[TUHS] Codata restoration - day 1

Hi, after carefully examining the power supply and checking the generated voltages, we were convinced that this wouldn't kill our Multibus boards. Maybe some of you are interested in our progress, so I though I would send you an update. After reconnecting the Multibus backplane, we started the system with only a CPU board and a memory board. On one of our CPU boards the smaller (P2) Multibus connector is masked with tape, I'll have to dig deeper to find out what is deactivated by this… One of our two CPU boards is currently non functional (the one without the masking take, this doesn't say a thing on the console UART, will bring in the scope in Monday to check for details). The other one brings up the monitor startup message and prompt on a connected serial terminal (emulator) - however, we are unable to get any characters echoed back. The serial cable is working, we tried all sorts of handshake configurations. If we get any characters back (the system is running at 9600 baud, I tried all combinations of 7/8 bit, none/even/odd/mark/space parity and 1/2 stop bits), these are garbled and contain mostly "1" bits (0xfc, 0xfe, 0xff or similar). The UART itself seems to work (exchanged it with the one from the non working board - same result), so now I suspect the AM26LS32 RS423 driver to be the culprit. I uploaded some pictures to http://s1372.photobucket.com/user/michaelengel/library/Codata?sort=3&pa… - there you can see that this machine is far from being in any sort of original condition. Nevertheless, it's great to see it come alive again! Btw., current versions of MAME/MESS include a rudimentary Codata simulator. This doesn't do very much so far, but it can successfully run the firmware ROM code (picture also uploaded to photobucket). Best wishes, Michael