Vertical white stripes when using a ST to VGA cable

[marcello]

I bought a ST to VGA adapter so I could play low-res games on a flat display, but no matter the resolution, low, mid or high, I have annoying vertical white stripes which kind of denature the gaming experience.


This is the picture I get when using Xenon II in low res, and Uniterm im High Res.
https://imgur.com/a/rrtdlew
https://imgur.com/a/pA8iwzB

What could be the cause of this ?

I was wondering if electronic interferences could cause this because the cable is quite long.
This is the cable I am using: http://www.best-electronics-ca.com/monadapt.htm

Some notes:
* switching monitor did not help
* I have also a Video Scaler Box from Ambery that I tried to put in the chain, output is similar

[ctirad]

This kind of noise is usualy caused by a signal disturbance from the mains caused by either a ground loop, or weak capacitors in ST PSU, or both. I'd also check the cable for a proper impedance on RGB lines and termination.

[marcello]

Thanks, I read a bit about what are ground loop, will see if I can avoid that, then look into a replacement PSU.

[Smonson]

Are those lines spaced exactly every 16 pixels?

To me that doesn't look like mains interference - the signal is approx 500KHz, and is exactly synchronised to the video. To me it looks like the interference is digital in origin. If you have an STFM it may be worthwhile to check that all the ICs are properly plugged into their sockets. I'd definitely look into replacing the capacitors though, it's a common problem for video.

[ctirad]

Thanks, I read a bit about what are ground loop, will see if I can avoid that, then look into a replacement PSU.

You need only to replace the electrolytic capcaitors, not the whole PSU.

[marcello]

@Smonsom: I counted 20 of those line in middle and low res, which would then bring to a perfect 16 pixels distance (320 / 20 )

Which calculation did you use to come to the 16 pixels ? Curious here, but I am bit of a noob in electronics.
The machine in question is a STE. I changed the TOS roms one year ago, but I was only using High Res before that and did not notice these stripes in High Res.

[Smonson]

In low res mode, the shifter outputs pixels at 8MHz, same as the CPU clock speed, so 500KHz is every 16 pixels. At 50Hz, the length of each scanline is an exact multiple of 16 pixels (512 = 320 for the normal video plus 192 for borders). It's not exact in 60Hz though - I think you'd get diagonal lines if you were to try that mode. It is exact in 71Hz: 896 pixels = 224 clock cycles (it produces pixels at 32MHz) = 14 x 16 clock cycles.

The ST has a 500KHz clock that is needed by the keyboard and MIDI serial interfaces, as well as other clocks that are all multiples of 500KHz (2MHz, 4MHz, 8MHz, 16MHz and 32MHz). Cyclic current draws aligned with these clocks could generate noise, and if capacitors that are there to keep voltages steady during cyclic current draws have lost their abilities over the years, you can get these types of signals in the video... Or at least that's my only theory.

Electrolytic capacitors have a limited life since contain a liquid, which dries out. But they are cheap and easy to replace, having only two legs.

[marcello]

Very clear, thanks for the detailed explication, made my day !

[Smonson]

It's always a pleasure if I can assist in fixing something!

[marcello]

So I replugged ROMs and keyboard IC in their socket.
I had a look at the PSU at the capacitors look quite new, isn't that old capacitors have a curved top when they get old ?

Since this STE is second hand, I wonder if the previous owner changed the capacitors already

Picture of the PSU
https://imgur.com/a/etldwpC

[mpattonm]

no, they are not changed.

[dhedberg]

I had a look at the PSU at the capacitors look quite new, isn't that old capacitors have a curved top when they get old ?

An electrolytic capacitor can be bad without a bulging vent.

[marcello]

no, they are not changed.

I know there would be people on this forum able to spot this

[Mq666]

Did you fix that vertical stripes? I have exactly the same effect in 520STM I bought recently. So I'm thinking what I can try to do.
Did you replace some capacitors? Which exactly to try: rather in video circuit or in digital circuits?

[marcello]

I haven't found a solution yet because I've been too lazy to change the PSU.
Why I don't understand is by using the Atari SM124 CRT, the build is absolutely perfect and crystal clear. I *love* that display !
Also using a RGB SCART connector on a flat screeen, I have none of these vertical stripes, although a different graphic glich appear, certain color flicker.

Now using the BenQ BL702A which is 15KHz compatible display, and the Ambery VGA converter, I always have the vertical white stripes ( like on first post) . It is damned ugly on some games like Another World, but acceptable most of the time.

So if this a problem from the mains, why would it happen only when using VGA ?

