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Thread: Replacement for U32 chip (cassette basic)

  1. #1

    Default Replacement for U32 chip (cassette basic)

    In my '83 IBM 5150 the U32 chip was apparently corrupted or something because it gives me "FC00 ROM" error. I tried reseating the chip but it didn't make any difference.

    I tested that I could use U32 chip from my older '81 machine but I was wondering if I could erase and burn the faulty U32 again?

  2. #2
    Join Date
    May 2018
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    From what I can see its not a standard 27xx EPROM and so you need to an adapter to use a standard EPROM.
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  3. #3
    Join Date
    Apr 2010
    Albany, OR USA
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    Quote Originally Posted by musicforlife View Post
    .... I was wondering if I could erase and burn the faulty U32 again?
    I'm pretty sure those are OTP chips. Meaning One Time Programmable. They don't have a quartz window that would be used to erase the standard EPROM. Stands for Erasable Programmable Read Only Memory. Only erasable using UV light through the quartz window. The later EEPROM (Electronically Erasable Read Only Memory) could be erased electronically by the same device used for programming. You will need to use a new chip like Gary C mentioned.

  4. #4
    Join Date
    May 2006
    Melbourne, Australia


    IBM used the same ROM type, although manufacturer sometimes varied, for the Cassette BASIC chips (U29 to U32) and the BIOS chip (U33).

    Therefore, another replacement option is a programmed MCM68766, the MCM68766 (no adapter required) having been used in the past by others as a substitute for the BIOS chip. Example usage at [here].

    At least two people/companies at [here] can supply and program MCM68766's. If your U32 is labelled '5700043' or '5000023', then the code to be programmed into the MCM68766 is at [here]. The code for other versions of U32 should be on the Internet somewhere.


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