STE video issues - dot crawl & wobble issues & ghosting

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STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Nov 17, 2015 6:14 pm

Starting from the beginning... the STF's for example had bad "dot crawl" problems, this was "fixed" on the STFM's and had a small capacitor preset to "tune it out", or lock the image so the dot crawl doesn't happen.

However, on the STE, this problem seems to be back. I noticed the problem varies a fair bit depending on the actual 5V voltage. At about 4.8V the wobble is very slow. This is visible on the vertical edges of icons and the edge of the desktop screen. The higher the voltage goes (5V and up) the wobble gets really fast, but the dot crawl seems to settle down a bit more. The green desktop colour looks like its moving diagonally to the right like bad interference.

It is possible once the metal shielding is in place the problem may simply go away, but I wonder if anyone else has noticed this problem, or investigated it already ?

I've uploaded a video of it. It mostly shows up in medium res, low res doesn't seem to be effected as much, or very little.

http://exxoshost.co.uk/temp/STE_DOT.MOV

Look at the green background, there are clumps of darker areas scrolling up the screen.. The speed they go seems to vary from still to pretty fast. Like something is "drifting" in the video circuit somewhere.
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Nov 17, 2015 10:26 pm

While doing some probing, I found that on power up (TOS206) then the Atari fuji appears, there was faint ghosting across the screen. Turns out adding more capacitance to C411 solved that issue. So defiantly a mod worth doing. This capacitor is located just under the right side of the PSU.

BEFORE
before.jpg


AFTER
after.jpg


For those who can't see any difference.. then.. nevermind.. :lol:

The "rolling" distortions in the image have stopped and turned into more vertical lines which I think is the same as on my STFM. So this could be monitor or cable related now...
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby spiny » Wed Nov 18, 2015 9:57 am

By 'adding more capacitace' do you mean replacing the cap with a higher value ? If so, what would you suggest ? :)

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Wed Nov 18, 2015 10:11 am

spiny wrote:By 'adding more capacitace' do you mean replacing the cap with a higher value ? If so, what would you suggest ? :)


Well I stuck on a 2200uf over the top of it, simple because that capacitor was next to me at the time :lol: The capacitor on the motherboard is very low value, 0.47uF. I suspect 10uf - 100uF would be in the area of overkill. but with ceramics pushing over 1uF these days, one of those would probably be best. I will give it a try later see what happens...
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Wed Nov 18, 2015 8:41 pm

spiny wrote:By 'adding more capacitace' do you mean replacing the cap with a higher value ? If so, what would you suggest ? :)


1uF ceramic doesn't fully solve the ghosting problem.

10uF electrolytic probably 95% solves the problem.

47uF seems to work best, may improve a couple % with the 1uF in addition.

DSCN2533sm.JPG


The "dot crawl" seems to show up on RF more than anything.. Still not really sure what's causing it.

http://exxoshost.co.uk/temp/RF.MOV
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Wed Nov 18, 2015 10:54 pm

monochrome shows the problem up pretty well... I think its inteferrences on the RGB lines. I think I posted somewhere that I had seen similar issues on the STFM. So I wonder if anyone else can confirm they see this or not on a LCD screen ?

dist.jpg
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby punkrulesok » Thu Nov 19, 2015 8:25 pm

Is this possibly down to age of Hardware and Monitor? I don't recall this issue back in the day, and the Atari Monitors were specifically really good, black and in focus

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby spiny » Thu Nov 19, 2015 9:27 pm

Just did this on one of my STes and to be honest, I can't see a difference :)

however I am using the SVIDEO mod with an LCD TV, so the picture is reasonably good already.

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Thu Nov 19, 2015 9:51 pm

I'm using RGB/scart so you would need to use that to see the changes. RF I get bad dot crawl. It seems to do that on a few STE's I've tried. Its possible it could be the monitor or cable. I've got a mono monitor in loft so might drag that down to try when I get chance. Might also try hooking up to the larger TV in the living room to see what happens on there. You probably would need RGB to get a clear image in the first place to see if there is a fault there or not.
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Sun Dec 06, 2015 11:23 am

As a side note, I hooked up my STFM and the video seems fine on that one. But not on my STE. So I am going to try a different cable, though its only "overall screened" from retrocables :( I think the issue is likely to be on the STE video circuit somewhere. But no time to look into this currently. What I want to try is a totally screened cable to see if it improves the video any, but again its not high up on my to do list at the moment.
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby fenarinarsa » Mon Jan 04, 2016 11:36 pm

My STe always had this kind of video interferences on the RGB output. I might give it a try, thanks for the fix :)

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Jan 05, 2016 1:11 am

fenarinarsa wrote:My STe always had this kind of video interferences on the RGB output. I might give it a try, thanks for the fix :)


I still need to do more tests but I suspect its the cable and/or monitor mostly, though the "fix" is worth doing if your using RGB. It improved the image no end for me.

