When a Macintosh Plus hangs on boot, check for a connected SCSI device that is powered off. If such a device is connected, the Macintosh Plus may have the original 128K ROMs that have this problem, which was corrected in the revised ROMs.
Workaround:
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Power up the SCSI device or disconnect it.
There are two methods that can be used to check the ROM version on a Macintosh Plus: the serial number and the built-in mini-monitor.
1. Serial number
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A factory built Macintosh Plus computer with a serial number beyond F609xxxMxxxxx has the revised ROMs. However, if you are not sure if your machine was upgraded to a Macintosh Plus, or if you have a serial number earlier than that, move on to the next method.
2. Mini-monitor
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Follow these steps to use the mini-monitor to check ROM version:
Step 1
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Press the interrupt switch on the programmer's switch to enter
the built-in mini-monitor.
Step 2
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Type DM 400000. If the third byte value displayed is EA, it means the revised ROMs; if it's EE, it means the original 128K ROMs.
Step 3
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C. Type G to return.
ALL upgrade kits were shipped with the revised ROMs.
Article Change History:
23 Aug 1995 - Removed extraneous information and reformatted.
22 Jul 1992 - Reviewed.
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