It sounds like we probably do need that prom dumped then.
Do you have any means to cleanly desolder it so it can be soldered back with no board damage?
Do you have a hakko fr300 (or its predecessor the 808) desoldering tool, and some 60/40 solder (and a temp controlled soldering iron) to wet/re-wet the pins with while de-soldering? Some paste flux may or may not help as well.
EDIT: Also what is it with DEC always assuming every prom is open collector and having a 5v pullup resistor array outside of them? I noticed this while trolling schematics for the past week. (They seem to have mostly stopped the pullups around 1983, dectalk era). Was this just DEC being anal about availability of replacement parts so they could use either an Open Collector or a Tristate PROM when replacing one during field service?
Last edited by Lord Nightmare; 05/03/15 04:23 PM. Reason: add question/rant about dec and pullup resistors on proms