Had a problem that I had not seen before on a Stern Hot Hand. Within about half a second of powering the game up a continuous sound came from the speaker. The game would play normally, with all of the normal sounds, but the continuous sound was always present. After poking around with a logic probe a bit I tracked it down, a bad 7475 at U4. Just posting this here in case someone has a similar issue. A bad 7475 at U3 or U5 (if present) could cause a the same problem, I assume.