Picture noise / bend help please..

[Mclaneinc]

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)

[Rybags]

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.

[+mytek]

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.

 

 

[Mclaneinc]

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..

[Rybags]

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.

[Mclaneinc]

Thanks Rybags will get a pack of resistors and tinker, the usual .25 watt ones ok?

[TGB1718]

1/4 W is fine, very low current circuit

[+mytek]

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.

 

[Mclaneinc]

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..

[TGB1718]

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.

 

[Mclaneinc]

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.

[TGB1718]

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

[Mclaneinc]

 

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

[Geister]

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.