MegaSTE Repair Continued - Video Noise

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rubber_jonnie
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Re: MegaSTE Repair Continued - Video Noise

Post by rubber_jonnie » Thu Dec 31, 2020 10:12 am

Interesting, your scope looks very much like mine :)

That aside, I'm also an amateur, so I know what it's like trying to chase down these things!

It might be worth having a close look at the schematics, and working back from the socket to the shifter and beyond to see what points there are where interference can be picked up. I'm surprised that the caps suggested by exxos had no effect, but what I would say is that it does look like the banding on the old Spectrums et al that was caused by poor filtering, I think on the power to the RAM.

I know it's not quite the same, but it may well be worth testing by adding additional filtering to the RAM power lines, and considering a more general re-cap of the board. Generally the caps do seem to be ok on Atari's though. Are you in a position to try with a different PSU? Or a bench PSU to see if that eliminates the problem?

A couple of other things. Have you checked the video socket and reflowed? Have you tried another video cable?

Finally, I'm not sure what other video options the MSTE has (I only ever use mine on VGA), but it may be worth checking what your options are, such as SCART and composite to see what the results are like there. I think you also mentioned you use an OSSC, and I have found that some things pick up weird interference problems when I use mine, so I have a select group of items that I pump through it. It would be worth trying to use it without the OSSC to see if that makes a difference.
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 :)
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Re: MegaSTE Repair Continued - Video Noise

Post by rubber_jonnie » Thu Dec 31, 2020 10:15 am

exxos wrote:
Thu Dec 31, 2020 10:02 am
Odd.. Have you ran YAART to test the ram ?
BTW if you're going to YAART it make sure that you have nothing like ACCs or anything loaded as it can cause YAART to show errors when there are none. I forgot this the other day and got hundreds of errors, which turned out to be a false positive.

BTW, does the problem improve/get worse over time?
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...
www.electronicnothingness.co.uk

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Re: MegaSTE Repair Continued - Video Noise

Post by exxos » Thu Dec 31, 2020 10:22 am

Ah yep. As @rubber_jonnie says, you should be using scarr rgb for testing. Its just possible the ossc is to sensitive to noise and actually creating the problem.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: MegaSTE Repair Continued - Video Noise

Post by displaced » Thu Dec 31, 2020 11:03 am

Thanks for the replies! Definitely gives me some stuff to try!

Yep, I’ve run YAART for an extended amount of time - got up to 49 passes on 4MB with no errors detected. Should also count my luck that the machine is otherwise very stable.

I’ll have a root around for another power supply a I’ve got a PicoPSU somewhere - I think those have -12V?

Interesting thought re filtering around the RAM. There’s definitely a relationship between bus activity and severity. It’s barely noticeable when resting at the desktop, but goes nuts during the We Were @ demo.

Have reflowed the video socket, tried two different ST-to-VGA adaptors, and different VGA cables.

I too have begun giving my OSSC the side-eye in all of this. It’s not been an issue with any other machine, but there’s always a first! I’m a bit limited on display options - not even got any SCART-capable TVs any more. But I have an old Dell monitor with composite and a basic SCART-to-HDMI converter that I used to switch everything through before getting the OSSC. I doubt it’ll give a good picture, but it’ll at least show if this particular interference remains across different adaptors, thus putting the blame back on the MSTE.

The interference is there from a cold start and doesn’t change over time/temperature.
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 displaced » Fri Jan 01, 2021 3:21 pm

Happy new year, everyone!

I'm still trying to figure out where I've put the Dell with the composite input so I can test without the OSSC, but in the meantime I've been having a look at PSUs. I'd overlooked that the MSTE wants -5V which my Pico doesn't provide - and I'm not sure I want to mess about with getting -5 via another line on it.

I was thinking -- if I got something that would power the MSTE, I could swap it in to see if it helps with my problem. If it doesn't, I've still got a nice PSU to use elsewhere.

