On 08/01/2017 18:20, "Tony Duell" <[email protected]> wrote:
>> However, two of us bought units at the same time and the other one has a >> little bridgeboard containing a 74LS244 that sends the RGB signals to a DIN >> socket on the back of the case for an external monitor. I also can't see a > > And in a sense there was... Yep. I'm pleased we found that mod in the other unit because I made my own bridgeboard and hooked the display up to a Microvitec CUB, I got exactly the same picture (in colour) on that as I did in mono on the 5" TV so I knew the analogue board and TV were OK. >> luminance line on the connection to the TV board on mine, just >> red-green-blue with sync and inverse sync which go to the horizontal driver > > Do you mean that the common cathode connection of those diodes goes to > the monitor connector but nowhere then on the monitor PCB? No, in trying to trace some of the lines along the bottom of the board I took the monitor cable off and traced the pins. They are: 1 - 5V 2 - NC 3 - looped to 5 4 - Sync out 5 - looped to 3 6 - emitter of V326 via R336 7 - GREEN 8 - RED 9 - Inverse sync (which also goes via R332 to the base of V333) 10 - BLUE 11 - GND 12 - GND 13 - 12V 14 - 12V >>> Is the MR9735 doing anything? Is it accessing memory, for example? >>> I still wonder if it has to be initialised (say to vewdata rather than >>> teletext mode) and if this is not occuring. >> >> Its address and data buses are active as is the pair of 2114s that are >> acting as a page store. There's a 74LS240 buffering the data bus and that's >> active. > > OK.. My dislike of 2114s is legendary, but probably not the problem here.... They're OK too, surprisingly. I took them off the board and put them in a PET8032 as video RAM. >> You could be right though, I'm not convinced the unit is actually running >> any code yet despite the ROMCS lines working and I can see activity in all >> 16 RAM chips. Data bus and address bus at CPU and ROM chips looks happy from > > What are the RAMs? If they're more 2114s I wonder if they have problems > that are confusing the CPU (perhaps corrupting the stack?) 4116-2 wired as 2 banks of 8. >> a 'doing something' point of view. All the control lines on the CPU are >> pulsing with the exception of IO/M but if all the IO the chip is doing is to >> memory then that's to be expected. > > What's the CPU? 8085? I've had those fail in odd ways. Yeah, 8085A. Thanks to list members I have some spares to try. >> I've disassembled the ROM code so I'll have a look through that for an init >> routine, also the datasheet should tell me what its expecting at powerup. > > Personally, I'd stick a logic analyser on it and start tracing the code. See > if it is executing anything correctly. I've only got a cheap-ish Saleae compatible 16 channel analyser. Watching code is a bit above my current level of self-paced learning :) -- Adrian/Witchy Binary Dinosaurs creator/curator Www.binarydinosaurs.co.uk - the UK's biggest private home computer collection?
