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Atari ST on Amiga 1080 monitor?

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Divarin

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Mar 9, 2019
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Cleveland, OH
Hi! I picked up an Amiga 1080 (not 1084) monitor, seems to work fine with a composite input.
I'm trying to see if I can connect an 1040 ST to it. I have a 13 pin din cable and toned out each of the wires so I know which colored wire goes to which pin.
I found some pin-outs of the 1080 such as the one on this page. I have the monitor set to analog RGB but am unable to get a picture.
Here's what I have so far:
Signal13 pin din (ST)9 pin (Amiga 1080)
Ground131
Red73
Green64
Blue105
Composite sync28
V. Sync129
 
Why are you using composite sync? Shouldn't h-sync (1080 pin 8) come from Atari pin -9. D
Or feed composite sync to 1080 pin 7?
is it overloading the 1080? I think the ST produces 5v video, usual to insert 150ohm resistors
 
I did try just using composite sync originally, from pin 2 to pin 7 but didn't get anything
I didn't notice (until just now) that h.sync was available coming out of the ST on pin 9, I don't know if I was just looking at an incomplete pinout or what.
Anyway so I tried v.sync and h.sync instead of composite sync:
h.sync from pin 9 to pin 8
v.sync from pin 12 to pin 9
Also added 150 ohm resistors for the R, G, and B signals.
Still nothing.
 
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I made a cable for my Atari ST to my 1084. I used composite sync because I also wanted the cable to work with my PVM’s. Strange that you aren’t getting anything to it it should work.

Does your st have an rf modulator? If it doesn’t you need to build a little circuit to get composite video out to the din (and thus composite sync). Also assuming the 1080 is in good order as well? Those are pretty good monitors I have one as well used it for my amigas and as a cga monitor before I got a Tandy branded one. If you haven’t done so I would test out analog rgb input with another computer as well.
 
mbliss11 said:
I made a cable for my Atari ST to my 1084. I used composite sync because I also wanted the cable to work with my PVM’s. Strange that you aren’t getting anything to it it should work.

Does your st have an rf modulator? If it doesn’t you need to build a little circuit to get composite video out to the din (and thus composite sync). Also assuming the 1080 is in good order as well? Those are pretty good monitors I have one as well used it for my amigas and as a cga monitor before I got a Tandy branded one. If you haven’t done so I would test out analog rgb input with another computer as well.
Click to expand...
From what I have read you don't need the RF modulator for composite sync, its there all the time. This makes sense as its just a passive combination of H and V Sync and has nothing to do with composite video, which will always have its own sync. I can't check as my current Atari is an STE so has a modulator. You probably used it as lots of circuits do because they are going to SCART and that needs a trigger to set it to RGB mode.

Do you have any other way to check what is at fault?
 
No my ST does not have an RF modulator.

The ST itself it working fine I already have another cable I built a long time ago which adapts it to VGA (using a monitor that supports the sync frequency) and that works.
I picked up this monitor for a friend of mine as I picked him up another ST at VCFMW last year. I tested out that ST before giving it to him using my cable/monitor setup, but so far he has been unable to find another monitor that would work for him.
So now I'm trying to build an ST to 1080 cable, ensure this monitor works with the ST (the monitor itself works using composite input at least)

One thing if someone can double check my thinking here.
When it comes to pinouts. generally they are numbered from top to bottom, left to right if you're looking at the solder side of the cable, is that right?
so in a diagram like this:

.1....2....3....4
.5....6....7....8
.9..10..11..12
.........13

that's from the solder side of the din connector. Since I was toning-out the pins from the other side (the pins that actually go into the socket on the ST) I numbered then like this:

..4....3....2....1
..8....7....6....5
12..11..10....9
.........13

But, maybe I have that backwards?
 
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g4ugm said:
From what I have read you don't need the RF modulator for composite sync, its there all the time. This makes sense as its just a passive combination of H and V Sync and has nothing to do with composite video, which will always have its own sync. I can't check as my current Atari is an STE so has a modulator. You probably used it as lots of circuits do because they are going to SCART and that needs a trigger to set it to RGB mode.

