beth@sphinx.UChicago.UUCP (Beth Christy) (07/16/85)
[This is being posted for a friend. Replies should be directed to Jerry Callen, ..!ihnp4!gargoyle!sphinx!zort] ------------------------------------------------------------------------ There seems to be some confusion in netland about do-it-yourself 512K Mac upgrades. I've done 4 of them now (3 "old" boards, 1 "new" board), so I feel somewhat qualified to talk about them. Here's everything you ever wanted to know about doing it yourself: 1) Some bozo started a rumour that the Mac logic board is soldered with "pure aluminum". HOGWASH! For the last time, the Mac logic board is your standard, plain-vanilla 4 layer PC board. THERE IS NOTHING MAGICAL ABOUT THE MAC LOGIC BOARD (except perhaps Burrell Smith's design job...)!!! 2) If you plan to do the upgrade, get the January 1985 issue of Dr. Dobbs Journal. It has a very complete article on how-to-do-it. There is an error in the text of the article - in the discussion about mounting the "piggyback" multiplexor socket, it says that pins 1,7,14 and 16 will be soldered to the chip below. This is wrong - they mean pins 1,<<8>>,14 and 16. The drawing later on in the article that shows the wiring diagram for the piggyback socket IS CORRECT! 3) The job is easiest with two people. I get the person whose Mac I am upgrading to be the helper. After clipping the leads on the old 64K chips, clamp the board vertically. One person applies heat to the back of the board, while the other pulls the pins from the component side of the board. The "puller" should wait until the solder melts (it's clearly visible when this happens) before grasping the the pin and quickly pulling it free of the board. When doing pins 8 and 16 (the power and ground plane pins) it is important to get the pin on the first pull - if it goes halfway and hangs up, it's harder to get on subsequent tries. Once all the pins are clear, the holes have to be cleaned. Again, one person heats the back of the board, and the other uses a solder sucker from the component side. 4) Make certain that you clean up any splatter from the solder sucking. If you spray the board with a degreasing spray, you can clearly spot any splatter. 5) When soldering in the chip sockets (and DO INSTALL SOCKETS!), use only the smallest amount of solder necessary to get a solid connection. It's easy to apply too much solder, and thereby cause shorts on the component side of the board, UNDER the sockets, where you can't see them. If this happens, you may have to cut out all the sockets to find the short (a drag, to say the least...). 6) Do the chips a row (8) at a time. Install the new RAMs in the row, put the board in the Mac and power it up. This way you can limit the number of checks you have to do to find a problem. 7) The Dr. Dobbs article has pretty comprehensive "debugging" info. Make sure you have a VOM handy. I found that having one fine-tipped test probe and one micro-clip probe (to clip to IC pins) is useful. The only problem I've run into is shorts (caused by bad soldering technique). If your Mac displays garbage when you power up, DON'T PANIC! This happened on 2 of the 4 upgrades I did, and in both cases I was able to find the problem without too much trouble (though in one case I had to cut out a row of sockets). What I've learned from this is to either a) do the soldering myself, or b) if you let the assistant solder, WATCH CLOSELY. I sort of feel that the person whose Mac is being upgraded should be allowed to do as much of the work as possible - but I've gotten a bit shy about letting them do the soldering (both of the "problem Macs" were soldered by the helper...). 8) The price for 150ns 256K DRAMs is now under $4/chip, so you can easily do the job for under $100. Microprocessors Unlimited seems to have consistently good prices on the chips - look in Byte for their ad. (I have no connection with them other than as a customer). I hope this helps. I am so furious about the price of the upgrade - I sort of feel that each Mac I do is a blow for truth, beauty and the rights of "the little guy" (Yeah, pretty sappy, I know...). One last warning - DON'T EVEN THINK ABOUT DOING THIS UPGRADE AS YOUR FIRST ELECTRONICS PROJECT! It isn't all that hard, but you MUST have good soldering technique and not be freaked out if you have problems. I also wouldn't do it on a Mac that was still in the warrantee period, but that's my own problem, I suppose. GOOD LUCK! Jerry Callen Mailnet: Systems.JLC@UChicago.Mailnet BITNET: Syszort@UChiMVS1 USnail: 5615 S. Woodlawn, Chicago, IL 60637 ------------------------------------------------------------------------