Why do the same parts sometimes pass and sometimes fail?
First confirm that both the power ON and front panel self test PASS?
When doing the self-test it is essential that all fixtures (including the AC interface) are removed and that all RS232 connections are removed. The safety interlock needs to be left connected.
If all self tests PASS perform the following steps:
Ensuring that you have a successful compensation, tests will not be successful if compensation is incomplete or fails.
If a test program still fails, inspect the top spring test probes to ensure that there is adequate spring tension. These probes make contact with probes mounted on the fixture plate and any contamination between these two probes may cause an intermittent contact or possibly no contact at all. An intermittent contact at the fixture may explain why inconsistent compensation and test results are seen.