Usually when one turns on their Macintosh, it smiles at them (Happy Mac). However, one day it may snarl at you. First lets explain what happens the moment you flick the switch, or hit the power key, inside your Macintosh.
Once your Macintosh is brought up to full power the Mac runs what's called in the computer world a Power On Self Test (POST). Several memory and system diagnostic tests take place. If any one of these tests fails, the Sad Macintosh icon appears. The Macintosh will display two 8-digit hexadecimal numbers displayed under the icon.
How do I make a Sad Mac happy again?
Most hardware failures that display a Sad Macintosh error will do so before the floppy drive or hard drive start spinning. If a Sad Macintosh appears after the disk starts spinning, the first digits of the error code are usually 'OF' and often indicate corrupted software. If you get this error code, try restarting the Macintosh with the Option and Command keys held down to rebuild the desktop file. You also may be able to fix these problems by reinstalling system software or disabling the extensions by holding down the shift key.
If all else fails it means there is a problem with the hardware and you should take your Mac to an Apple Qualified technician. Remember, attempting repairs yourself will void Apple's warranty. If you've never seen a Sad Mac before and you have this urge, try hitting the interrupt button (plastic things on the side of compact Macs, little buttons on the front of newer Macs, or some weird keyboard combination on others) while the Mac is checking the RAM (this is when the screen is gray and void of all else at start up). Of course, I'm not recommending it to anybody because I'm sure there is some way it might affect something adversely.
Sad Mac Error Codes On the original ROMs (128k, 512k, 512ke, Plus):
When you press the interrupt button on the side of your Macintosh when booting, you should get a sad Mac icon with '0F000D' and some bits cycling under the icon indicating it is performing a memory test.
This numeric code is in two parts: the first two characters are the class code and the second four are the sub code. The class code tells what part of the diagnostic program found the error and the sub class code tells what the error was. In the case of a bad RAM chip, the sub class identifies the bad chip.
The Sad Mac error codes have been changed to incorporate additional power for testing and to support the 32-bit world. Generally, the same codes are used for 68000 exceptions as with other Macintosh's, however they are displayed differently.
The traditional Macintosh error codes are displayed like this:
 
Where ΓÇ£FΓÇ¥ indicates an exception occurred, and ΓÇ£3ΓÇ¥ indicates an illegal instruction occurred. On the Macintosh SE and II, the display would appear:
 
Please note that 00000003 is a hex number.
The new powerΓÇôon error codes have the following format:
 
Where XXXX is internal test manager state information (ignore this), YYYY contains codes that indicate either an exception code, or the test number for a power on test failure. The ZZZZZZZZ code contains additional failure information to help track down the problem.
YYYY Error Codes:
$0001 The ROM checksum test failed. Ignore the Z field.
$0002 The first small chunk of RAM to be tested failed. The Z
field indicates which RAM Bit(s) failed. This small
chunk of RAM is always in Bank B.
Example: $AABBCCDD
AA=8 bit mask for bits 31-24
BB=8 bit mask for bits 23-16
CC=8 bit mask for bits 15-8
DD=8 bit mask for bits 7-0
$0003 The RAM test failed while testing bank B, after passing
the chunk tested for code $0002. The Z field indicates
which bits failed as in code $0002.
$0004 The RAM test failed while testing bank A. The Z field
indicates which bits failed as in code $0002.
$0005 The RAM External addressing test failed. The Z field
indicates a failed address line.
$0006 Unable to properly address the VIA1 chip. The Z field
is not applicable.
$0007 Unable to properly address the VIA2 chip (Macintosh II
only). The Z field is not applicable.
$0008 Unable to properly access the Front Desk Bus. The Z
field is not applicable.
$0009 Unable to properly access the MMU. The Z field is not
applicable.
$000A Unable to properly access NuBus. The Z field is not
applicable.
$000B Unable to properly access the SCSI Chip. The Z field is
not applicable.
$000C Unable to properly access the IWM chip. The Z field is
not applicable.
$000D Unable to properly access the SCC Chip. The Z field is
not applicable.
$000E Failed Data Bus test. The Z field indicated the bad
bit(s) as a 32-bit mask for bits 0-31. This may
indicate either a bad SIMM or data bus failure.
$000F Reserved for Macintosh compatibility.
$FFxx A 680xx exception occurred during power on testing. The
xx indicates the exception:
$01 ΓÇö Bus Error
$02 ΓÇö Address Error
$03 ΓÇö Illegal Instruction Error
$04 ΓÇö Zero Divide
$05 ΓÇö Check Instruction
$06 ΓÇö cpTrapCC, Trap CC, Trap V
$07 ΓÇö Privilege violation
$08 ΓÇö Trace
$09 ΓÇö Line A
$0A ΓÇö Line F
$0B ΓÇö unassigned
$0C ΓÇö CP protocol violation
$0D ΓÇö Format exception
$0E ΓÇö Spurious interrupt
$0F ΓÇö Trap 0ΓÇô15 exception
$10 ΓÇö Interrupt Level 1
$11 ΓÇö Interrupt Level 2
$12 ΓÇö Interrupt Level 3
$13 ΓÇö Interrupt Level 4
$14 ΓÇö Interrupt Level 5
$15 ΓÇö Interrupt Level 6
$16 ΓÇö Interrupt Level 7
$17 ΓÇö FPCP bra or set on unordered condition
$18 ΓÇö FPCP inexact result
$19 ΓÇö FPCP divide by zero
$1A ΓÇö FPCP underflow
$1B ΓÇö FPCP operand error
$1C ΓÇö FPCP overflow
$1D ΓÇö FPCP signalling NAN
$1E ΓÇö PMMU configuration
$1F ΓÇö PMMU illegal operation
$20 ΓÇö PMMU access level violation
Macintosh Portable ROMs:
The bootup code in the Macintosh Portable contains a series of startup tests that are run to ensure that the fundamental operations of the machine are working properly. If any of those tests fail, a Sad Mac icon appears on the screen with a code below that describes what failure occurred. Here is a typical example of a Sad Mac display with an error code below it:
 
