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Atari ST on Amiga 1080 monitor?

SiriusHardware

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OK, the difference between the output from the Spectrum and the output from the ST is that while the R-G-B signals from the Spectrum are TTL-Level (between 0V-5V) the R-G-B signals from the ST are 'Video Level' (much less), so that would tend to explain why the output from the Spectrum is always going to look brighter on any given monitor - in fact in a lead for connecting the RGB output from a Spectrum to a video type RGB monitor, there normally needs to be some attenuation of the signals. Does the Spectrum portion of the cable have some attenuator resistors in it or is it just straight through from R, G, B out of the Spectrum to R, G, B in of the monitor (via the ST lead)? Does the Atari section of the lead have resistors in the R-G-B signals?

Another consideration is that VGA monitors normally have separate syncs which have to be fed with Vysnc and Hsync respectively, I do seem to remember that there were separate V and H syncs available from the Spectrum. There are also separate V and H syncs outputs available on the Atari but they don't have very strong drive capability so if the V and H sync inputs on the VGA monitor have a low internal resistance of 75 ohms as they often do, the V and H sync outputs from the ST are not 'strong' enough to drive those 75 ohm loads.

With the power to everything turned off, measure the resistance from the monitor VGA Vsync input to monitor GND and from the monitor VGA Hsync input to monitor GND, and if those resistances are substantially higher than 75 ohms (maybe 330 ohms or higher) you can try connecting the separate V and H syncs out from the ST to those inputs (if that is not already what you are doing) to see if that gives you a centred image.
 

SiriusHardware

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What is the brand and model of your multisync LCD monitor? NEC, by any chance, or something else?
 

Divarin

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Does the Spectrum portion of the cable have some attenuator resistors in it or is it just straight through from R, G, B out of the Spectrum to R, G, B in of the monitor (via the ST lead)? Does the Atari section of the lead have resistors in the R-G-B signals?
Yeah I added resistors in the spectrum cable. I did not add any in the ST cable.
With the power to everything turned off, measure the resistance from the monitor VGA Vsync input to monitor GND and from the monitor VGA Hsync input to monitor GND, and if those resistances are substantially higher than 75 ohms (maybe 330 ohms or higher) you can try connecting the separate V and H syncs out from the ST to those inputs (if that is not already what you are doing) to see if that gives you a centred image.
Okay that gives me something to work off of I'll do that when I get a chance tomorrow, thanks.
What is the brand and model of your multisync LCD monitor? NEC, by any chance, or something else?
Marshall Lynx hmmm M-LYNX-15-RM, I guess? I have it on a mounting bracket and it's partially covering the stickers on the back but I think that's the model number.
 

SiriusHardware

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Just looked that up, and although it is a discontinued product, I saw the price it once sold for, Woo! around 500 to 600 dollars.

Just wondering if your ST is actually a USA model - it seems likely, but then I think you imported your Spectrum from the Mediterranean area somewhere, so it's not a given. If it is a foreign model from a 50Hz country that could explain the offset as the monitor specs don't mention any frame rate lower than 60Hz.
 

g4ugm

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Sounds like your VGA monitor is not quite happy with the output from the Atari. If you are messing with a lot of kit you might want to get an EXtron converter box like this:-


manual here:-


which allows lots of adjustments to the video. I haven't tried that one myself, I have the later box which outputs HDMI....
 

Divarin

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Sounds like your VGA monitor is not quite happy with the output from the Atari. If you are messing with a lot of kit you might want to get an EXtron converter box like this:-


manual here:-


which allows lots of adjustments to the video. I haven't tried that one myself, I have the later box which outputs HDMI....
Hmm not a bad idea. Yeah I kind of have one "retro station" and frequently swap out different computers. There's two monitors, a 1702 and this Marshall Lynx. The lynx accepts both PAL & NTSC signals and has inputs for composite, component, s-video, VGA, and DVI (so also HDMI if using an HDMI to DVI adapter). Between these two monitors plus an old VHS VCR for converting RF output to composite lets me use just about anything that I have (outside of PCs and portables).

The ST is the only one that doesn't look so great.

A device like this would be a nice to have.
 

Divarin

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Sounds like your VGA monitor is not quite happy with the output from the Atari. If you are messing with a lot of kit you might want to get an EXtron converter box like this:-


manual here:-


which allows lots of adjustments to the video. I haven't tried that one myself, I have the later box which outputs HDMI....
Got this device yesterday and hooked it up this morning, wow it works great. the picture is crystal clear now. Very inexpensive solution. I might see if I can hook up some other computers to it now such as my vic-20 which is also pretty muddy looking.

Thanks for the suggestion.
 

g4ugm

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Got this device yesterday and hooked it up this morning, wow it works great. the picture is crystal clear now. Very inexpensive solution. I might see if I can hook up some other computers to it now such as my vic-20 which is also pretty muddy looking.

Thanks for the suggestion.
Glad it works. I am sure that these were not cheap when new, but are now as folks are switching to HDMI. Mind you the later devices which convert to HDMI are also appearing used at reasonable prices....
 

Divarin

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Glad it works. I am sure that these were not cheap when new, but are now as folks are switching to HDMI. Mind you the later devices which convert to HDMI are also appearing used at reasonable prices....
Yeah. Only issue is now the speccy doesn't look so great through it so I am going to have to sort of replan my whole setup here, maybe make a separate cable for the speccy to connect directly and not use the ST cable. But, it definitely works for the ST.

One other really important thing to mention and will be of use to other ST owners who are looking for display options is that the box also converts the signal to a sync frequency compatible with your run-of-the-mill vga monitor (The one I am trying it with right now is a 15" CRT that I found on the curb). I know one of the hard (and expensive) things to get an ST going is to source a multisync monitor that is compatible with the ST's sync frequency so a box like this not only cleans up the video but also lets you use a monitor that otherwise wouldn't work with it.
 
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