O.K., here's the thing ... I have a 128k that sounds like it had exactly the same upgrade yours did. Though, it sounds like yours went a step further and added the Plus ROMs to make it a 512ke. -- not sure where your extra circuit board went though -- it's also possible that it was upgrade past 512k of RAM and the add-on board was designed for that purpose. I have a "tiny" circuit board (raised on pins so it sits just above the 68000 chip) with ONE chip in a socket marked: 74F253 PC 11445, and a 2.2k ohm resistor that sits at right end of the 68000 chip (see pic below -- where is yours). But it doesn't replace anything, it was added to the 128k board in the only open leads on the board (which was originally designed for 512k in the first place). I find the following picture extremely helpful in talking about the logicboard mods as there were so many different 3rd party hacks that done:
digibarn ANYWAY, I don't think the logicboard mods are your problem. I have 2 128ks and a 512k all but one of the 128ks has been modified and all of the modified boards work in my "good" 128k chassis. The other 128k and 512k exhibit different problems, one is the exact checkerboard pattern you describe without a startup "chime". The other does nothing and starts to smell like burning electronics and "chime" a lot if I don't turn it off. As I said, the logicboards have nothing to do with the problem. I would say your problem is with the Analog boards which were notoriously plagued with problems. If something goes in a compact Mac, it's not likely to be the logicboard, even if it has an "unofficial" mod (Apple did not condone these 3rd party solutions -- they would just as soon swap your logicboard and charge you twice as much or more). Anyway, I don't have all the links at my fingertips, so I'll just tell you that you can do a search online for analog board repairs (there are two or three excellent sites), which eventually I'm going to visit myself so I can get these old boxes back in service. BTW -- my "good" 128k exhibits symptoms of the checkerboard screen if I turn it of and on too fast. Fortunately a slow power-off returns everything to normal. So I imagine this is a harbinger of things to come, so I'll be looking up the sites myself and post them when I do. Oh, also, the 1256-15 chips: where do you get them? I've been toying with experimenting with an upgrade to see how far I can take the RAM in those sockets -- obviously when they de-soldered the original 128k RAM they put those sockets in for an upgrade or they would have just re-soldered the 512k RAM directly to the board. Also, what is the difference between the 1256-15 and -12, -10, 64-12 chips? If it is actual RAM capacity, then they may not work with the resistor board that's been added to provide the additional power for the added RAM tailored for the -15 chips. Good luck. > From: "Edwin P. Groot" <[EMAIL PROTECTED]> > Reply-To: "Compact Macs" <[email protected]> > Date: Sun, 20 Mar 2005 11:03:16 +0100 > To: "Compact Macs" <[email protected]> > Subject: Fat Mac Won't POST > > Hello all, this is my first post as I'm new to the list. > I found in the trash a fat Mac that gives a checkerboard pattern when > the power is applied. There is no startup tone audible. The pattern is > about 15 squares wide and 40 squares high. Any ideas on repairing the > problem (besides buying a Macintosh 128 logic board)? -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[email protected]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---------------------------------------------------------------
