I like these old school monitors, yep that monitor has an Analogue/TTL toggle switch. Up to 64 colours EGA.

The 9 pin connectors are wired differently to VGA pinouts on some CGA/EGA CRTs.. apart from NEC and some Japanese domestic market ones.

I am guessing it is the former which means you probably need to adapt the pinouts like this:

Where as the latter is like this:

Regarding the 9 pin cable shown, I would open up it's connectors and see if either side has the Red, Green, Blue coax cables wired in a pinout that matches the NEC arrangement listed above.

If one side does match the NEC pin-out then just get a straight through Female DB9 to Male HD15 adapter and you are golden. Like : https://www.ebay.co.uk/itm/VGA-Adapter-DB9-Fe … er/293066192710

If not.. then I would make your own cable or find a cable for sale that definitely has that first pinout conversion.

Experimenting with analogue signals should be okay, It would be more harmful if you tried to put a TTL RGBI 5v signal when the monitor is expecting Analogue 0.7v on the RGB inputs but even then the input circuit would probably would survive.

Thanks Hanamichi.
I've checked the cable pinout and its just straight through, so have built myself an adaptor as per your first link.
Went to test it and have discovered bigger issues, the monitor is dead!
Power LED comes on, tube heater starts glowing, but I'm pretty certain I'm not getting HV as I'm not feeling any static on the screen that I seem to recall from CRTs. That saud, its been a long time since I last used one!
I'll dig in a bit more in the next few days, I want to do a little more research first to educate myself on the exact safety procedures, I know CRTs can be pretty nasty.
Thanks
Andrew

Shame it did not do the trick.

Hmm what you describe is kind of normal for my early CRTs, they have no OSD to show when there is no signal.

My pre 90s CRTs do exactly this, the tube does not glow at all until they get a H/V sync they are expecting, and then kick into life.
*Edit if the CRT has a TV tuner it does glow without signal. My (non digital scan, no tv tuner) CRTs do not seem to, you can hear a relay click on some when they detect the sync signal.

I know you mentioned you opened the back up, can you see the wire colours to the 9 pin input? Perhaps it is different to what I posted.

I can recommend these videos for more CRT knowledge:

Retrotech
https://www.youtube.com/channel/UCwOTvOtoAjiqQx1PCrfmTKw

For discharging:

Retro Recipes:
https://www.youtube.com/watch?v=a6FMpvs71pc

https://www.youtube.com/watch?v=x1DeMOl_nK4

Also the communities:
https://shmups.system11.org/viewforum.php?f=6 … c39d7907c6a386f
https://www.reddit.com/r/crtgaming/

I personally pull the power cord when the monitor is powered on as extra precaution to discharge as much possible before opening up a CRT monitor. (Instead of switching off on the monitor chassis.)
I would binge on CRT knowledge first and be careful, especially around the power supply caps and anode/flyback. I ended up buying Polyco electricians gloves for peace of mind.