Help with Atari STf - RGB - Cannot get video/sync

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walterg74
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Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sun Aug 28, 2016 3:13 am

Today I decided to test (among other things), a recently acquired Atari 1040 STf NTSC I purchased from ebay. I had two other STs (a 1040 STFM and a 520 STe w/4MB) but both were PAL and I wanted to also have an NTSC machine.

The computer was listed as "pristine" and shown working with the Atari monitor, but for convenience, shipping,etc. I made an offer and purchased just the computer.

Ok background set, here is what happened.

My initial tests were with a Commodore 1084S-D2 monitor, and an Atari ST RGB-SCART cable plus a SCART/DB-9 adapter cable.

I first tested a 520 STFM, and a 520 STE. Both worked just fine, I tested a few games, ran sysinfo etc., so I know both the monitor and cables work ok.

When I went to test the 1040 STf, I did not get a picture. All I got were some rolling horizontal stripes that seemed to be made up of red, white, black, etc. (the computer itself did power up, and loaded the disk, etc. )

I decided to go a different route, and pulled out a Sony PVM (that I had to test anyway), along with a SCART-BNC cable.

Since this has more options to play around with, I managed to learn some more. Connected properly, the screen stays black, and monitor says it's not receivng sync. Playing around with the inputs for the RGB, selcting "composite" (it's not actual compiste) Imdo see the screen but in a weird red tint, then goes away.

I tested the same setup with other consoles and computers (I had a lot to test pending anyway!) and all these worked fine with the same SCART-BNC cable (and their respective RGB-CART cable): The previously tested Ataris, ZX Spectrum 128 +2, Playstation, Neo Geo CD, Saturn, Super Nintendo. Everything works fine, it is only the STf that refuses to cooperate... :)

So... Finally... WTF is wrong?

- I know the STf doesn't output composite video, but is it also missing the Composite / Composite video Sync on pin 2 and that's why I get nothing? Everything I read so far says they're all the same for sync, and the same cable should work for all models.

- If so, how does the Atari Monitor work then? Does it directly use H-sync and V-sync signals instead?

- if I wanted it then to work with the Commodore Monitor, would I have to make my own cable and use the separate H-sync and V-sync signals?

- If I want to use the PVM monitor, that only has ONE external sync input, then what? How would I have to produce such input?

Thanks!!!

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Mon Aug 29, 2016 10:33 pm

Anyone..?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Tue Aug 30, 2016 6:11 am

Yes, Atari monitors (at least SM124, SC1224) use the separate H and V sync signals. Composite sync on pin 2 is generated from these signals via a very simple circuit inside the STf: two diodes, one transistor, some resistors. Theoretically, this circuit could be damaged. I've also heard somewhere that very early STs didn't have the composite sync circuitry, but I think this only refers to very early 520STs.

Are you able to measure (e.g. with an oscilloscope) if there is a composite sync signal on pin 2?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Tue Aug 30, 2016 3:56 pm

czietz wrote:Yes, Atari monitors (at least SM124, SC1224) use the separate H and V sync signals. Composite sync on pin 2 is generated from these signals via a very simple circuit inside the STf: two diodes, one transistor, some resistors. Theoretically, this circuit could be damaged. I've also heard somewhere that very early STs didn't have the composite sync circuitry, but I think this only refers to very early 520STs.

Are you able to measure (e.g. with an oscilloscope) if there is a composite sync signal on pin 2?


Hi, thanks for replying!

Don't really have a scope, at best a multimeter. I do have some more info though. I got one of those atari to philips monitor cables. Doing a simple continuity test it would seem it has both pin 2 plus the H & V sync pins wired as well.

With this cable hooked up to the 1084s I *do* get a picture now, but it rolls vertically :(

Could it be that there is *some* signal on pin 2 and is interfering/overrigind the other sync signals? And maybe it's too snall/bad as to generate proper sunc with the scart cable, that only gets sync signal from just that pin?

