Mclaneinc Posted January 22, 2020 Share Posted January 22, 2020 A little OT as it not just an Atari question but I hope no one minds.. Using and RGB connection on my old Amiga (Phillips make) monitor and I have the situation where on a bight white screen you get a buzz until its off that screen, I'm also getting a picture distortion at the top on the same screen. I seem to remember that this means the signal needs attenuating, so is this just a case of adding a resistor in line on the RGB lines in the scart? If yes, are there any values that are a good guide? The comp also has noise on a white screen via the atari but its hardly noticeable whereas the RGB is a proper buzz...(only on ultra bright white screen) Quote Link to comment Share on other sites More sharing options...
Rybags Posted January 23, 2020 Share Posted January 23, 2020 I bought an RGB to SVideo converter for VBXE and it's accepted inputs were less than the peak to peak range of VBXE - I didn't try it first to see if it'd be OK. What I did and what you'd probably need too is a voltage divider on each R, G, B pin. Fitting that inside a SCART plug could be a problem. Voltage divider needs 2 resistors per wire - the maths is fairly simple, generally you use a big value on the one that goes to GND and a little one on the passthrough one. Quote Link to comment Share on other sites More sharing options...
+mytek Posted January 23, 2020 Share Posted January 23, 2020 If the monitor already has termination resistors to ground built-in (and many do), all you'll need is series resistors coming out of your video source, preferably before feeding into the video cable. When looking at the diagram below, normally we are talking about 75 ohm series resistor (ZS) - feeding into a cable with 75 ohm impedance (ZO) - and then 75 ohms to ground (ZL) at the monitor side (this forms a voltage divider as well as serves to match impedance). However the actual value that works best for you, might be either higher or lower dependent on what the signal source is. So some experimentation might be required. If your monitor doesn't have internal resistors to ground, that might be the first thing you would want to try. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted January 23, 2020 Author Share Posted January 23, 2020 Ack, trying not to touch the monitor, was hoping to just mod the lead...Still got my 1050 to sort as well, been playing about with a Teensey microcontroller board which socking worked after my first soldering in MANY years but boy was the work small..Have to admit to using a magnifying light, glasses and eyesight just didn't cut it on connections that small. Not sure what to do re the monitor, may just drop the brightness down and suffer that as with less brightness the nose and screen tug goes (well is almost not noticeable). As always, THANK YOU for your help, as said, was hoping I could just mod the lead......Oh well.....I owe you one.. Quote Link to comment Share on other sites More sharing options...
Rybags Posted January 23, 2020 Share Posted January 23, 2020 If the monitor is terminated as he describes then I would surmise that simply placing some low value resistors in series on the cable would complete a voltage divider, with no need to modify the monitor at all. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted January 23, 2020 Author Share Posted January 23, 2020 Thanks Rybags will get a pack of resistors and tinker, the usual .25 watt ones ok? Quote Link to comment Share on other sites More sharing options...
TGB1718 Posted January 23, 2020 Share Posted January 23, 2020 1/4 W is fine, very low current circuit Quote Link to comment Share on other sites More sharing options...
+mytek Posted January 23, 2020 Share Posted January 23, 2020 3 hours ago, Mclaneinc said: Ack, trying not to touch the monitor, was hoping to just mod the lead... Even if your monitor doesn't have internal terminating resistors (or a switch to kick them in, as some monitors do). those resistors can be added external from the monitor, and hidden inside the housing of whatever connectors you are using (probably RCA, BNC, or otherwise). Quote As always, THANK YOU for your help, as said, was hoping I could just mod the lead......Oh well.....I owe you one.. Not sure if that's directed towards me, but I'm always glad to help when I'm familiar with the problem. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted January 23, 2020 Author Share Posted January 23, 2020 Was meant for everyone so definitely you I'm always super impressed with the level of help people give in here, the only time people don't get an answer is when there is no known one but usually someone explain that as well As said, will get some resistors and see what difference it makes, its a real tiny problem but when you get the big bright screen and there's a buzz its a bit annoying...Hardly the end of the world but as its a crt I don't want to aid in the tube going soft bt over driving it as well.. 1 Quote Link to comment Share on other sites More sharing options...
TGB1718 Posted January 24, 2020 Share Posted January 24, 2020 just a thought, have you another cable to try, buzz and screen noise can be caused by inadequate screening in the cable, maybe have a look and make sure the ground joints are good. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted January 24, 2020 Author Share Posted January 24, 2020 Will do but no extra cable to try which I need to remedy (always have a spare!) Most cables I've seen these days have no screening at all, not even the very mild armour screen that old multicore cable came with. Quote Link to comment Share on other sites More sharing options...
TGB1718 Posted January 24, 2020 Share Posted January 24, 2020 46 minutes ago, Mclaneinc said: Will do but no extra cable to try which I need to remedy (always have a spare!) Most cables I've seen these days have no screening at all, not even the very mild armour screen that old multicore cable came with. One reason I always make my own cables, plugs and suitable cables are cheap on ebay, then at least you know what you've got. Recently made an S-Video cable and it works a treat Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted January 24, 2020 Author Share Posted January 24, 2020 Don't blame you, now that my parkside soldering station is out of retirement and I got some .4 gauge solder I'll be doing that sort of thing myself (well already started with a microcontroller based send cable for my snes). New glasses deffo needed Quote Link to comment Share on other sites More sharing options...
Geister Posted January 26, 2020 Share Posted January 26, 2020 If you've got to my age and the eyes are getting cataracts, maybe cataract surgery will help. I had the surgery last year and the difference was amazing. It's like I had a pair of brown filters on my glasses making everything darker and crap colored. After surgery, I was able to go back to an older prescription on my glasses and colors are brilliant again! I feel like I have 20 year old eyes. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.