HP 9845 C with 280 option startup failure

IT's not as bad as it looks. The 2 ROMs form a 16 word * 13 bit table (3 outputs of U34, 1816-1397 are not wired, the A4 input of both ROMs is tied to logic 0). The ROMs are addressed by a '163 counter. It can be parallel loaded from 4 of the ROM outputs, the load is controlled by that '150, the select inputs of that are the same signals as the ROM address lines. OK, here's a pinout from the schematic. Rear of machine, looking down into the edge connector on the 98770-66534 board MonAck/ --( )-- WrFull/ MonStb --( )-- DD15 Gnd --( )-- MonClrAddr/ Gnd --( )-- +5V MD(6) --( )-- +5V MD(7) --( )-- +5V MD(4) --( ) N/C MD(5) --( )-- -Vm MD(2) --( )-- -Vm MD(3) --( )-- +Vm MD(0) --( )-- +Vm MD(1) --( )-- Gnd MD(9) --( )-- Gnd MD(8) --( )-- MD(12) MD(11) --( )-- MD(13) MD(10) --( )-- MD(14) DA14 --( )-- Gnd Gnd --( )-- Init/ Where : +Vm = +18V monitor supply from mainframe PSU -Vm = -18V monitor supply from mainframe PSU DA14, DD15 are 2 blanking/control signals (derrived, sortof, from address 14 and data 15), mainframe to monitor Init/ = mainframe reset signal (to monitor) MocAck/ = Vertical timing signal from monitor text PCB MonStb = Charater strobe from monitor text PCB WrFull/ = Buffer full (to monitor text PCB) MonClrAddr/= Clear buffer memory address (end of line) from monitor text PCB MD(n) = 15 bit date word to monitor text PCB 0...6 == Ascii code 7 = chracter set seelct (or alternatively, 0..7 = character code :-)) 8 = cursor at this location 9 = inverse video 10 = blink 11 = underline 12..14 = colour select (not used on mono monitor) You really need the schematics :-) For reference the other monitor connector, on the 09845-69555 Printer Driver PCB is just the PPU I/O bus : Rear of machine, looking down into connector PA(2) --( )-- +5V PA(3) --( )-- +5V PA(0) --( )-- +12V STS/ --( )-- -12V PA(1) --( )-- Flg/ DMAR/ --( )-- Dout/ IOSB/ --( )-- Gnd IRH/ --( )-- Gnd IC(1) --( )-- IOD(1) Int/ --( )-- IOD(0) IC(2) --( )-- IOD(3) IOD(14) --( )-- IOD(2) IOD(15) --( )-- IOD(5) IOD(12) --( )-- IOD(4) IOD(13) --( )-- IOD(7) IOD(10) --( )-- IOD(6) IOD(11) --( )-- IOD(8) Gnd --( )-- IOD(9) Where the signals are just unbuffered versions of the signals on the I/O slots (same as a 9825, for example). Is the above of any help? -tony