Determining RGBS Sync Levels - Page 1
Forum section: electronics / beginners

author: Cj1
author_rank: Contributor
timestamp: May 26, 2024, 09:29:07 pm
content: I have an old LCD display (Toyota MFD) with an RGB input that i am trying to use as a monitor. I tried connecting a standard 75ohm RGBS signal to it but it did not sync, which makes me think the sync is non standard on this particular monitor.I bought a cheap scope and connected it to the sync line with a GPS device that i know will display a picture when connected to the monitor. However i am not quite sure how to interpret the results as i have never used a scope before.Here is a quick video, it looks like it stats at 0.7vpp and drops off or something. Am i doing this right?:https://imgur.com/a/VVNCdAb

author: Benta
author_rank: Super Contributor
timestamp: May 26, 2024, 10:20:07 pm
content: Your terminology is imprecise.What do you mean by RGBS? Is it four different signals/wires? In that case they're probably TTL level.Or do you mean CVBS (one wire)? In that case it's normally 1 VPP.

author: Cj1
author_rank: Contributor
timestamp: June 04, 2024, 02:03:40 am
content: Quote from: Benta on May 26, 2024, 10:20:07 pmYes, its is four different wires: red, green, blue & sync. I tried to use TTL sync, and it almost looks like it worked but not quite, as the picture was still rolling. It makes me think the signal is nonstandard but probably TTL like you suggested:https://imgur.com/a/CrF3EcPHow would i measure to find the correct sync?

author: Terry Bites
author_rank: Super Contributor
timestamp: June 05, 2024, 05:42:27 pm
content: Learn to use the trigger control and single shot on your scope.Your scope shows a 0.55Vpp signal and thats too low for most monitorswww.analog.com/en/resources/technical-articles/understanding-analog-video-signals.htmlRGBS is a scart thing. Where S is composite sync.Scart was designed by French satanists I belive.An RGB monitor normally will have H-Sync and V-sync inputs.You made need to separate these two signals out from C-sysnc, use an LM1881.Make sure to give it regulated volts, not car battery volts! Power it from a USB port or make up a simple regulator from a 78L05.

author: jzx
author_rank: Regular Contributor
timestamp: June 05, 2024, 06:22:12 pm
content: Quote from: Cj1 on June 04, 2024, 02:03:40 amIt seems that you can have a problem with the polarity of the signal. These green stripes must be the blanking intervals, and they have to be black.What is this picture? Has a black background?The scope picture is difficult to see, try to trigger well. It is the sync?If you want to connect something to the monitor you need to what levels it uses, and impedances. For a scart they are normally 1 Vpp, and 0.3 for sync, and 75 ohms, but if the sync is TTL, of course the levels are ttl. You can even have a monitor with TTL RGB, as and old CGA monitor, but it only show 8 color with only 3 bits, if you know the monitor shows more colors, it must be analogue.0.55 Vpp can be ok for the sync if you have measured unloaded because when you connect a 75 ohms load, the level will be half. If the signal on the scope is R, G or B, the level depends on the image, can be up to 1 Vpp or 2 unloaded, if it is scart.And the scan rates must be the same or almost for the monitor and the source.Quote from: Terry Bites on June 05, 2024, 05:42:27 pmScart was based on analogue TV sets, they have already the sync separator, so it was easier to use composite sync (and cheaper)

author: Cj1
author_rank: Contributor
timestamp: June 05, 2024, 06:53:32 pm
content: Quote from: Terry Bites on June 05, 2024, 05:42:27 pmI can assure you it uses a combined sync input as thats how the i was able to test the sync in the first place - with the navigation ecu connected. It is an RGB input with TX/RX lines for the AVC-LAN communications.I was using a game console to test with which does output an RGB signal through Scart, as its the only RGB device i have anyway. Good to know about the voltage though. I was thinking of using the schematic below to lower the signal level to 0.55, would this work?:csync (source) ---- R1 (8.2 kΩ) ----+----> csync (to display)|C (220 µF)|R2 (10 kΩ)|GNDWiring diagram for the MFD:https://imgur.com/a/AJcf8T1

author: Cj1
author_rank: Contributor
timestamp: June 05, 2024, 07:11:21 pm
content: Quote from: jzx on June 05, 2024, 06:22:12 pmThe picture has a green background normally:https://imgur.com/a/WruGDjXI measured the input of the monitor with a multimeter with nothing connected to it and it came out to 75ohm. However when i tried to connect a 75 ohm CSYNC signal i got a rolling picture. But it did have black bars like you describe, and looked more like what i am used to seeing when a monitor isnt syncing correctly. That slow green rolling picture is new to me.When i took the scope video i measured with the navigation ecu connected to the screen and everything was on. Im not sure how that would effect the signal. I had the scope attached to the Sync line.I recently read somewhere that this MFD screen, whilst accepting RGB and sync as its native format, also requires that they be strictly NTSC in timing, which means a horizontal frequency of 15.7Khz. The SNES i used to test with outputs 15.734 kHz, so im not sure if that would cause an issue.

author: jzx
author_rank: Regular Contributor
timestamp: June 07, 2024, 01:35:32 pm
content: 15.734 Hz is the official line frequency for ntsc, 15.7 must be an abreviation. Some screens have trouble with interlaced (or with non interlaced signals), the standard for ntsc TV is interlaced, but some consoles give non interlaced signal. (I dont know what does SNES).What is the model of the screen?