Great work on the PC-X ... and good to see Axel "on board".
A few finds ... I had wrongly assumed that the PC-X used the OMTI 5300 MFM hard disk controller (which has a connector for a tape streamer as opposed to the OMTI 5100) ... Axel's PC-X uses a DTC520B. Now I suddenly wasn't sure if I had imagined mention of the 5300, but it's there ... in the Servicehandbuch Teil 1, page 217 relative to the PDF.
https://dl.dropboxusercontent.com/u/55419307/Siemens%20PC-D%20Servicehandbuecher.zipI'm still baffled by the beep after the "Test End" message, which should be quite short.
Servicehandbuch Teil 1, page 194 says that the loudspeaker is driven directly by Timer 1 of the 80816 (if I read the source right, that's implemented), and that "to help switching on and off of the speaker, one bit of the Device Control Register is used ... Bit D5 = 0 switches the speaker off, Bit D5 = 1 switches it on"
There's also a sort of beeper on the keyboard that can produce key clicks and beeps (duh!) ... cf. page 174.