What if I wanted to make my own cable to feed H+V into the Comp sync that the PVM uses?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby EstTeeEfEm » Tue Aug 30, 2016 10:42 pm

Can I point you to this topic
http://www.atari-forum.com/viewtopic.php?t=28665

I had a lot of issues with this myself... and this seems to be the best answer tbh

Add 150 ohm resistors on R,G,B signals.
DO NOT add resistors on V-sync (blanking signal).

Boucing screen solution - add 100uf / 10v (or 16v, 25v) capacitor between Vsync (blanking) and groud (pin16 + / pin18 - in scart socket).
It works every time with any STF, STFM, STE even on new LCDs/Plasmas (in most cases LG are problematic).


Do read the thread tho... its quite informative :)
Have fun -- i think? :?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Wed Aug 31, 2016 1:22 am

EstTeeEfEm wrote:Can I point you to this topic
http://www.atari-forum.com/viewtopic.php?t=28665

I had a lot of issues with this myself... and this seems to be the best answer tbh

Add 150 ohm resistors on R,G,B signals.
DO NOT add resistors on V-sync (blanking signal).

Boucing screen solution - add 100uf / 10v (or 16v, 25v) capacitor between Vsync (blanking) and groud (pin16 + / pin18 - in scart socket).
It works every time with any STF, STFM, STE even on new LCDs/Plasmas (in most cases LG are problematic).


Do read the thread tho... its quite informative :)
Have fun -- i think? :?


Thanks so much, will give it a thorough read. Only problem I see is the cables I have the connectors cannot be dissasembled, so may have to cut it (although I did just buy connectors to make my own).

One doubt though, I am not sure if the scart cable I have actually does pull the H+V syncs, maybe it just assumes it's there from pin 2 and uses only that.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby veegee » Wed Aug 31, 2016 6:30 am

I had a similar problem with my Mega, it sounds like the V Sync is not getting from the Glue to the monitor plug properly.

I'm not certain but I think you won't have the composite signal since you don't have the modulator.

Use your meter to trace the H and V sync (pins 37 & 38) from the Glue chip, it's a relatively simple circuit as you don't have the modulator - the schematics are available online.

In my case it was a tiny nick in one of the tracks - quick bridge of solder and works fine!

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Wed Aug 31, 2016 6:35 am

@veegee: You still have composite sync without modulator. No composite video, though.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby veegee » Wed Aug 31, 2016 7:50 pm

czietz wrote:@veegee: You still have composite sync without modulator. No composite video, though.


Ah yes - wasn't 100% sure I had that correct! - thanks.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Wed Aug 31, 2016 8:53 pm

@walterg74: I don't have any experience with the monitors and the cables you use, so I can just speculate. If you suspect that something could be wrong with the sync signals, you can use the multimeter (set to volts, DC) to at least measure the average voltage of the sync signals. Of course the signals change rapidly (that's why I asked if you had a scope) but depending on your multimeter you will get a good approximate of the average. For example if the average voltage is 0 V, there's clearly something wrong with that sync signal.

If your multimeter can measure frequencies up to the kHz range, you can also try that.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby EstTeeEfEm » Thu Sep 01, 2016 9:53 am

Only problem I see is the cables I have the connectors cannot be dissasembled,


Mine was similar to this... turns out, although at quick glance they couldnt be disassembled, they could be prized open.. mine were merely glued together. Bought from "Retro Computer Shack" on Ebay... If it LOOKS similar to the ones you bought, then they are probably glued... but I hold no responsibility if you break them :)

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby iggydrougge » Sun Sep 04, 2016 1:05 am

walterg74 wrote:Thanks so much, will give it a thorough read. Only problem I see is the cables I have the connectors cannot be dissasembled, so may have to cut it (although I did just buy connectors to make my own).


Every Scart connector I've ever seen can be disassembled; unscrew the end where the cable enters and pull the casing apart.

walterg74 wrote:One doubt though, I am not sure if the scart cable I have actually does pull the H+V syncs, maybe it just assumes it's there from pin 2 and uses only that.

No Scart cable ever uses H+V sync since there are no pins in the Scart standard for separate syncs.

