HP 9845 C with 280 option startup failure

What, all different colours, to indicate the colour that the text (or whatever) will appear on the monitor? The HH Tiger did that. When you say 'half as somplex', do you mean it only has one main chopper circuit, not the 2 that are used in the 9845B Opt 200? I have never seen a 9845A, but from what I've heard it's very different to the B or C. To the extent that both processor modules are on one PCB, and there's a bus switching board alongside it. Yes. And it's not just one supply line either. There's certainly +5V, +12V and -12V for the logic, and I think +18V and -18V (Vm on my diagrams) for the analogue side. The mono monitor is also quite complex inside. There are 6 plug-in PCBs + a backplane and a little function keystrip under the screen. The flyback transformer, which supplies the high voltages for the CRT, is seperately mounted on the chasis metalwork. The 6 PCBs split into 2 sets of 3. The first is the digital stuff and consists of : Text PCB : ---------- Takes in characters from the 80 cahracter buffers on the mainframe video interface PCB. Contains character generators, video shift register, attribute logic, video timing/sync chain, etc. Interface PCB : ---------------- Linkls to the PPU I/O bus. I/O address decoder, control/status register, keypad encoder, etc. Processor PCB : --------------- Graphics memory, HP ASIC as an address generator (both for read/display and things like line drawing), graphics shift registers, rubberband memory, etc. There must be around 200 ICs on those 3 boards in total The other 3 boards are the analogue stuff you'd expect (!) to find in a monitor. Deflection PCB : ---------------- Scan oscillators, vertical output stage, SMPSU for the flyback transformer (!), raster correction circuit Video PCB : ----------- Video DAC (resistor ladder, actually), video amplifier, CRT driver circuitry Heatsink PCB : -------------- 6 power transistors. Raster correction output, horizontal supply regulator pass transistors, horixzontal output transistor, flyback driver transistor. Note that the yoke has 3 windings. As well as the conventional deflection windings, there's a feedback sense winding that measures the actually horizontal deflection field. There are 2 expansion slots in the monitor. One is for the lightpen controller. THe other is for an arbitrary video expansion board. I have neither option, so there are no schematics. First problem (for you, at least). I drew all this out long before seeing an HP manual, so I didn't use the HP names. And several of the signals disappear into the PPU hybrid so it's almost impossible to work out what they actually do there. I have now seen the HP boardwapper guide for the monitor, but I couldn't easily work out the translation between my names and HP's. -tony