This turned out to be remarkably easy!
Step 1: de-solder the existing memory chip. This turned out to be an NEC equivalent of the Toshiba TC5501P.
So, 22 pins to desolder using my Duratool soldering iron and tools. The desoldering pump did the job yet again, with some cleaning up of the holes. My IC extractor came in handy again too.
Step 2: install the new IC socket. This is simple but tedious, making sure you don’t accidentally short any pins. All 22 of them.
Step 3: install the TC5501P chip into the socket. This was the most frustrating bit, mainly because the legs on mine were bent. (Someone stood on the envelope when in transit) I had to straighten each leg before insertion. Nasty.

I DID find the fault, though, and this was weird: two corroded legs on the old chip, one of which snapped off on removal. See photos..

Anyway, that’s all folks! It all works.. I spent an hour programming some of the sample rhythms in. And then some of my own- I’ve had these things forever.. so simple to program.

I’m tempted to sell, since they are worth at least £200.. but I might not find another.. dilemma..

{RANT} – Note to Americans: It’s “solder” as in “soldier”, NOT “sodder”. I am sick to the back teeth of Americans saying “Sodder” on Youtube videos. {/RANT}