Unlike an STFM or STE, the STF doesn't offer composite video on pin 2 of the DIN-13 connector, but only a pure composite sync signal (CSYNC). That signal is at TTL levels unlike the composite video signal your cable probably expects. TTL signals are at higher levels than composite video, which should be brought down to a video level by using a higher value resistor on that line. Ian Stedman recommends 330 ohms.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 4:35 pm

Hey guys, thanks for your replies! Sorry but have been away. Will answer now

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 5:01 pm

EstTeeEfEm wrote:Can I point you to this topic
http://www.atari-forum.com/viewtopic.php?t=28665

I had a lot of issues with this myself... and this seems to be the best answer tbh

Add 150 ohm resistors on R,G,B signals.
DO NOT add resistors on V-sync (blanking signal).

Boucing screen solution - add 100uf / 10v (or 16v, 25v) capacitor between Vsync (blanking) and groud (pin16 + / pin18 - in scart socket).
It works every time with any STF, STFM, STE even on new LCDs/Plasmas (in most cases LG are problematic).


Do read the thread tho... its quite informative :)
Have fun -- i think? :?


I actually had read that, so I think it-s a matter of first looking at what exactly is in my cables...

I have 2. One is an Atari 13 pin DIN to SCART cable. From what I talked with they guy that makes them I assume this just connects pin 2 from the Atari to the appropriate pin for sync on the SCART connector. The other is a 13 pin DIN to a DB-9 connector, that fits on the Atari SC-1435 type and 1084S type monitors.

So far the results were:

With the SCART cable and SCART to DB-9 adapter: no proper image on the 1084S-D2, just diagonal colored bars. Same cable but with a SCART to BNC adapter cable into a PVM monitor: says no sync signal (but if you switch inputs back and forth I see the image in the background in a purplish tone

With the direct DB-9 cable, image appears but rolls vertically. This cable seems to connect ALL signals (both pin 2 and the separate H + V sync pins)

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 5:07 pm

czietz wrote:@veegee: You still have composite sync without modulator. No composite video, though.



Are you 100% sure? The guy I bought the cable from (from retro computer shack) said that there is NOTHING on pin 2 on this model, hence why the cable would not work... :shrug:

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 5:08 pm

czietz wrote:@walterg74: I don't have any experience with the monitors and the cables you use, so I can just speculate. If you suspect that something could be wrong with the sync signals, you can use the multimeter (set to volts, DC) to at least measure the average voltage of the sync signals. Of course the signals change rapidly (that's why I asked if you had a scope) but depending on your multimeter you will get a good approximate of the average. For example if the average voltage is 0 V, there's clearly something wrong with that sync signal.

If your multimeter can measure frequencies up to the kHz range, you can also try that.


Thanks I will give it a try and see what happens/what I read

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 5:09 pm

EstTeeEfEm wrote:
Only problem I see is the cables I have the connectors cannot be dissasembled,


Mine was similar to this... turns out, although at quick glance they couldnt be disassembled, they could be prized open.. mine were merely glued together. Bought from "Retro Computer Shack" on Ebay... If it LOOKS similar to the ones you bought, then they are probably glued... but I hold no responsibility if you break them :)



That's the same place my SCART cable is from. Not really sure because the guy that makes them told me it would not work with the STF because there is nothing on pin 2 on it...

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 5:12 pm

iggydrougge wrote:
walterg74 wrote:Thanks so much, will give it a thorough read. Only problem I see is the cables I have the connectors cannot be dissasembled, so may have to cut it (although I did just buy connectors to make my own).


Every Scart connector I've ever seen can be disassembled; unscrew the end where the cable enters and pull the casing apart.

walterg74 wrote:One doubt though, I am not sure if the scart cable I have actually does pull the H+V syncs, maybe it just assumes it's there from pin 2 and uses only that.

No Scart cable ever uses H+V sync since there are no pins in the Scart standard for separate syncs.

