Narrowed list of causes for chip tester failure, instrumented M1000 card reader and looking at problems

 CHIP TESTER ISSUES WITH SN74182N CHIPS

As I outlined in the previous post, I first checked the chip on a breadboard to assure myself that the entire group of chips weren't bad with the same fault. As I expected, when all four P (propagate) inputs were low, the P output was indeed low even though the tester reports it as high. 

Further the voltage was low enough that I discounted any issue with invalid levels causing the tester to see the result as high. I hooked up the scope and watched the tester first set the P inputs high with the P output validly high, then drop the P inputs which forced the P output low. The tester, however, claimed it was high and flagged it as an error. 

I have contacted the designer as he may not have tested this particular chip type and there may be a defect in the test itself. I may put the logic analyzer on the signals to see whether this is a race condition in the test or a real issue.

INSTRUMENTED CARD READER FOR INTENSIVE DEBUGGING

I wired up 32 of the 34 signals from the backplane to the logic analyzer where I can record their state as it operates. The two I didn't record are Power-On-Reset and Reset, neither of which are germane to debugging the operation of the reader. 

FRUSTRATING STATE OF CARD READER

With the logic analyzer hooked up, I can see odd status of some of the signals. I put the reader into its manual trigger mode so it will read cards as fast as it can, while watching the logic analyzer to see the outcome. However, the reader read the batch once and began acting up. It now indicates both Stacker Error and Read Check immediately upon the attempt to pick, before the card actually begins moving at all. 

I did check the power supply as flaky or substandard voltage levels could induce strange errors. It appears to be solid with almost no ripple. I am back looking for bad chips or other explanations for the misbehavior.