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Thread: My "new" Macintosh II

  1. #11
    Join Date
    Apr 2015
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    Austin, Texas
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    Quote Originally Posted by AdamAnt316 View Post

    The RAM slots. The second two SIMMs look different than the first two, or the last four. Not sure what's up with that.
    They're parity modules, a precursor to ECC memory.

    Parity memory modules have extra bits (hence the 9th RAM chip) in order to detect memory errors. 30 pin parity SIMMs are 9 bits wide instead of the usual 8 bits, with the extra being used in a calculation done by the memory controller to determine if incorrect data was sent over the bus. Parity checks aren't that useful, and can be a source of headaches because parity checks can only tell you an error happened, not precisely where it happened. It can also only detect single bit errors and can't correct the error on the fly like later ECC memory can. When parity checks are enabled on a PC and a parity error is encountered, you'll usually get the useless "Parity error, system halted." message and the computer won't boot.

    I'm pretty sure the Mac II doesn't support parity checking, so the parity modules are just running like normal memory modules.

    Quote Originally Posted by AdamAnt316 View Post
    What would be the best way to repair the traces? I haven't done much (if any) trace repair on a computer like this. Hoping the battery corrosion has only affected the top layer of traces; these multi-layer boards tend to make me worry.......... -Adam
    Scrape off the conformal coating on the traces with a small flat razor so any battery goo can't get stuck between the coating and the trace and cause continual damage. Once you scrape the coating off the traces, I'd recommend a rust inhibitor solution like Krud Kutter on a cuetip and rub it on the trace until it becomes a uniform copper color again. I would not recommend using vinegar because it is just as bad as battery goo, except it's an acid instead of a base. It will eat away the traces rather than combine with them to form something like copper sulfate or copper carbonate (the green corrosion on the traces.)

    If you find that the trace looks bad after you clean it, strip a long section of stranded copper wire and solder a few strands out of the bunch to one end of the exposed trace and route it along the length of damaged trace, cut it to length and solder as much as you can to the trace. If solder doesn't stick to the trace, try lightly sanding it with fine sand paper.

    After you're done, you can apply conformal coating to the area. If you can't get or find any, clear nail polish works.

  2. #12

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    Quote Originally Posted by GiGaBiTe View Post
    If solder doesn't stick to the trace, try lightly sanding it with fine sand paper.
    I think the finest you can find at walmart is 2000. Auto parts stores may stock finer stuff. But Testor's makes a pack of extremely fine sandpaper sheets. Craft or hobby stores have it. You can also just use some flux to clean the copper.

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