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Thread: Mac 128 gives Sad Mac - bad RAM?

  1. #1

    Default Mac 128 gives Sad Mac - bad RAM?

    Hello everyone. I picked up a Mac 128K last year which throws a Sad Mac code upon turn-on, along with little dots twinkling on the screen. The code under the Sad Mac is 042822. According to this page, it would seem to indicate that the unit has bad RAM chips at locations F6, F10, G8, and G10. What would be my next course of action? Also, where would I find the proper RAM chips for a 128K? Finally, is there a way to check and see if anything else is wrong? Thanks in advance!
    -Adam

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    Quote Originally Posted by AdamAnt316 View Post
    Also, where would I find the proper RAM chips for a 128K?
    They are 64-kilobit DRAMs, the 4264. Two rows gives you 128K. Same thing used in the Apple IIe, and other computers of the era.
    Last edited by DFinnigan; August 3rd, 2018 at 12:16 PM. Reason: 4264

  3. #3

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    Quote Originally Posted by DFinnigan View Post
    They are 64-kilobit DRAMs, the 4164. Two rows gives you 128K. Same thing used in the Apple IIe, and other computers of the era.
    Thanks for the reply. I wasn't sure if there was a difference between the 4164 and the 4264s said to have been used in these early Macs. Is replacing the RAM chips likely to solve my problem, or could there still be something else wrong? Again, thanks!
    -Adam

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    In my experience, bad DRAM is a very common problem with the 128K macs, and I'm guessing that since you have a working display, replacing the DRAM should resolve that issue. Stuck floppy drives are also a common problem, so while you have it apart to replace the bad chips, you should clean lube the floppy mechanical mechanism.

    Keep in mind that it's a 4 layer board so power and ground pins take a lot of heat (not temperature) to extract the pins. Make sure you know what you are doing before replacing chips.

    regards,
    Mike Willegal

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    Quote Originally Posted by AdamAnt316 View Post
    Thanks for the reply. I wasn't sure if there was a difference between the 4164 and the 4264s said to have been used in these early Macs.
    It's the 4264. I said the wrong thing in my post above. I'll correct that.

  6. #6

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    Quote Originally Posted by mwillegal View Post
    In my experience, bad DRAM is a very common problem with the 128K macs, and I'm guessing that since you have a working display, replacing the DRAM should resolve that issue. Stuck floppy drives are also a common problem, so while you have it apart to replace the bad chips, you should clean lube the floppy mechanical mechanism.

    Keep in mind that it's a 4 layer board so power and ground pins take a lot of heat (not temperature) to extract the pins. Make sure you know what you are doing before replacing chips.

    regards,
    Mike Willegal
    Thanks for the reply. Should I replace all of the DRAMs, or just the ones indicated by the Sad Mac code? What does it mean that the memory chips in question failed the "Mod3 test", anyway? With regards to the floppy drive, what procedures are recommended for lubrication? I have an external 400K drive which seems to be partially seized up, as it immediately ejects any disk put into it.

    And thank you for pointing out the multi-layer board issue, as that was another of my concerns. Are there any special tools or procedures I should use? My general go-to with regards to desoldering has been braid, a'la "Soder Wick". Would this be sufficient, or should I use a vacuum-based desolderer or somesuch? Most of the circuit boards I've worked on thus far have been single- or double-layer boards.

    Quote Originally Posted by DFinnigan View Post
    It's the 4264. I said the wrong thing in my post above. I'll correct that.
    Thanks for the clarification. What is the difference between the 4264 and 4164, anyway? Can 4164s be used in this application? Is there a good source for either type of RAM chip?
    -Adam

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    Quote Originally Posted by AdamAnt316 View Post
    Thanks for the reply. Should I replace all of the DRAMs, or just the ones indicated by the Sad Mac code?
    I would order 16 replacement 4264 DRAMs. First replace only the ones indicated by the error. Then if there is still a Sad Mac, you can replace more if need be.

    What does it mean that the memory chips in question failed the "Mod3 test", anyway?
    The Mac's memory test writes certain bit patterns and reads them back to verify. There is more than one test. Mod3 is one of them.

    With regards to the floppy drive, what procedures are recommended for lubrication? I have an external 400K drive which seems to be partially seized up, as it immediately ejects any disk put into it.
    I recently restored my 400K Sony drive, and wrote this article about it: Fixing the 400K Disk Drives. Try using white lithium grease.


    What is the difference between the 4264 and 4164, anyway? Can 4164s be used in this application?
    They are very similar. The same part number 4264 ended up being used for a different type of 64k DRAM by a different manufacturer. I would recommend sticking with MT4264.

    Basically, you want a DRAM that has 16 pins and is 64k x 1 bit.
    Last edited by DFinnigan; August 4th, 2018 at 07:59 AM.

  8. #8
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    If you're extra adventurous, you can use 41256 memory chips and perform a slight modification to the motherboard to bump the memory from 128k to 512k. It makes the machine much more usable, though you'll have purist collectors screaming bloody murder at you for doing it.

    If you don't want to perform such a mod, I'd recommend at bare minimum removing all memory chips and replacing them with sockets because 30+ year old memory is on borrowed time.

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    Quote Originally Posted by GiGaBiTe View Post
    If you're extra adventurous, you can use 41256 memory chips and perform a slight modification to the motherboard to bump the memory from 128k to 512k.
    Depending on which motherboard revision you have, you may need only put 256 kilobit chips in. Does the copyright date read 1983 or 1984 on your motherboard? The 1984 one is the same for both 128K and 512K of RAM-- only difference is 64 versus 256 kilobit chips

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