Small progress to report.
I've swapped out quite a few 4016's and 4013's, with no success.....except for one. When another new 4069 was installed, the trombone came back to life. But only the trombone, not the trumpet.
I've been trying to find equivalents for these chips. (I don't mind ordering new chips, but I have quite a few spare 7400 series ic's in my parts supply, so if there are some equivalents to the 4000 series, I'd like to use them up. Sometimes I get lucky! )
909 (op amp)
TDA1022 (bucket brigade delay)
4011 (2 input quad NAND gate)
4082 (4 input AND gate)
4071 (OR gate)
Here's a few more details on the Quartet's misbehaviours.
There's a fairly fast "ticking" sound that is always present. Around 200 bpm, I'd estimate.
The strings and trumpet are heard, but barely. Like, I didn't even know they were playing until the room was silent.
Nothing at all from Honky Tonk piano or Celeste.
Organ, Trombone, and Piano are fine. Probably not the best idea for a band though.