tmiller@chaos.cs.brandeis.edu (Todd Miller) (05/04/91)
Professional 350/380 memory upgrade: Here is a how to guide for memory upgrade of the PRO 350 at home. At $2.00 per chip $64 will get you a 1 Megabyte of memory on your PRO and free up 1 expansion slot if you remove the memory board. Each board goes from 128K -> 512K and you could do 1 or both in the PRO. special thanks to Glenn Toczko, Hacker Extraodinaire Yours, Todd M. Miller Professional 350 Daughter Board Memory Upgrade The Professional 350 (PRO 350) requires 512Kbytes of memory in order to start P/OS. In the least costly configuration this requirement is supplied by two 128Kbyte daughter boards located on the motherboard underneath the hard disks. These boards are elevated above the motherboard on spacers and are easily recognized. An expansion slot usually holds another memory Board with an additional 256Kbytes. Together these boards form the 512kbytes of memory needed in the minimal system configuration. Because of advances in memory chips and DEC's useful fore-sight it is possible to install 1024Kbytes using only the two daughter boards. This may free up a slot or just give you additional memory. This file describes one method used to upgrade the memory boards. The upgrade requires 32 256K X 1 dynamic refresh memory chips with at least 150ns access time. The original chips are not in sockets so they have to be desoldered. To make desoldering simple we used the following technique. 1) Remove the memory boards from the PRO. 2) Pre-heat a burner on an electric range to about medium heat. 3) Get your pliers or an IC extractor ready. 4) Each board has 2 rows of 8 chips each. The chips will be removed 1 column at a time (2 in each column). Hold the board so that a column of chips is over the hottest part of the burner. When the solder his hot enough simply pull the column of 2 chips out. 5) Remove the board from over the burner an allow it time to cool. If you try to do too many columns at one time you will scorch the board. Minor scorching may be expected depending on the amount of patience you have concerning getting the burner temperature correct and how many rows you attempt to do at one time. If you are careful enough you should be able to do it without scorching the board at all! Any time you touch the board to the burner you can expect scorch marks. Note: Sometimes the pins on the old memory chips are bent outwards on the bottom of the memory board. This makes them harder to remove. Straighten them if you can. Note: Don't worry about the capacitors, they may fall out when the solder is molten. The can be replaced when the new chips are inserted. 6) After you have done all columns and removed all the old memory chips you still have to remove old solder. Our homebrew method of doing this is to use a vacuum cleaner as a solder sucker device. Turn the vacuum cleaner on and hold the nozzle between your knees. Using a soldering iron heat the solder on the pin hole a few inches away from the vacuum cleaner nozzle. When the solder is molten bring the board down on the nozzle so that the nozzle is centered under the hole. This sucks the solder out but it has a tendency to splatter it on the underside of the board too. 7) Use the soldering iron to collect the splattered solder into the pin holes on the other side of the board and then re-heat the pin hole and do step 6 again. After about three times the pin holes are clear from old solder. It could take longer for the first board until the technique is developed. Note: Solder will accumulate on the inside of the vacuum cleaner nozzle. I isn't very much solder but someone's wife could get mad about it. We don't know what will happen if the nozzle is made from plastic instead of metal as it was here. Perhaps some aluminum foil wrapped around the nozzle would solve both problems. 8) After steps 6 and 7 you should have a board with all the all the pin holes free of solder so that you can insert the new memory chips. Certain holes which are part of large traces are take more effort to unsolder because there is more solder in them. All holes need to be open in order to insert the new memory chips. Do the capacitor holes as well if necessary. 9) Place the new memory chips in the old holes and solder them in. Make sure they face the same way as the originals. You need only solder the chips from the bottom of the board, the plate-through holes will do the rest. 10) There are two jumpers that need to be soldered to enable the extra memory. They are labeled J1 and J2 on the board. Cut a piece of wire, strip the ends and solder the ends across the jumpers. 11) Reinstall the board into the PRO. 12) The P/OS toolkit ``show memory'' command should show 512K WORDS (1024K bytes) of memory with only the two mother boards installed. We have upgraded four boards this way so far and not one has failed so far. All the memory chips we used were tested in another computer (one with sockets) before they were installed. You may want to solder sockets into your memory board instead of the chips themselves. If you have bad memory when you start up your PRO it would be much easier to replace a socketed memory chip than a soldered one. Although we have singe'd a few boards perfecting this method the damage was only cosmetic. Removing the memory chips over the burner is the most difficult part of the operation.
chaim@eniac.seas.upenn.edu (Chaim Dworkin) (05/09/91)
Thanks to Todd Miller for posting that description of how to add memory to a Pro-350. I saved it for future reference. I currently have a Pro-380 with three additional memory boards in the cage. I wonder though if all that memory is necessary. Before I added the extra two boards I never ran out of memory and never had a program crash for possible memory reasons. Is there any application that requires more than the standard base memory? Chaim -- Chaim Dworkin (chaim@eniac.seas.upenn.edu)
mcculley@alien.enet.dec.com (05/10/91)
In article <42829@netnews.upenn.edu>, chaim@eniac.seas.upenn.edu (Chaim Dworkin) writes... >[...] I wonder though if all >that memory is necessary. Before I added the extra two boards I never >ran out of memory and never had a program crash for possible memory >reasons. Is there any application that requires more than the standard >base memory? The biggest effect of insufficient RAM will be excess swapping. You should seldom see anything crash or lock up from inadequate memory size, but you could see performance go down drastically. Depending on your applications there might or might not be a point at which adding more memory doesn't matter, but it's tough to tell. If you don't have any reason not to plug it in, why chance it? I forget exactly what the standard base memory was, but I think I can say authoritatively that it was expected to be adequate to meet normal application requirements. The question should be phrased "do any applications benefit from more than the standard (minimum) memory?" not "do any applications require more than the standard?" ^^^^^^^ (Answer is, depends on your applications, your mileage may vary...) - Bruce McCulley