Resolved: VAX-11/750 ECKAL (Cache/TB) Diagnostic failure

Hey all -- I resolved the weird failure I was seeing on my 11/750 with the Cache/TB diagnostic and since it was fairly random I thought I'd share it to save people from the future (hi, people from the future!) from going through the same machinations I did. Issue: ECKAL diagnostic loads, prints banner and halts after about a second with: 00003488 06 No other diagnostic is provided, and since there don't appear to be any listings or real documents covering the test, it's not particularly helpful. What I tried (prior to tonight): - Checked voltages. - Double-checked backplane for bent/shorted pins. - Cleaned and reseated every socketed chip (especially the gate arrays). On *all* boards. - Swapped in a spare L0003 (after cleaning, as above). - Swapped in all the other spares I have (one at a time, again, after cleaning). - Cleaned backplane with contact cleaner. - Removed 2nd UNIBUS card. - Tried a *third* L0003 card (labeled "GOOD" as of 1996 :)). No change in behavior whatsoever. Very odd. Very frustrating. So tonight I thought, hey, why not disconnect the UNIBUS just in case something odd is going on there. Pulled the Unibus jumper connecting the two backplanes, replaced with terminator. ECKAL diagnostic now runs and passes. So: This particular fault (at least in this case) is due to some oddity on the UNIBUS. I suspect a problem with NPG grants, but I'm going to have to go over this with a fine-toothed comb, it could be a bad controller in there doing something mean. Hope this helps someone at some future date... - Josh