Just a quick update of no success yet. I have put the regulators back on, replaced the capacitor and zener diode but I have 1v output from the Fet in the
power stage. It's possible the Fet is stuffed, will replace that next and see what happens.

Do you have any idea which exact model this is? I have a Cypress scaler but it's not so good. Scaling quality is bad, black levels are incorrect and everything is stretched to 1920 pixels. Also, Hz in == Hz out with mine, so if you output 70 Hz and tend to use this on a LCD which is limited to 60 Hz input you will get an "out of range" or the likes of.

It's a Cypress CP-293. I have attached the pdf. Looks like it supports output of multiple resolutions.
My monitor is an LG 144hz 32iinch, so Vertical Frequency will not be an issue.
it doesn't specifically state that it supports 720x400 but I found a Youtube clip that shows this working.

If it doesn't work good enough (that's if I can fix it of course), I'll just get an OSSC.

That unit seems to have a lot in common with the Gefen VGA to HDMI scaler, the manual seems to indicate the same. If it's the same, quality should be really good. Try pressing the + and - buttons to reset the device. When not connected to power for a long time it sometimes outputs a signal that my display won't accept.

looks like Atlona AT-HD500 scaler clone (perfect device).

try to connect it to different monitor,

when I set a certain non-standard resolution, the monitor works with it, but the HDMI video capture device refuses to see the image

Imperious wrote:

The regulators outputs are all ok and none have any low resistances to ground. The 19.3 ohms is also across any capacitors on the 5v rail.

That being the case, the most likely culprit is that the main IC is shot. Not a lot you can do about that. There is also what looks like a ROM chip in that square socket, so it could be that... but you would probably spend more on an EEPROM burner, and possibly a replacement chip, than you would've spent on the converter at full price. That's assuming you can get a good copy of the ROM image.

I don't mean to be negative, but these sorts of devices are basically an I/O and power harness for the black box that is the main IC. If the harness isn't totally kaput, there isn't much left. IMO, you're tossing time and money into a pit replacing passives and hoping for signs of life. (Which is fine -- I've done it too, when the potential reward is worth it -- just don't spend more than you're willing to lose trying to resuscitate it.)

BTW, the OSSC cannot do framerate conversion either, it's just a line multiplier. So your display will have to support 70Hz either way. Personally, I haven't had much of a problem with format compatibility, although I'm using PC monitors and a single LG TV that seems to be fairly accommodating.

Thanks for the replies. I'm trying to fix this just to see how far I can get. So far I have identified what I thought to be an eeprom is in fact a Winbond/Nuvoton 78e365 Microcontroller.
I ended up removing the Fet then jumpering the 5v Across to the output. I spent ages figuring out where traces go which helped me identify certain parts of the circuit.
To cut a long and possibly boring story short the 22.1184mhz crystal on the Microcontroller does not work at all. I didn't realise at the time that my multimeter only reads frequency
up to 19.99mhz so after realising that I thought that the crystal was likely ok. All other crystals on the board are oscillating ok. I borrowed a 60mhz capable oscilloscope/meter from work
and proved the crystal is dead. I fitted a 16mhz one in there and that works ok but of course that's not the frequency it's supposed to be working at. I did manage to get some life from the
micro and could measure some activity on the address pins but no other life signs.
So at this point I have ordered some 22.1184mhz crystals from RS Components, so by the end of this week will know whether it works or not.