Kathy's "trusty dusty"  PT-80 Casio keyboard is back and as good as new, thanks to a thorough cleaning from an electronics repair shop. She said it was hard to find someone who would do it, but apparently the technician who agreed to do it got rid of lots of "crud" inside that was making the keys stick, among other problems.
So now we have three keyboards, including both this Casio SA-39 and this Casio SA-76 that I found last summer and somehow thought were the same size as the PT-80. Kathy had been using the SA-76 which has many nice features and a great sound. But it's far heavier than the PT-80, so much so it made Kathy's music stand slowly shorten during rehearsal or Mass.
Nowadays, smartphone keyboard and pitch pipe apps are making these keyboards unnecessary, but Kathy neither has nor wants a smartphone.
 Or, as several eBay sellers describe the PT-80, "vintage."