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Mar 29, 2016 7:13 pm

Been servicing a STE for someone today and seen bad video ghosting once again. So here are the before and after images.

You can see on the first image the "black streaks" across the screen. Even ghosting black areas from the icons.

ghost1.jpg



As found before, with a cap mod, the video is much improved.

fixed.jpg
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby Atari030 » Tue Mar 29, 2016 10:23 pm

exxos wrote:monochrome shows the problem up pretty well... I think its inteferrences on the RGB lines. I think I posted somewhere that I had seen similar issues on the STFM. So I wonder if anyone else can confirm they see this or not on a LCD screen ?

dist.jpg


Chris, My MegaSTE does this on the NEC LCD I have (probably the others too). I put it down to needing a resistor on the RGB lines but haven't done it yet. I wondered if the reason TOS 2-3-4 introduced the desktop patterns was so you can hide this. :-) It is only really obvious with a solid desktop pattern.

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Mar 29, 2016 10:30 pm

Atari030 wrote:Chris, My MegaSTE does this on the NEC LCD I have (probably the others too). I put it down to needing a resistor on the RGB lines but haven't done it yet. I wondered if the reason TOS 2-3-4 introduced the desktop patterns was so you can hide this. :-) It is only really obvious with a solid desktop pattern.


Its been on my "to do list" to check on the resistors in the cable. I keep meaning to try it, will try and investigate it soon.

Video circuit is very sensitive to noise. I never had a MSTE so can't investigate it :)

The supposed "fault" is the vertical pattens in the title/drag bar on the gem window.. thats what I have yet to solve, though I think its a issue with the monitor rather than the STE.
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby Atari030 » Tue Mar 29, 2016 10:35 pm

Back in my early STFM days I noticed a LOT of machines had big trouble with sync with monitors like the Commodore 1802. Desktops were all over the shop but games ran OK. From that point I was more convinced that the ST's had inherent design flaws. Funny thing is I never saw that problem with STE's, same cable, same monitor, no problem. I guess LCD's are just less forgiving.

If I get the chance I'll try attenuating the cable this weekend.

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Tue Mar 29, 2016 10:39 pm

Atari030 wrote:Back in my early STFM days I noticed a LOT of machines had big trouble with sync with monitors like the Commodore 1802. Desktops were all over the shop but games ran OK. From that point I was more convinced that the ST's had inherent design flaws. Funny thing is I never saw that problem with STE's, same cable, same monitor, no problem. I guess LCD's are just less forgiving.

If I get the chance I'll try attenuating the cable this weekend.


I use a cheap Alba LCD and don't really have any troubles with it on STFM and STE. Though I have noticed the image jumping to the right then left, though that seems to be bad regulation on the shifter. It would mostly jump after a reset but settle down generally after that anyway.
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby Atari030 » Wed Mar 30, 2016 2:03 am

I have a 1702 I'll drag out one day and hook up composite and see if I can capture it going nasty with one of my FM's. It has been a while since I used on. :-)

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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby thgill » Wed Mar 30, 2016 4:12 am

Holy hell, i can't believe I missed this thread before. I have been bitching about this same issue for several years. I have had 5 or 6 NTSC and PAL 520 and 1040 STEs and they have all exhibited this issue.

I'll take apart my current PAL machine this week and see how well this works.

Excellent!!
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby thgill » Thu Mar 31, 2016 4:03 am

Success!

Installed a 220uF cap across C411 as per exxos's directions above and the ghosting was all but 100% eliminated.

Image



sorry, no before and after screenshots of the ghosting, but exxos's pictures earlier in the thread pretty clearly show the effect this has.


This makes me very happy.

:cheers:
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby exxos » Thu Mar 31, 2016 7:33 am

thgill wrote:Success!
Installed a 220uF cap across C411 as per exxos's directions above and the ghosting was all but 100% eliminated.
sorry, no before and after screenshots of the ghosting, but exxos's pictures earlier in the thread pretty clearly show the effect this has.
This makes me very happy.
:cheers:


Awesome , thanks for the report back! :cheers:
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Re: STE video issues - dot crawl & wobble issues & ghosting

Postby thgill » Fri Apr 01, 2016 3:06 am

This wonderful little fix info should definitely go in a wiki somewhere.
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