Unlike an STFM or STE, the STF doesn't offer composite video on pin 2 of the DIN-13 connector, but only a pure composite sync signal (CSYNC). That signal is at TTL levels unlike the composite video signal your cable probably expects. TTL signals are at higher levels than composite video, which should be brought down to a video level by using a higher value resistor on that line. Ian Stedman recommends 330 ohms.


Ok so this is the confusing part, as some people say there is sync and others that there is nothing.. I guess then to see if this is the case I could try adding the resistor to the cable and see what happens...

Now on the other hand, the db-9 cable I have DOES have the H + V signals.. but with that one the picture rolls... so what would that be about?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Sat Sep 10, 2016 5:37 pm

walterg74 wrote:
czietz wrote:@veegee: You still have composite sync without modulator. No composite video, though.

Are you 100% sure? The guy I bought the cable from (from retro computer shack) said that there is NOTHING on pin 2 on this model, hence why the cable would not work... :shrug:


Yes, I am 100% sure. For my 1040STf at least, because I have measured pin 2 with a scope and found a TTL level composite sync. BTW: I have a SCART cable wired this way ...
Image
... that wouldn't work, if there was nothing on pin 2.

walterg74 wrote:Now on the other hand, the db-9 cable I have DOES have the H + V signals.. but with that one the picture rolls... so what would that be about?


One of the sync signals is maybe missing? Did you get around to measure the (average) DC voltage level at the corresponding pins?

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 7:19 pm

czietz wrote:
walterg74 wrote:
czietz wrote:@veegee: You still have composite sync without modulator. No composite video, though.

Are you 100% sure? The guy I bought the cable from (from retro computer shack) said that there is NOTHING on pin 2 on this model, hence why the cable would not work... :shrug:


Yes, I am 100% sure. For my 1040STf at least, because I have measured pin 2 with a scope and found a TTL level composite sync. BTW: I have a SCART cable wired this way ...
Image
... that wouldn't work, if there was nothing on pin 2.

walterg74 wrote:Now on the other hand, the db-9 cable I have DOES have the H + V signals.. but with that one the picture rolls... so what would that be about?


One of the sync signals is maybe missing? Did you get around to measure the (average) DC voltage level at the corresponding pins?



Ok, so measuring pin 2 and 13 on the Atari, I seem to get when setting the multi-meter to V, a measure that fluctuates roughly between - 0.05 (or maybe -0.08) and +0.05 (or +0.08)... If setting to frequency, the reading shows up at something like 0.03?

Regarding the second part, not sure, I will measure the H & V pins now and see what comes up.

Regarding your diagram, is that-s how you have it wired, aren-t you also feeding pin 2 straight? (and therefore the TTL level you mention?)

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Sat Sep 10, 2016 7:52 pm

walterg74 wrote:Ok, so measuring pin 2 and 13 on the Atari, I seem to get when setting the multi-meter to V, a measure that fluctuates roughly between - 0.05 (or maybe -0.08) and +0.05 (or +0.08)... If setting to frequency, the reading shows up at something like 0.03?


Pin 2 is at ground potential (0 V) more or less, so indeed there seems to be no signal coming out of pin 2. I see around 3 V average DC voltage on my 1040STf at pin 2. The exact value will depend on the multimeter and vary from computer to computer, but it won't be that close to 0 V. This still doesn't explain why your monitor with separate H and V sync doesn't work, either ... unless one of those signals is also dead.

walterg74 wrote:Regarding your diagram, is that-s how you have it wired, aren-t you also feeding pin 2 straight? (and therefore the TTL level you mention?)


Yes, I'm feeding pin 2 (composite sync) directly into pin 20 of the SCART connector. Because of the TTL levels this "overdrives" the input, but none of the several TVs I used this cable with had any issues with that.
Last edited by czietz on Sat Sep 10, 2016 7:53 pm, edited 1 time in total.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 8:01 pm

czietz wrote:
walterg74 wrote:Ok, so measuring pin 2 and 13 on the Atari, I seem to get when setting the multi-meter to V, a measure that fluctuates roughly between - 0.05 (or maybe -0.08) and +0.05 (or +0.08)... If setting to frequency, the reading shows up at something like 0.03?


