This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
IIgs Diagnostic Self-Test Error Codes By: a list by Jeff Tarr, Jr., Apple IIgs Technical Reference by M. Fischer, and IIgs TechNote #095 by Dan Strnad The IIgs self-test is activated by pressing Open-Apple and Option on power up, or Open-Apple, Option, and Reset. During the test, the test number (in hexadecimal) is visible on the bottom of the screen followed by six zeros. After all tests are complete, a continuous 6 KHz one-second beep sounds and the screen displays a System Good message. If a test fails, the screen immediately displays a message "System Bad: " followed by an eight-digit code (in hexadecimal) on the lower left hand side. The code is also displayed staggered in the upper left hand area to help you read it in the event of a display RAM failure. In case there is a video failure, the code is also sent to the printer port. Example 1: You get the message "System Bad: 05020000" This indicates failure of Test #05, the Fast Processor Interface Speed Test. The "02" says that the FPI got stuck in Fast mode (i.e. it could not switch to "Normal" Slow speed when asked to). Test #05 does not use the last four digits. Example 2: You get the message "System Bad: 080200D4" This indicates failure of Test #08, the Battery RAM Test. The "02" says that there was a problem reading and writing a test value to some address. Next, the "00" says that the test value was $00. "D4" says that the problem occurred with address $D4 in the Bat RAM. Diagnostic Self-Test Error Codes Error Codes are eight hexadecimal digits in the format 'AABBCCDD'. The first two digits (the "AA" part) always show the test number. The meaning of the remaining six digits depends upon the particular test. (There may be a few differences in the GS diagnostic self-test depending upon ROM version. For example, earlier GS's may not include Test #0C (AA= 0C).) ROM Test:G AA= 01 BB= Failed checksum DD= 01: RAM error Note: A ROM failure will also be denoted by "RM" in the top left hand corner of the screen. RAM 1 Test:H AA= 02 BB= __: Bank number CC= Bit(s) failed FF: ADB Tool error Soft Switches:M AA= 03 BB= State Register bit CC= Read addr. Low Byte Address Test:K AA= 04 BB= __: Bank number CCDD= Failed RAM Address FF: ADB Tool error Speed Test (FPI): AA= 05 BB= 01: Stuck slow 02: Stuck fast Note: If a ZipGS accelerator card is installed and not disabled and DIP Switch 1-4 (Counter Delay) is not set OFF (the normal, default setting), your GS will bomb on Test 05. John Link reports that a TransWarp GS with the v1.5 ROM will fail the Speed Test. In neither case does failure indicate any actual malfunction. Serial Test:1 AA= 06 BB= 01: Register R/W 04: Tx Buffer empty status 05: Tx Buffer empty failure 06: All Sent Status fail 07: Rx Char available 08: Bad data Clock Test:H AA= 07 DD= 01: Fatal error occurred - test aborted Bat RAM Test:F AA= 08 BB= 01: Addr. unique CC= bad addr 02: NV RAM pattern CC= bad patt DD= bad addr ADB Test:J AA= 09 BBCC= Bad checksum DD= 01: Fatal error Shadow Register: AA= 0A BB= 01: Text page 1 fail 02: Text page 2 fail 03: ADB Tool call error 04: Power on Clear bit error Interrupts Test (Mega II and Video Graphics Controller): AA= 0B BB= 01: VBL interrupt time-out 02: VBL IRQ status full 03: 1/4 sec interrupt 04: 1/4 sec interrupt 06: VGC IRQ 07: Scan line Note: There are reports that if a ZipGS accelerator card is installed and not disabled, then, your GS may fail parts of this test depending upon DIP Switch settings. Such a failure does not necessarily indicate a hardware fault. Sound Test:3 AA= 0C DD= 01: RAM data error 02: RAM address error 03: Data register failed 04: Control register failed 05: Oscillator interrupt timeout Note: There are reports that if a ZipGS accelerator card is installed and not disabled, then, your GS may fail parts of this test depending upon DIP Switch settings. Such a failure does not necessarily indicate a hardware fault. Other AA= FF (test number= $FF) According to M. Fischer this shows a likely problem with the Mega II chip because that test number is used only during manufacturing testing. By: Paul Creager