Hi TurboPC
Thanks for your reply and suggestions, which are very helpful indeed. Like yourself, I worked with ATEs for many years too, and some of the methods you pointed out I've tried before.
The ATE I am having problem with at present is a Schlumberger S750. It is quite a piece of machine, though a little aged (over 10 years in use). Why I suspected the tester is because the PCB I am working on passed all the small ICs consistently and easily 2 months ago, but after the spares came and I replaced the defective IC, some small ICs started failing. My colleage has two such PCBs on hand and I borrowed them to help isolate the cause. They too failed the same ICs as on my PCB. The ICT fixture is in pretty good condition due to low usage, so naturally my suspicion rests on the tester.
In fact, about 2 years ago, the power supply (5V 120A) that drives the tester's test electronics died and we spent over two weeks recovering it. Since then, we have occasional hiccups when the tester seems to behave strangely. I have called on my maintenance support contractor who performed self-test on the tester but each time no problem was reported. As I see it, the self-test fixture uses a straight through loop-back wiring to test the driver/receiver circuitries, and therefore if there is a degradation on those drivers which cannot provide sufficient backdriving on heavily loaded nodes, the in-circuit routines will most likely fail.
I have given quite some thoughts as to how to do a realistic self-test that will isolate those 'weak' drivers, but as it is company's asset, I need to know the correct technique so as not to damage the tester.
Most PCBs that I work on are military related, so it is not convenient to release (sorry about that). But I will be glad to share insights with you on anything that will be helpful to you in return (but I assume you have more years of experience than me as regard to testing).
Still, glad to know you bother to take the time to help. Thanks!