I'm gonna go for the Meanwell RQ-85B. Meets or exceeds the stock PSU's ratings at each voltage and is physically a little smaller than the original. (edit: forgot to link to its specs: https://www.meanwell.com/webapp/product ... prod=RQ-85)

Does anyone happen to know the part number for the MSTE's motherboard power connector? I can see it's the same pinout as the P8/P9 combination on an AT supply, but the two AT connectors look quite different to the MSTE's... unless it'll still physically connect despite being different!
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 geogeo_28 » Tue Jan 05, 2021 11:14 pm

Not sure if this is related but I have a similar issue with my Atari STE PAL:
IMG_0392.jpeg
IMG_0392.jpeg (82.25 KiB) Viewed 110 times
I am using a XRGB Framemeister for upscaling with a VGA To SCART converter which convert HVSync to CSync.

Same setup with my Atari STF NTSC and no noise.
The Atari STE has a new PSU, recapped, the mod to fix video ghosting.

I can workaround this noise but changing the black level and the brightness in the color settings of the Framemeister. Not sure if you can change the black level on your TV?

I will take a look with the diagnostic cartridge and see if the video frequency (PAL vs NTSC) has an impact.

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Re: MegaSTE Repair Continued - Video Noise

Post by exxos » Tue Jan 05, 2021 11:29 pm

Is if the PSU good for all these scan converters ? It looks more like digital noise being generated, which would be normally nothing to do with the ST itself.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: MegaSTE Repair Continued - Video Noise

Post by geogeo_28 » Tue Jan 05, 2021 11:35 pm

Comparing 50Hz vs 60Hz.
On Atari STE and Atari STF at 60Hz NTSC the signal is clean, no video noise.
At 50 Hz PAL on both machines I have video noise. The noise is different on the Atari STF but visible.

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Re: MegaSTE Repair Continued - Video Noise

Post by displaced » Wed Jan 06, 2021 12:05 am

It does look very similar indeed - mine's also a PAL machine, running in the UK (so no voltage converters or whatever).

My OSSC's PSU would seem to be fine - no similar interference on the other machines I run through it (STFM, VIC20, XEGS, CDTV). Still haven't found that Dell with composite input which I know is around here somewhere to test without the OSSC - probably a job for the weekend.

My interference is definitely activity-related. For example, I've got Rainbow Islands' attract screen running right now. At the title and credits screens, there's virtually zero interference. Then there's a burst just as the level fades in and it stays around whilst the game plays itself.

I can do some tinkering with the OSSC... and if testing with composite doesn't show the issue I'll happily scowl at the OSSC and tweak it to hide the problem!

When you say 'recapped', do you mean the whole motherboard? I've got a suitable Meanwell PSU on its way, which I'll happily use as a spare if it doesn't actually help with the problem. So after that, recapping the motherboard was the last thing I could think of to try!

I was also wondering if the ST-to-VGA thing I was using could be a problem, but I'm guessing you're using a plain 13 pin DIN to SCART lead and still have the problem?

(just saw your new post re freqs. Hmmm! Interesting that you get this on your STF too, whilst my PAL FM looks absolutely fine)
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 geogeo_28 » Wed Jan 06, 2021 12:27 am

displaced wrote:
Wed Jan 06, 2021 12:05 am
It does look very similar indeed - mine's also a PAL machine, running in the UK (so no voltage converters or whatever).
Not sure if you can switch to 60 Hz and see how it goes?
Using the following program prior to run the game: http://www.atarimania.com/utility-atari ... 33144.html
displaced wrote:
Wed Jan 06, 2021 12:05 am
When you say 'recapped', do you mean the whole motherboard? I've got a suitable Meanwell PSU on its way, which I'll happily use as a spare if it doesn't actually help with the problem. So after that, recapping the motherboard was the last thing I could think of to try!
The whole motherboard is recapped. Recapping the motherboard in your case is definitely something to try.
displaced wrote:
Wed Jan 06, 2021 12:05 am
I was also wondering if the ST-to-VGA thing I was using could be a problem, but I'm guessing you're using a plain 13 pin DIN to SCART lead and still have the problem?
Same issue with 13 pin DIN to SCART.

Definitely on my side the issue is digital noise as Exxos pointed out and I suspect an incorrect Black Level for PAL on my TV or elsewhere: https://en.wikipedia.org/wiki/Black_level

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