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The keycode assembly on my HP 8663A is failing to interrupt the microprocessor. To narrow down the fault to an IC, I was hoping to use signature analysis on the keycode assembly. In the manual I have (2234A to 2927A, vol 2) under service sheet BD9 there is a "KEYCODE STIMULUS DIAGNOSTIC", which states the following:

This test stimulates the A2A1 Keycode Assembly for signature
analysis testing. Refer to Service Sheets 61 and 62 troubleshooting
information for procedures and the use of this Diagnostic.

However, when I refer to the these service sheets in vol 4 (same serial prefix range) I don't see any signature analysis information. Each service sheet contains a block diagram, a component locator and a schematic, but I don't see SA information on any of these. I was expecting to see 4-digit hex sequences by various nodes in the schematics. Or, I was expecting to see something like the signature analysis table in the "SIGNATURE ANALYSIS I/O DIAGNOSTIC". What am I missing?

Hi Matt

My service manual P/N is 08663-90071, covering from 2234A to 2927A and found nothing about that keystrokes :(
However, my unit has serial 2846A opt 002, if you need data or whatever for comparison, tell me. Maybe I can help ;)

Regards,
R.

I'm not familiar with the 8663A, but I did have a problem once on my 8780A where the keypad didn't respond.? The problem turned out to be a broken copper leaf spring underneath the "8" key.? The key contact was being shorted closed and to the instrument, it appeared that the "8" key was always being depressed.? To the user, the entire instrument keyboard appeared as non-responsive.

After I figured out the problem, I realized why a single "8" always appeared on the display after the instrument powered up.? Doooohhh! :-)?