HP 8508A Operating & Service Manual page 128

Service
Error Code 500 indicates a ROM test failure. In this case a further ROM test is available as follows.
1. Power the HP 8508A off. .
2. Select Position 1 of the test switch on the Processor ansiabiy.
3. Power the HP 8508A on. Both the red and green LED's should come on and then both should rapidly
extinguish. If after approximately 6 seconds, the green LED should come on again and stay on, the ROM test
has been successful. If, however, the red LED should come on, the test has failed and the ROM (A5U18)
should be replaced. _
4. Switch the instrument off and replace the ROM.
5. Repeat the ROM test as in steps 2 and 3.
6. If the test should still not be successful, replace the AS Assembly.
Should another Error Code in the 500 series appear, the Processor assembly should be replaced with a new one. In
this case the ROM has passed its self test and can be re-used.
Note that a replacement Processor Assembly can be ordered either with or without a ROM installed. The part
numbers for both assemblies are given in Section 6 of this manual.
Reset the test switch to the "0" position and cycle the power to reset the processor to its normal operating mode.
Disassembly and Reassembly Procedures
Removing the Processor Assembly
To remove the Processor Assembly from the Vector Voltmeter:
a. Wear a wrist strap for ESD protection.
b. Remove the shatriiaaas Bottom Cover.
c. Disconnect the cable connections to the assembly.
d. Remove the 2 screws storing the HP-IB connector to the rear panel.
e. Remove the 6 screws securing the Processor Assembly to the Instrument deck.
f. The Processor Assembly may now be removed from the instrument.
Refitting the Processor Assembly
Refitting is the reverse of this procedure.
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