Atari ST 520 video cable to Scart

    Good evening to all Atari fans.

    First of all, I want to apologize for the English language, I don't know German well enough to write here :)


    Recently I got Atari 520 ST system, but it quickly understood that no games work on a regular monochrome monitor :(


    Therefore, I decided to make a cord to connect to the TV via Scart connector.

    A few days ago I received a 13 din plug and started assembling the cable.

    But I didn't succeed. I've looked through 5 schematics from different sites, English and French, but my German Atari doesn't show anything! ((((

    I tried these everything on 2 TFT TVs and on one CRT, but i hadn't success. I tried many different pinouts combinations, different resistors, diodes, capacitors. But it didn't help.

    Later I realized that there is no voltage of 12 volts on my Atari, on the video connector! What is needed to Scart. I had the 8th video pin connected to GND in my Atari. I disconnected it from GND and applied 12 volts from the power connector. And again I redid all the combinations of the cord, but i had anything on the screen (((

    It's just some kind of horror.

    Does anyone know the working cable schemantic for this Atari ST 520?

    I have a motherboard revision B. (ST 520+) Like this:

    File:ST Motherboard C070243 Rev C Factor6.jpg - AtariForumWiki

    I understand that there is no composite signal?

    Do not offer the option of buying a new cable on the Internet. I won't be able to do it now, and as far as I've heard, they often don't work either. And I'm not surprised (((


    Please help, who can, who knows the scheme?
    I've been trying to make a cable for 3 evening (((

    Did You switch the SCART Connector active on the Monitor / TV-Set ? Probably your device doesn't do this automatically. AV1 should be the channel of choice.

    Otherwise I can't imagine, that You can't get an image with 3 different cables.



    Thats the variant I would choose, if I had to solder such a cable

    CHZ-Soft - Diverse Kleinigkeiten für den Atari ST

    -- 1982 gab es keinen Raspberry Pi , aber Pi und Raspberries

    Yes, of course, I switch the TV to the Scart input.

    According to this scheme, I assembled the cord, the only nuance is that I did not take exactly the same diode, but the first one that I found in spare parts. It looks the same, glassy and small. I think it is not fundamental? when a diode passes current only in one direction?

    The diode is not really necessary to get a picture, the original cables from Atari were without any elctronic components inside, just the cable.


    You asked for compositive video signal: Only those STs which have a HF/RF modulator also have composite video. The STs without HF/RF modulator output composite sync on pin 2.


    The solution of your problem might not be to modify the cable. The problem might be the monitor/tv set you are using. This is because there is different "level" of SCART connector over there. ST neends obviously RGB+H+V-Sync version of SCART. But there is also RGB+Composite-Sync (here you would see picture but out of sync). And there is also SCART only understanding Composite video and SCART only understanding S-Video signal (luminance+chrominance). This depends on your monitor/TV-set, some are able to switch between these modes (auto or manual), some not. Some TV-sets used to have different scart connector supporting the different variants of SCART. Some TV sets could be forced to RGB+H+V by feeding SCART ping 8 with 12V, so connecting the 12V output pin 8 of the ST monitor port to SCART ping 8 is essential for such TV-sets.


    Atari ST Interfaces / Connectors / Cables Information

    1ST1

    Yes, i know this all, so I tested it all on three TVs.

    I even connected my Soviet Spectrum computer to them, about which they directly write that it is not fully compatible with the scart connector and not all TVs can output images from it. But it works fine on these TVs. So I guess Atari would may too?


    I think the problem is that all cords offer to take a composite signal from pin number 2. But in the information on the link from here: https://info-coach.fr/atari/hardware/interfaces.php (Atari Video Connector)

    it directly says that a computer like mine does not have a composite signal on the second pin.

    And yes, I saw it judging by the Atari schemantic, I have this second contact not connected anywhere at all!



    It was the same with the 8th pin of the Atari video, judging by the diagram it was connected to the ground. I turned it off and applied 12 volts to it, so that the scart of the TV understood that it was necessary to switch

    But anyway, I think i don't have the sync!

    I just don't understand why all these schemes, for example from the first link:https://www.chzsoft.de/site/ha…ri-st-nach-scart-farbmodi

    Why do all these circuits take only one VSYNC sync from the 12th pin. And where is HSYNC from the 9th pin of the atari? Maybe I need to do something about it?

