference designations as letters along one edge, and numbers along another edge (the front edge has the numbers). The DRAMs are in the region 2A to 10H. Locate position 13B on the motherboard (towards the center front edge). If there is NOT a 74F258 IC there, insert one (can be soldered directly into the motherboard). "Chances are" the resistor pack needed as pullups will already be in its location on the motherboard; at least, I've never seen a motherboard without one. Now, at position 12A, is a jumper JR1 which is really a board trace between positions E1 and E3; it needs (for a 256K DRAM motherboard) to be re-jumpered to connect E1 and E2. You do this using an Xacto knife and cutting the PC board trace between E1 and E3 and using a wire jumper to connect E1 to E2. I don't recall offhand whether the PC board trace is on the topside or the underside of the motherboard, but it's there and you may need a magnifying glass and good illumination to see it through the soldermask (the green junk). For a professional job, I also HIGHLY RECOMMEND you clip all the protruding pins from ALL the newly-installed IC sockets flush with the underside of the motherboard; there are special flush edge-cutting pliers for this kind of operation. If you DO do this, be sure to do it outside because all the little bits and pieces can get all over your table, floor, etc. And be SURE all the bits are pieces are blown off (with your breath and hands) before bringing the motherboard anywhere near your disassembled system; a stray particle can cause a short-circuit on the motherboard and/or other system components. Finally, install your DRAMs. Since you've only 1MB worth, use the back four rows (the front 4 rows of sockets will be empty until you get some more DRAMs). Each row has 9 columns' worth of DRAM sockets (one byte + parity). Reassemble your system, then run the memory tests from the Diagnostics disk for several hours to be sure all's OK. If you did all the mods correctly, everything should be fine. NOTE: I deliberately detailed only the methods and not the techniques of doing the mod. If you don't feel comfortable doing the mods and/or this is your first experience with soldering irons, I strongly urge you to contract a service technician to do the work for you. After seeing several people in the users' group hose their systems because they weren't methodical and were too over-eager, I have to urge you to be careful. The mods as outlined above have worked fine for me. BUT YOU DO THEM TO YOUR OWN SYSTEM AT YOUR OWN RISK. I HAVE CHECKED THE INSTRUCTIONS FOR TYPOS BUT CANNOT BE HELD RESPONSIBLE FOR ANY ERRORS. The above paragraph is to cover my ass, legally speaking. Frankly, the mod is quite straightforward and shouldn't present any untoward difficulties if you're not all thumbs. Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]