Do you have any other way to check what is at fault?
Click to expand...
forums.atariage.com

Found a working SCART->HDMI adapter on Amazon

I have been on the look-out for an alternative to the expensive Framemeister and I am happy to say I found something! Here is a link to the adapter : https://www.amazon.com/dp/B01N06Q9WH/ref=cm_sw_em_r_mt_dp_U_cWSOCb1TRTAMN& In case the link expires some time in the future just search for thi...
forums.atariage.com forums.atariage.com

Used this on my early 520 ST to get composite sync out. Mine is an NTSC US version seems to be isolated to US models.
 
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Divarin said:
No my ST does not have an RF modulator.

The ST itself it working fine I already have another cable I built a long time ago which adapts it to VGA (using a monitor that supports the sync frequency) and that works.
I picked up this monitor for a friend of mine as I picked him up another ST at VCFMW last year. I tested out that ST before giving it to him using my cable/monitor setup, but so far he has been unable to find another monitor that would work for him.
So now I'm trying to build an ST to 1080 cable, ensure this monitor works with the ST (the monitor itself works using composite input at least)

One thing if someone can double check my thinking here.
When it comes to pinouts. generally they are numbered from top to bottom, left to right if you're looking at the solder side of the cable, is that right?
so in a diagram like this:

.1....2....3....4
.5....6....7....8
.9..10..11..12
.........13

that's from the solder side of the din connector. Since I was toning-out the pins from the other side (the pins that actually go into the socket on the ST) I numbered then like this:

..4....3....2....1
..8....7....6....5
12..11..10....9
.........13
Click to expand...

If you don’t have a modulator you will not have composite video or sync and will need to make the circuit in the link I posted above should you want composite video and composite sync. I am assuming since you went to VCF Midwest that you are in the states and that you have an NTSC ST.

Your pinouts may be backwards check this link has good diagram and marked pin out:


Couple posts down view from solder side diagram is to a scart cable. I think I used this when making my cable but I did to vga cable all of my cables with my machines use vga connector for simplicity and ease of use with PVM’s
 
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mbliss11 said:
If you don’t have a modulator you will not have composite video or sync and will need to make the circuit in the link I posted above should you want composite video and composite sync. I am assuming since you went to VCF Midwest that you are in the states and that you have an NTSC ST.
Click to expand...
sorry I think there's some confusion, I don't want composite video. I want to use the analog RGB input on the 1080 monitor. I was just saying that I have used the composite input on the monitor just to verify that the monitor (appears to be) working, in general, although it's possible there's something wrong with the analog rgb input. I doubt it though, most likely I'm just not wiring things up correctly.

I was using composite sync in place of H.Sync because I made a mistake reading the pinout (or the page I was looking at didn't show the h.sync signal, I don't know which as I didn't bookmark the page) But now I am trying to use the H.Sync and V.Sync along with the ground and R, G, B and am ignoring the Composite sync pin on the ST.
 
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mbliss11 said:
Your pinouts may be backwards check this link has good diagram and marked pin out:


Couple posts down view from solder side diagram is to a scart cable. I think I used this when making my cable but I did to vga cable all of my cables with my machines use vga connector for simplicity and ease of use with PVM’s
Click to expand...
Yeah I see what you mean. I'll try re-wiring it with the assumption that I've numbered my pins backwards. I did try that once but that was while I was still trying to use the composite sync and before adding the resistors.
 
Composite sync is carried by the composite signal so you wouldn’t have it without composite video. Just want to share that was probably the reason it didn’t work when you tried…that or your pinout was backwards ;)

Hope the 1080 works though those are solid monitors. I have one and a 1084s I like the non glossy finish on the 1080 more but the 1084 does pal ntsc switching automatically whereas on the 1080 you need to find the sweet spot on vhold so that it works for both signals
 
okay swapped the wires around but still nothing. I tried both with and without the resistors on the R, G, and B lines.
I don't even see a flash or anything on the monitor to indicate that any sort of signal is there. but I'm not sure what to expect.

Without the resistors, if I switch it to digital RGB I can see the ST's desktop but it's rolling, dark, and blue. I wouldn't really expect that to work any better than that since it's an analog RGB signal but ... just as a test.
 
Where there is no modulator fitted there is often a composite sync circuit, or at least the holes to put the components for one in, where the modulator would have been. It's a transistor and a handful of other components, very easy to add if it is not already present on the PCB.
 
