SCART to converter - Page 1
Forum section: electronics / beginners

author: msknight
author_rank: Regular Contributor
timestamp: August 02, 2021, 02:45:16 pm
content: I'm checking this, before I go doing something stupid.Source machine - NMS 8250 - Destination, SCART to HDMI converter.https://en.wikipedia.org/wiki/NMS-8250-https://www.ebay.co.uk/itm/265028020602Signal should be RGB, but is very dim and distant only just about visible to the human eye.Putting a multimeter across pin 16 to the outer shield (which I believe is electrical ground) gives 0.111V which is below the trigger threshold of 1 to 3V for RGB.So I'm checking, before I go cutting into things and injecting voltages into lines and potentially blowing something up.My brain is thinking... if the trigger voltage is below the 1v threshold, then fair enough. But if that's the case then why is the TV working fine? ... or is it because the TV is taking a component signal and not the RGB.... and the SCART to HDMI converter just can't handle the component signal?Someone must have come across this before and there should be an easy solution. If not, then I'm thinking that the easiest solution might be to open up the Scart to HDMI converter and use its own power supply to connect straight to its own pin 16 internally to drive it high.(it works off a 5v DC input, so it must be straightforward to cable it via a resistor - and disconnect the pin from the actual socket so I don't send power back down the wire into the MSX2)Grateful for wisdom and thoughts please, before I go blow something up.

author: msknight
author_rank: Regular Contributor
timestamp: August 02, 2021, 03:02:27 pm
content: Errr.... I double checked my measurements and it's putting 3.22v on line 16.Now I'm confused. Is 3.22 too high? Should I try and fool the converter anyway?

author: Benta
author_rank: Super Contributor
timestamp: August 02, 2021, 03:34:13 pm
content: You need to:Measure the signal between 17 and 19,this is composite video signal and ground. Don't use the shield for ground.this is sync output and should be 0.3 Vpp. Corrected after I noticed that it's a NMS-8250 which doesn't have CVBS out, but only sync.Terminate the signal with a 75-ohm resistor between 17 and 19.Only in this way will you see the correct voltage level.

author: msknight
author_rank: Regular Contributor
timestamp: August 02, 2021, 04:10:29 pm
content: There appears to be nothing between 17 and 19.I take it that the MSX2 is only outputting RGB and not composite or component ? Do I have that right?

author: Benta
author_rank: Super Contributor
timestamp: August 02, 2021, 05:04:13 pm
content: From what I can find, it's only outputting RGB, which means pin 16 should be around 3 V.If you see nothing on the CVBS/Sync output, it's remotely possible that the green output contains the sync.

author: msknight
author_rank: Regular Contributor
timestamp: August 02, 2021, 09:00:00 pm
content: That's looking highly probable.But it leaves the question as to why the TV can handle it and the converters can't. And even then... what can I do about it?

author: Benta
author_rank: Super Contributor
timestamp: August 02, 2021, 09:12:30 pm
content: Quote from: msknight on August 02, 2021, 09:00:00 pmNothing. You've apparently overlooked the word "Composite" in both headline and description of the product on eBay.