Pin 2 is at ground potential (0 V) more or less, so indeed there seems to be no signal coming out of pin 2. I see around 3 V average DC voltage on my 1040STf at pin 2. The exact value will depend on the multimeter and vary from computer to computer, but it won't be that close to 0 V. This still doesn't explain why your monitor with separate H and V sync doesn't work, either ... unless one of those signals is also dead.

walterg74 wrote:Regarding your diagram, is that-s how you have it wired, aren-t you also feeding pin 2 straight? (and therefore the TTL level you mention?)


Yes, I'm feeding pin 2 (composite sync) directly into pin 20 of the SCART connector. Because of the TTL levels this "overdrives" the input, but none of the several TVs I used this cable with had any issues with that.



The V & H pins were measuring something like +- 0.19. Is that better?

But... I gotta buy a vowel...

So it turns out I have TWO cables that are of the 13-pin to DB-9 pin type, as I had another one come with an Atari SC-1435 monitor that doesn't work currently...

I decided to measue again but with the cable hooked up to the Atari, and measure on the DB-9 side.

I measured on the cable I was using until now, and when I measure between GND and V-Sync, the meter showed a fixed 1 ( not 1.00, that means it's shorted right?). So I though "ok, it's this cable that has a problem". So I tried the other cable and it was measuring fine on both pins (also a side note, that cable did not even have a pin 7 and was working fine on the 1435 with just h + v sync). So I said "A-ha, it was the cable and this one should work". But lo and behold, no.. I hooked it up with this cable and same problem! The image is there but just rolls vertically... :?:

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 8:12 pm

Also, are you sure about the voltage? Schematics page says:

Atari ST Video Signals Characteristics
The Characteristics of the Video Signals used by the Atari are the following:
Output Level 1 Volt Peak to Peak (P-P) for Video (R.G.B.) and Synchronization lines

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby czietz » Sat Sep 10, 2016 9:26 pm

And again: yes, I am 100% sure. As already mentioned, I do own a scope and I measured those signals. At a high impedance input (such as a multimeter or a scope) these signals are definitely much higher than 1 Vpp. And even if they weren't, the DC level still would not be at 0 - 0.2 V.

I'd say the sync signals are missing, assuming you measured correctly. But since you keep questioning me, anyway, I suggest you find someone else -- possibly in your vicinity and with an oscilloscope -- to aid you with the troubleshooting.

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Re: Help with Atari STf - RGB - Cannot get video/sync

Postby walterg74 » Sat Sep 10, 2016 10:43 pm

czietz wrote:And again: yes, I am 100% sure. As already mentioned, I do own a scope and I measured those signals. At a high impedance input (such as a multimeter or a scope) these signals are definitely much higher than 1 Vpp. And even if they weren't, the DC level still would not be at 0 - 0.2 V.

I'd say the sync signals are missing, assuming you measured correctly. But since you keep questioning me, anyway, I suggest you find someone else -- possibly in your vicinity and with an oscilloscope -- to aid you with the troubleshooting.


Nope, not questioning (and don't get mad, first time was about if there was signal at all, now it was about the level of that signal :P), but sometimes there are typos, so asking just in case...

I don't know, I think it may be a combination of things, with the Atari and this particular monitor.

I just tried one of my other ataris with the same cable, and while I *do* get a good picture of the desktop initially, if for example I select "about" the desktop, when the info screen pops up it starts rolling....

In summary then would you say this is correct?:

- My STF should have Sync on pin 2 anyway, but I would need to add a 330 ohm resistor on the cable to pin 20 of the SCART to bring it to acceptable level (although in your case you didn't need it) and that should work when connecting to my PVM.

- Another option could be to modify and make my own cable where I combine the H-Sync + V-Sync signals (with a couple of resistors I saw here: http://atariage.com/forums/topic/91644- ... try1583158 ) and feed that result to pin 20 of the scart connector.

Does that sound about right?


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