Compucolor 8001 Sonalert siren

[johnx993]

My 8001 starts with a constant siren from the Sonalert disc affixed to the bottom chassis.
Not sure if this is some sort of power-on test reporting an error; or it was never designed to do that, and something is broken and just happens to trigger it.
The only ref I can find to audio in the manuals is the ubiquitous BEL Ctl-G.
And it's loud!

 

[cruff]

Are the power supply voltages in range? Does the system otherwise work?

 

[johnx993]

Voltages look good, within 0.1V or so. And I'm getting phi0 and phi1 clock signals, though there is a bit of bounce.
I found the 'Sonalert' disc in the schematics. It's connected to +5V on the Analog Board and to line 13 of the keyboard cable.
This line goes to pin 30 of B4 on the CPU card. This is a TMS 5501 I/O chip and pin 30 is output bit 6 (inverted).
So, O6 would have to be high, then represented as low at pin 30, then go to the Sonalert, which takes +5V on it's other connection.
Sadly though, not all chips are socketed. I'll just have to pick my way through the bramble...