To enlarge on the above, here is a diagram section showing both the circuitry which is present when there is a modulator, and the csync circuitry which is sometimes present when there isn't a modulator. The csync output circuit is centred on Q12 in the green oval and would only be present when there is no modulator fitted - very often the PCB tracks and holes to support this circuit are within the outline of the missing modulator.

If your PCB has the tracks and component holes / positions for the csync circuit already present, great, just populate the empty holes with the correct components. When this circuit is present you get csync out on what would normally be the composite-video output pin of the monitor socket.

If there is no provision on the PCB for the csync circuit then just build it yourself: One transistor, three resistors, two diodes. Be careful with the pinout of the 2N3904 - as you have noted in the past the first 2N3904 pinout you find online isn't always the correct one.

STF_MonitorOutput.png
 
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DD6C01F2-981D-4354-ABFE-FB93B7457A42.jpeg
Mine looked like this on early 520 st model this was posted on Atari forum as well. Very easy mod to do
 
Thanks but I'm not really interested in trying to get a composite signal.

My ST (as well as the one my friend has which this monitor will be for, eventually, if I can get it to work) do not have composite outputs as they do not have RF modulators. Even if they did I would still want to use the RGB outputs and that's what I'm attempting to get working right now. The only reason composite was mentioned earlier is a) I tested that the monitor isn't dead using a composite source and b) in one of my earlier attempts I was using the composite sync wire (which I now know doesn't have anything on it) instead of what I should have been using (H.Sync).

Both STs are outputing valid RGB, H.Sync and V.Sync signals. I can verify this by connecting them to a VGA monitor (which supports the sync frequency of the ST) using an ST to VGA cable I built some time ago (a little more than a year now I think).
 
Hmm you don’t happen to have a hard drive hooked up to your st or a config disk in it do you? Could the monitor preference for high res have been saved since it’s last boot? I have never used a high res monitor with mine and from what I understand I think there is an additional his res signal that needs to be present too that detects that. Would suggest booting with no media present on the st if it does. I’m just throwing ideas at the wall now.

Unknowns are if analog rgb signal is operating correctly on the st, pinout for cable is correct or if the monitor is working and can receive analog rgb signal correctly.
 
mbliss11 said:
Hmm you don’t happen to have a hard drive hooked up to your st or a config disk in it do you? Could the monitor preference for high res have been saved since it’s last boot? I have never used a high res monitor with mine and from what I understand I think there is an additional his res signal that needs to be present too that detects that. Would suggest booting with no media present on the st if it does. I’m just throwing ideas at the wall now.

Unknowns are if analog rgb signal is operating correctly on the st, pinout for cable is correct or if the monitor is working and can receive analog rgb signal correctly.
Click to expand...
No, no hard drive.
I know the RGB signal on the ST is operating correctly, just to double check I re-connected it to my VGA monitor using that ST to VGA cable I mentioned. It's working as expected.
I guess the most likely thing left is that the monitor doesn't work in analog RGB mode. Or possibly that the monitor just doesn't support the signal the ST is giving it, wrong sync frequency maybe? I don't know. I've read some posts on Atari Age about people using ST's on 1084's but I don't know about the 1080.
I do have an Amiga 500 I can try building a cable for just to prove to myself that the monitor does work in analog RGB mode. Currently I have an RGB2HDMI mod installed in it but that shouldn't stop me from using the 23 pin jack on the back as well.
 
This might be a clue, if I can trust it:
https://old.pinouts.ru/Video/C1084dd_pinout.shtml

PinNameAnalog ModeDigital Mode
1GNDGroundGround
2GNDGroundGround
3RRedRed
4GGreenGreen
5BBlueBlue
6In/cIntensity
7CSYNSComposite Syncn/c
8HSYNCn/cHorizontal Sync
9VSYNCn/cVertical Sync

This is for a 1084d or 1084dS so I don't know if it applies to the 1080 but if it does it would mean that the separate h.sync and v.sync signals are ignored while in analog mode and it does require a composite sync.
 
The 1080 should work. Even if vhold was out of wack on it you would at least see a rolling picture of some kind.

I’d try another source just to rule out issues with the monitor. If you get a picture with your amiga then you’ll at least know it’s your cable that’s the culprit
 
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