There is a lot of circuitry connected to the piezo. I'll trace it out.

OK, it's an oscillator that R15 enables. It's got the same wiring as this:

C1 and C2 are 0.003uF, R1 and R4 are 1K, R2 and R3 are 100K.

Instead of a battery, the common resistor leads are connected to the TMS's R15 output and one side of the piezo. The other side of the piezo is connected to T1's collector.

I connected a resistor between pin 5 of the TMS socket on the PCB and VSS, and measured a 2.4kHz signal at the piezo.

And that works out well with the equation on that web site, which gives 2.405kHz.

Entex Jackpot Blackjack/Gin Rummy has the same circuit, but the components are laid out a lot easier to trace! Pretty much exactly like that schematic was drawn.

Last edited by seanriddle; 04/23/15 10:37 PM.