The two codes are actually the contents of the two CPU data registers D6 and D7. The upper word (upper 4 hex digits, in this case 0546) of D7 contains miscellaneous flags that are used by the start-up test routines and are unimportant to just about everybody except a few test engineers within Apple. The lower word of D7 is the major error code. The major error code identifies the general area the test routines were in when a failure occurred. D6 is the minor error and usually contains additional information about the failure, something like a failed bit mask.
 
The major error is further broken into the upper byte that contains the number of any 68000 exception that occurred ($00 meaning that no exception occurred), and the lower byte that usually contains the test that was being run at the time of failure. If an unexpected exception occurred during a particular test, then the exception number is logically ORed into the major error code. This way both the exception that occurred as well as the test that was running can be decoded from the major error code:
 
In this example, the code says that an address error exception ($0200) occurred during the RAM test for Bank A ($03); $0200 ORed with $03 = $0203.
Major error codes
Below is a brief description of the various test codes that might appear in the major error code:
ΓÇó Warning: Some of these codes may mean slightly different things in Macintosh models other than the Macintosh Portable. These descriptions describe specifically how they are used in the Macintosh Portable.
$01 - ROM test failed. Minor error code is $FFFF, means nothing.
$02 - RAM test failed. Minor error code indicates which RAM bits
failed.
$05 - RAM external addressing test failed. Minor error code
indicates a failed address line.
$06 - Unable to properly access the VIA 1 chip during VIA
initialization. Minor error code not applicable.
$08 - Data bus test at location eight bytes off of top of memory
failed. Minor error code indicates the bad bits as a
16ΓÇôbit mask for bits 15ΓÇô00. This may indicate either a bad
RAM chip or data bus failure.
$0B - Unable to properly access the SCSI chip. Minor error code
not applicable.
$0C - Unable to properly access the IWM (or SWIM) chip. Minor
error code not applicable.
$0D - Not applicable to Macintosh Portable. Unable to properly
access the SCC chip. Minor error code not applicable.
$0E - Data bus test at location $0 failed. Minor error code
indicates the bad bits as a 16ΓÇôbit mask for bits 15ΓÇô00.
This may indicate either a bad RAM chip or data bus
failure.
$10 - Video RAM test failed. Minor error code indicates which RAM
bits failed.
$11 - Video RAM addressing test failed. Minor error code contains
the following:
upper word = failed address (16-bit)
msb of lower word = data written
lsb of lower word = data read
Data value written also indicates which address line is
being actively tested.
$12 - Deleted
$13 - Deleted
$14 - Power Manager processor was unable to turn on all the power
to the board. This may have been due to a communication
problem with the Power Manager. If so, the minor error code
contains a Power Manager error code, explained in the next
section.
$15 - Power Manager failed its self-test. Minor error code
contains the following:
msw = error status of transmission to power manager.
lsw = Power Manager self-test results (0 means it
passed, non-zero means it failed)
$16 - A failure occurred while trying to size and configure the
RAM. Minor error code not applicable.
Minor error codesΓÇöPower Manager processor failures
If a communication problem occurs during communication with the Power Manager, the following error codes will appear somewhere in the minor error code (usually in the lower half of the code, but not always):
$CD38 Power Manager was never ready to start handshake.
$CD37 Timed out waiting for reply to initial handshake.
$CD36 During a send, Power Manager did not start a handshake.
$CD35 During a send, Power Manager did not finish a handshake.
$CD34 During a receive, Power Manager did not start a handshake.
$CD33 During a receive, Power Manager did not finish a handshake.
Diagnostic Code Summary
Below is a summarized version of the Sad Mac error codes:
Test Codes
$01 ROM checksum test.
$02 RAM test.
$05 RAM addressing test.
$06 VIA 1 chip access.
$08 Data bus test at top of memory.
$0B SCSI chip access.
$0C IWM (or SWIM) chip access.
$0D Not applicable to Macintosh Portable. SCC chip access.
$0E Data bus test at location $0.
$10 Video RAM test.
$11 Video RAM addressing test.
$14 Power Manager board power on.
$15 Power Manager self-test.
$16 RAM sizing.
Power Manager communication error codes
$CD38 Initial handshake.
$CD37 No reply to initial handshake.
$CD36 During send, no start of a handshake.
$CD35 During a send, no finish of a handshake.
$CD34 During a receive, no start of a handshake.
$CD33 During a receive, no finish of a handshake.
CPU exception codes (as used by the startup tests)
