MegaSTE Repair Continued - Video Noise

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Re: MegaSTE Repair Continued - Video Noise

Post by exxos » Wed Jan 06, 2021 12:45 am

You can get noise on the black, my TV has it, but I've never seen noise like in the images posted before. I mean the blanking was there to turn off the electron beam originally while the gun moved to the top of the next frame, but that's a dead art these days with LCD screens. They don't really need blanking in that respect. But blanking is more borders now and wouldn't really be a issue in the main video.. As on my TV there is noise on the black, but its a cheap TV.. Its not really visible unless you really look for it.

But again the noise in the posted images looks to be a lot more than just normal background noise. Its unlikely to be picking up interference if your using shielded cables and a good PSU . it could be ground loop noise for example ... The problem with TVs can be they can be floating above ground by 100s of volts.. You then have a scan converter which I doubt is earthed, so you have a second floating ground ... The 3rd comes from the ST itself which is normally grounded.. So start to end, without some serious thick shielded cable with a good 0V core, you will get issues. The exact same issue happens with audio equipment.

Not saying this is your issue, but if you can run your rgb converter from battery, and even disconnect the GND pin on the ST power cord, it would help prove ( or not) if your dealing with a earthing problem or not. Its the only other reason I can think of which can cause bad noise like that, assuming its not just simple interference .
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Re: MegaSTE Repair Continued - Video Noise

Post by Tomswork » Wed Jan 06, 2021 12:49 am

That noise looks like an car ignition noise. Spark plug

Tom

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Re: MegaSTE Repair Continued - Video Noise

Post by exxos » Wed Jan 06, 2021 12:58 am

Tomswork wrote:
Wed Jan 06, 2021 12:49 am
That noise looks like an car ignition noise. Spark plug
I agree with that !
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Re: MegaSTE Repair Continued - Video Noise

Post by displaced » Wed Jan 06, 2021 1:15 am

I've had a voice at the back of my mind whispering 'grounding'...

I'll disconnect the earth temporarily on the PSU when I get a chance tomorrow!

I found that I could mostly hide the problem by reducing the OSSC's Pre-ADC Gain from 8 to 0, but then the overall picture was unnaturally dim.

I used a .PRG version of 50_60HZ and found a game (Xenon 2) that didn't insist on resetting to 50Hz. Noise is the same, and possibly worse due to the addition of some vertical waves.

Actually, just realised: the OSSC runs on 5V, so I should be able to run it from a USB battery pack. I've got one somewhere but it's a bit late to start making a racket trying to find the thing, so I'll give that a go tomorrow. I'm pretty sure you're on to something here!
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Re: MegaSTE Repair Continued - Video Noise

Post by displaced » Wed Jan 06, 2021 9:19 am

Well, poo.

Running the OSSC via battery doesn’t help. Had a good feelinng on that one, too.
6DE75F6C-AAAF-4AEA-B155-F89967C4D3A5.jpeg
6DE75F6C-AAAF-4AEA-B155-F89967C4D3A5.jpeg (203.3 KiB) Viewed 153 times
A bunch of Ataris and others:
Atari XEGS with RGB mod - STFM - Portfolio - Lynx Mk1 with McWill display - Mega STE - Falcon030 - Jaguar
Commodore VIC-20 CR with ClearVideo - CDTV (Wicher 8MB+IDE)
Acorn Electron - Archimedes A3020

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Re: MegaSTE Repair Continued - Video Noise

Post by exxos » Wed Jan 06, 2021 10:04 am

Looks like it made the noise worse ?
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Re: MegaSTE Repair Continued - Video Noise

Post by displaced » Wed Jan 06, 2021 10:51 am

That’s about right for Xenon 2 - the regularity and strength of the pattern varies. I’ll fire up I, Ball later for a direct comparison to before.

Very odd!
A bunch of Ataris and others:
Atari XEGS with RGB mod - STFM - Portfolio - Lynx Mk1 with McWill display - Mega STE - Falcon030 - Jaguar
Commodore VIC-20 CR with ClearVideo - CDTV (Wicher 8MB+IDE)
Acorn Electron - Archimedes A3020

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Re: MegaSTE Repair Continued - Video Noise

Post by rubber_jonnie » Wed Jan 06, 2021 3:09 pm

OK, one thing that might be of consideration here.

Have you got any long mains cables, gang sockets etc in play here?

Or even any other nearby devices that may have long power leads?

I've seen interference caused by these items before, so is it possible to relocate your machine to an area that is more 'electrically quiet' to see if it makes a difference?
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Re: MegaSTE Repair Continued - Video Noise

Post by rubber_jonnie » Wed Jan 06, 2021 3:23 pm

One more thing, I just tried Xenon 2 on my MSTE and the one thing that strikes me compared to yours, is that your screen is way brighter at the title screen, and the colours seem to be almost glowing, like it's too bright.

I'm assuming (I'm on my mobile so going back is difficult), that you've tried adjusting the contrast and brightness to see what difference it makes?
Collector of old Atari things:
800XL + Ultimate 1MB, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k +APE Warp) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg), 1040STF long button floppy, 2x 1040 STFMs + Gotek, 2x 4160STE with 32Mhz booster, ROM switcher, Mega ST1, Mega ST4, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
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Re: MegaSTE Repair Continued - Video Noise

Post by stephen_usher » Wed Jan 06, 2021 4:37 pm

I must admit that the picture does show it blooming out the highlights. Reducing the brightness and increasing the contrast would give a better picture.
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