Just a note to say I have found the fault with the 4011 replacement: I tested all 14 pins on the IC socket after removing the chip and.. one of the pins does not beep on the meter.. how can an IC socket not have continuity from top to bottom?
Anyway, it doesn’t, so I need another socket.
Maplins in Middlesbrough is still trading, so I’ll give them a try..
Update: not any more. I did buy a new socket before they closed, though.
Still got issues with it. I think some solder traces are damaged. I have bought some new lead-based solder to try and fix this.
The dr-55 schematic suggests that pins 10,12,13 should be connected together, so a continuity test should confirm that.
Meantime, I “found” another (broken) dr-55 in storage.. More of the same..