Old analogue monitor help?

Hi Julian,

Sorry I can't help you with this as I lack experience in this area but I wanted to complement you on the nice preparation and explanation. Most questions come with not enough pictures or preliminary research. I hope one of the engineers on the site will have some insights for you.

John

Could you upload photo of back case of this monitor ? There should be information about model and chassis.

It looks as if the design has extended the socket from the processor board to the back of the box so that new eprom chips (probably with updated code or data) can be plugged in - a primitive form of the plug in games on early home gaming machines.

The ESP8266 is not a good chip for a beginner to try and make a video driver you would do much better with an ARM based general purpose micro on a cheap dev board for example an ST Nucleo-F411RE You can use free tools and the processors has a good set of timers and peripherals that will help with the task

Next you will need to check what sort of video interface is used between the micro controller board and the CRT board (composite or separate)

Here's a book about that kind of steam powered video - if you can plough through the whole thing you'll know loads of good stuff and enough to try doing most of it in code on a uP.

https://www.tinaja.com/ebooks/tvtcb.pdf

Google for other stuff about MC6845 etc to learn more.

Take a picture of the connection between the crt board and the micro board and post it here in case someone can spot anything weird to warn you about.

For a real learning experience try re-coding the processor you already have on the board !

MK

I agree with MK. If it were me, I'd do something with the original processor since it's all there and presumably working. I doubt you'd have too much of a problem finding a cross-assembler that you could use. You'd need a way to erase the EPROM (UV light in an eraser box) and reprogram it (programmer) (read the contents and save it to a file before you erase it the first time). (Note, it's not an EEPROM, but if you could find an EEPROM with the same pin-out and similar specs it might be easier to work with than the EPROM - you'd just need the programmer then).

Otherwise you could either replace it entirely and have the design job of getting a microcontroller to generate video waveforms (not as easy as you might think, unless you just copy something that someone else has got working, if there is such a thing) or you could try and find a way to interface a microcontroller to the 6847 (quite messy, but might be possible). Some of this depends on what you want from it. If you just want a terminal to use, I'd say work with the original or substitute something that's already been done. If you want a microcontroller project to learn with, weigh up the various approaches and decide which interests you, what you feel you might be capable of, and whether you have suitable equipment to do it (oscilloscope, for instance) .

Display interface is a 6847. Bit later than the 6845 - has more integrated on the chip - internal character ROM and puts out Y (luminance)  and colour-difference signals.

Possible that the output might be composite - the two transistors on the left look like they might be a circuit for combining the HS and VS with the Y output. Find pin 12 (Y output - that's the luminance signal) of the 6847 and trace where it goes (you might need to carefully lift the chip out of its socket to see tracks underneath). Also trace the HS and VS outputs. Draw the circuit as you go and you'll then have a diagram of the video output stuff and know how it drives the monitor.

Are you familiar with the expression, the emperor is wearing no cloths! Based on your skills resume “I've very little understanding of analogue electronics, a vague understanding of digital electronics and mediocre programming skills.” the project has a skill set requirement you fall short off. I’m not confident you can find sufficient support to complete such and undertaking.
 

Reality check. I didn’t see any mention of schematics, you may want to see what you can locate. The company you purchased it from may have some dog eared, brown paper copies they will let you have. They may also refuse to help you based on releasing gaming technology knowledge restrictions. Do you know if the unit worked before it was sold? Hopefully it did.
 

I am guilty of taking on enthusiasm projects, to later, much later, suffer the loss of defeat not completing them. Some of your commentary leads me to believe you may have undersold your skills inventory. I don't wish to discourage you put rather have you take a second look before leaping. Initiative, fortitude and perseverance you may have in abundance to carry you to the finish line.

Sean

I definitely understand what you mean, however this only encourages me more. Luckily, I'm doing something somewhat relevant at university, and so I've access to some very friendly professors and a very decent electronics lab (after summer, obviously). I also thought turning to this site (as advertised by Ben Heck, literally in the intro) would help me to get the knowledge I need.

There's actually nothing regarding model numbers or series of some sort. I think the company OTT Keyboards actually made the outer chassis of the monitor themselves, or it was a generic monitor which any company could simply rivet their little badge on the back of and sell it as their own. The inside boards lack information too. I will look for more information regarding the main PCB of the CRT itself. Maybe I can find some sort of label there. Here's a picture of the back regardless;

Ah yes, the old days.

Usually there was a vertical and horizontal sync line plus video, which would cover your six wires.

We used to put the digital data into a memory chip and then use counters to pull each bit out to drive a transistor or analog IC to drive the zero to 1 volt video.

We also used a PROM to take eight bits of memory and translate it into the video signal. The output was limited to 256 character types for building the graphical display.

Yes, the keyboard was usually a serial connection.

The ROM chip probably included Basic, so the simple OS would boot up and then allow you to type in the code.

Storage might have been to a cassette player to load and save your software.

If it was a video game, then everything would run from the ROM.

Brings back a lot of memories.

The circuit is not too complicated and we did this type of implementation when microcontrollers first came out.

DAB

You sound like the exact person I need for this. Do you know of any current hardware I could easily code for, that could use those 6 cables? I'm happy to provide as much information as I can find on this little monitor, and I'd absolutely love some help.

Let me did into my archives to see what I can find.

In the meantime see if you can piece together a block diagram of the system.

DAB