[Smonson]

Possibly the BenQ display places a greater load on the RGB lines, causing the voltage to sag.

[manicx]

It's being a loooong time since I last posted here so I am happy to see the place thriving.

I recently starting setting my retro corner in my flat including my beloved STE. It's a 520 STE with 4MB RAM (In glorious SIP modules) rev CA4003290. Unfortunately, I used to hook it on a 14" CRT TV that I don't have anymore so it I decided to get a ST2VGA r4 from centuriotech and a GOEX drive since I don't have a PC with a FDD. The monitor I used is a BenQ BL702A.

Everything works fine EXCEPT the problem described before with the vertical stripes. As described, I don't get this problem if I connect it to an ancient 24" CRT and also, and here comes the strange thing, if I boot into TOS. In TOS, either low,mid,high, the picture is fine.

I am wondering what causes this problem. If it was greater load on RGB lines, wouldn't be visible everywhere including in TOS? Also, if it was the capacitors, I understand that it would be visible in CRT too. Any ideas?

The same monitor seems to operate just fine when connected to an Amiga 4000 in most resolutions.

[pawaller]

I have exactly the same issue on a 1040 SFM that I just picked up.
Tos is fine but games look terrible.

're-capped the psu but made no difference

Phil

[Emunerd]

I'm having the same issue like in those screenshots. I have an Atari 520 STm and have it hooked up with a
"Atari ST/STe video monitor RGB DIN13 to VGA adapter adaptor for 15kHz monitors"
To a "Monitor Benq 17" BL702A LED 15kHz compatible Commodore Amiga Atari DB23 VGA"

I don't see these vertical lines in the bright white/green GEM, but even from the start I saw faint flickering effects at the edges of texts and icons. Didn't like it, but if that was all I could settle for it. But oh boy who ugly it got when I loaded up Dungeon Master! Lines, lines, lines..!

It's not like they don't exist in TOS, they're just hidden against the backdrop. I've tried 30+ games now, and its visibility really depends on the game's coloring scheme and brightness. One game crashed back to TOS giving GEM a dark purple color and the lines where very much visible.

So I messaged the seller I bought the VGA adapter from and here's my inqury with his response:

--
Hi. I'm experiencing vertical lines on my monitor through this adapter.

It's near invisible on the GEM desktop with its white borders and green backdrop. In different envrionments such as black and grey, it's very prominent.

I have it connected to an Atari STm with a BenQ BL702A LED 15kHz monitor. I've tried using a different VGA cable and also tested the monitor with a PC, for which it it had a clear picture.

Connecting the Atari to an LCD display with its RF modulator does not produce these vertical lines.

Do you know of anything I could check and troubleshoot to correct the issue?
Thanks.
--

--
Hi,

You will need to adjust the 'Phase' setting (may be called something else), it is usually found in the menu with the horizontal and vertical size adjustments. As you have noticed the effect of it being slightly out is more noticeable in certain graphics modes/ colour combinations than others. It will most likely never be perfect so you may need to experiment a little to find a good compromise.

Cheers

Rich
--

I spent a while going through the phase of adjusting it as good as it could get. There was a sweet spot where the lines weren't as flickery and visible.

So that's that.. that's just not good enough. I've taken advice from someone in this thread regarding the PSU. I have the old external unit which is glued together so I can't as easily re-cap it without a hacksaw, but there's a new modern make on ebay so I'll get that and provide an update after it's been put to use.

[Smonson]

I've been seeing this a lot on my own setup too since I started a project that uses an analogue monitor too... I now think the phase setting is the answer. I too can't get a perfect image using only the monitor's phase controls. The problem is that the monitor samples the pixels at a certain rate, and that rate doesn't correspond to the ST's pixel generation clock. The ST's modes are weird compared with industry standards. For a mode detected as "640x480" the monitor is expecting around 800 pixels per scanline, not 1032, and the horizontal stretch adjustment doesn't usually go far enough to bring them into alignment. The vertical bars are the moments between pixels where the shifter is changing from one signal level to another. Even if the colour is the same there is a flicker of noise.

[Emunerd]

I just wanted to leave a last update where I recently got a brand new PSU for my 520ST, and the vertical stripes are still ever present. I guess from what information that has surfaced regarding this issue I shouldn't have expected otherwise. The DIN to VGA adapter is as good as it gets, and for the low price it does a good job displaying crisp pixels with vivid colors. But the phase thing.. yeah.

There is an interference pattern among the vertical stripes while a floppy disk is loading (which was also there with the old PSU), so if this is related to a capacitor then at this point it is one of the many inside the ST itself, thus well beyond my expertise.