exxos's Atari, Amiga & retro forum

I'm having problems with getting an image through a SCART to HDMI scaler I bought to connect my Mega 4 to a monitor.

There is a faint image coming through, so I'm not sure whether it's the output, the SCART cable or the upscaler itself. Could it be that the scaler doesn't support RGB output? But what explains the faint image, as the Mega ST has no TV modulator and therefore no composite output?

I have verified that the output works using an older VGA upscaler I had, so I'm thinking it's either the cable or the converter that is not working correctly.

Maybe your cable has some series resistors in the RGB lines and its dropping the RGB voltages to much ?

Yes I measured the resistance to 150 ohms on the rgb pins and around 75~80 on the csync.

I've seen designs recommending up to 330 ohms on the sync pin on machines without a modulator.

keli wrote: ↑Fri Oct 06, 2017 7:39 pm Yes I measured the resistance to 150 ohms on the rgb pins and around 75~80 on the csync.

I've seen designs recommending up to 330 ohms on the sync pin on machines without a modulator.

Can't remember what I used on my cable, but I got one off ebay ages ago also as a spare, think it had over 100R on the RGB, and I could hardly see the image on my LCD. I just took them out in the end. I would try 68R. Or just solder over the RGB resistors at least and see what happens.

EDIT, looked at my cable, 68R in the RGB lines, also got 2 ceramics elsewhere, can't remember why, must be 100pF. Don't see any resistors elsewhere.

After switching out resistors and adding caps to my cable without luck I finally opened up the converter.

Turns out the pins for red, green, and blue are not connected to anything. I could find three short traces that ended in unpopulated headers for resistors, so there was no electrical connection.

Seems my scart converter only supports composite input, which is a weird decision, as the box does have a VGA port as well.

Additionally the VGA port only supports higher resolutions, which again is odd since the box is fully capable of supporting the lower resolutions over the composite input.

It's a pity it doesn't work, as the converter is otherwise very well built.

Some of those cheap HDMI scalers only support composite output. I have one like this:

https://www.konigelectronic.com/audio-v ... -550581465

These support RGB SCART input and they also have an upscaler. It scales up to full HD.

redhawk668 wrote: ↑Tue Feb 13, 2018 10:48 pm Some of those cheap HDMI scalers only support composite output. I have one like this:

https://www.konigelectronic.com/audio-v ... -550581465

These support RGB SCART input and they also have an upscaler. It scales up to full HD.

Yes that's the conclusion I came to. Which is annoying, as the scaler does support RGB, albeit only via a dedicated VGA input... The VGA input however does not support the 15KHz signal coming from the ST, even though that's what the (composite-only) SCART input supports.

I ended up chaining a RGB->VGA scaler I had with the HDMI converter. A suboptimal solution, but I didn't want to spend too much on buying converters hoping they'll work. I may take a look at the one you posted however, thanks.

Well, I can say it works very nicely. I even use it with the output of a composite modded ZX Spectrum and that is very usable too. I can definitely recommend this scaler.