jason@cs.utexas.edu (Jason Levitt) (01/17/90)
Thanks to all that responded. The Macintosh II, it turns out, is a very early model. The motherboard does need to be replaced and Apple provides a replacement for free. The service techs claim that the boards are identified by inspection, not by serial numbers. Even thought the PMMU is an early mask, denoted by "XC", this does not appear to be a problem. Thanks to all that reponded. Here are some sample responses: > roadman@portia.stanford.edu I and two friends all have XC68851rc16 chips in our IIs without problems. I think it likely that your II motherboard could be exchanged at no cost if you do the footwork to get Apple and your dealer together. Almost for sure, your board has the A roms and those PALs which restrict memory on each nubus slot to 1Mbyte. Apple has in place a program through 1994 for no-cost mboard swaps for people who bought third party memory boards from Nat Semi and others. If calm discussion doesn't get the job done, find a dealer who seems to have lots of potential customers in the store and make a lot of noise. jtwarden@cmyharis.chem.rpi.edu Are you sure you have the PMMU seated all of the way into the socket and in the proper orientation? I had the same problem because the chip was seated properly. The PMMU should have the same orientation that the dummy chip had. Good luck. Frank Malczewski (malczews@nunki.usc.edu) Don't quite recall the specifics, but a number of the motherboards apparently went out that could not use the PMMU properly, as the circuitry had not been properly completed (some of the pins had no relevant connections to the motherboard). I believe that for these motherboards, Apple is replacing them essentially free of charge. I had little problem when I installed the PMMU having the same mask as yours. [Are you sure you aligned it in the socket properly?] jlee@watcsc.waterloo.edu I remember reading in a MacWeek [a Nov/Dec 1989 issue] about how someone at Apple acknowledged the fact that some early Mac II's [maybe including mine] will not work with an MC68881[sic?]. The reason was that the connector for the PMMU wasn't correctly connected to the rest of the board - a few missing solder connections or something like that. The only was to tell was to take a PMMU and try it out. I believe that Apple said they would replace the board. But CHECK IT OUT in case. Ted Goldstein du4@mace.cc.purdue.edu The problem is problem is probably in your Mac II motherboard. There was a little blurb in MacWeek a few weeks ago that said that a few thousand of the early MacII motherboards are incompatible with the PMMU. They also said that there is now way to tell from the serial numbers which Macs are effected, but dealers are authorized to replace motherboards for users who encounter the problem. John Unruh I have read that certain Mac II logic boards will not work properly with the PMMU chip. Apple has acknowledged the problem, knows the set of serial numbers that have the problem, and will repair/replace the boards. I suggest contacting a dealer and asking about it. Walt Dixon >From what I've seen, you have stumbled across a known problem with early MacIIs. It is my understanding that apple will fix the problem, but I have not seen this in writing from apple. ----- Jason Levitt P.O. Box 49860 Austin, Texas 78765 (512) 459-0055 Internet: jason@cs.utexas.edu | "Disneyland exemplifies the essence of UUCP : cs.utexas.edu!hackbox!jason | the American spirit and continues to BIX : jlevitt | show us the way to follow our dreams." | -Ronald Reagan [1990]