I am trying to get this analogue tape langauge lab system ASC model 4M up and running. I believe it dates from the late 80s. It consists of a master control panel and several 2-track slave decks. These are interfaced using a bus and ASCII command strings (that's as far as my knowledge goes on the IT side of things!).
schematic part 1:
print side of the pcb:
There are some pictures of the equipment here:
The problem was caused on assembling the master panel's processor board: I accidentally connected the cable 105 which was supposed to go into connector 105 (from student control unit which supplies the slave decks) into socket 103 (they are the only two in the whole system which are the same size!). You can see on the schematic that pin 25 of 105 carries a +7.5v supply and 13-14-26 appear to have +5v on them. So these voltages were fed into the corresponding pins of number 103, and ended up God-knows- where, the 7.5v went on the AO line.
On powerup, a few lights came on on the console, but it was several seconds before I realised something was wrong and yanked the plug. Since then, the main console appears dead, with a very faint display on the LCD and nothing else. the individual slaves work, but receive nothing from the master console. The 'good' news is that since 105, which supplies a 5v and 7.5v supply, was not in its place, there were no other voltages around on that panel whilst the misconnection happened.
Could this be some eeprom got scrambled or one of the IC's blew? What I need to know now is what components are likely to have been affected by this misconnection, and what to start replacing. I tried replacing IC115 (8155) by subsitution from a student machine, no change. removing the ICs one by one (except IC108 to IC111) usually made no difference, but IC107 74HC138 caused the LCD to come on with garbage on, and a few random lights to come on. However, exchanging it for one of the others made the unit dead again.
ICs include.
74HC138AP SS74HC241E PC74HC00P D8259AG2 TMP8251AP D8505AHC-2 M74HC623B1 74HC573AP ULN2803A RAM: 6116 2764 27128I know this is a long shot, any ideas on what to start replacing? I've no idea how easy to come by most those chips are. Thanks for any ideas B