    Zitat

    So which kind of signal is your russian computer using? RGB+H+V-Sync?

    Yes, it using one Sync signal but it is not fully compatible with PAL standard, so maybe you will have a problems when your TV doesn't understand this signal correctly.


    Zitat


    does your ST has HF/RF-modulator

    No, as I understand it doesn't have :(

    As i think, i need to make one sync signal from Vsync and Hsync from Atari, but how? (((

    Composite sync is already on pin 2 of ST without HF/RF modulator. Just study the circuit diagram and have a look on the board at the empty connector of the not installed rf modulator. There are one transistor plus some resistors and diode which just mix composite sync.

    1ST1

    The problem is that I have 0 volts on pin 2.
    So I understand there is no any signal ((( When i have 5 and 4 volts on pins 12 and 9

    I think I need to make one signal from of two synchronizations (H+V sync)

    it looks like you have to fix that little circuit on the mainboard.


    But anyhow, even without the composite sync you should see the (unsynced) color signal on your TV scrolling up/down. If not, you may have connected pin 4 to ground?

    1ST1

    Zitat von 1ST1

    it looks like you have to fix that little circuit on the mainboard.


    But anyhow, even without the composite sync you should see the (unsynced) color signal on your TV scrolling up/down. If not, you may have connected pin 4 to ground?

    I thought pin 4 should be open to get color video (as i want).
    It should be connected to ground when the video is monohomic

    From here:
    https://info-coach.fr/atari/hardware/interfaces.php

    Zitat

    Monochrome detection (ST/STE):

    This pin is connected to pin 17 of the MFP68901 circuit and is used to set the Atari in Hi-resolution when grounded and to Med/Low-resolution when left open. A transition on this pin generates a reset of the system. On a STE pin 3 must be left open for the detection to work.

    External Video Clock (STE):

    When pin 3 is grounded this input is used to provide an external video clock to the shifter. This allows synchronizing the video-timings with an external device so that a video Genlock device can be used without having to make any modifications to the Atari hardware.

    As I understand it, I don't have anything to solder on the board at all. Because there is simply no place for missing details.

    I only need to form the synchronization signal from the another two.

    In the topic above there is a description of how to do it. Connect the two signals together through resistors and diodes. Although it is not said which side the diodes should be ((((

    I will try different options


    The photo of my mainboard:


    This is what I told. There is nothing. Wether there is a HF/RF modulator or at these pins there is one transistor plus diodes plus resistors to mix composite video. That installation usually looks a little be like adventure as it is installed just there without a pcb.


    You already pasted the pinout of the monitor conector from the schematics, so you were already so close to the solution:



    This is the circuit to mix H and V sync to C sync. Very simple, and if one day you need to have a circuit to get "sync on green" for a workstation monitor, this is the way to go, just mix also green with it.



    See https://www.nightfallcrew.com/…st-520-low-serial-number/


    pasted-from-clipboard.png


    This is then how it should be when there is no modulator.

    Beitrag
    RE: Atari ST 520 video cable to Scart


    This is what I told. There is nothing. Wether there is a HF/RF modulator or at these pins there is one transistor plus diodes plus resistors to mix composite video. That installation usually looks a little be like adventure as it is installed just there without a pcb.

    You already pasted the pinout of the monitor conector from the schematics, so you were already so close to the solution:



    This is the circuit to mix H and V sync to C sync. Very simple, and if one day you need to have a circuit to…
    1ST1



    yalsi bitte mal umkopieren von da nach hier

    -- 1982 gab es keinen Raspberry Pi , aber Pi und Raspberries

    1ST1 Thanks again for your help. Today everything worked!


    Oddly enough, I found all the necessary spare parts on one board from an old TV tuner :)

    I also had to disconnect 12 volts from the 8th pin. With it, the TV does not show image, but when there is 0 it works.

    Also, sometimes the image moved slowly vertically. Therefore, I assembled the cord according to this scheme and when I added a 330 ohm resistor to the line from 2 to the 20th pin, then everything became fine and the image shift stopped.


    Great! (But ATARI's own handmade installation looks nicer - but as long it works...)


    I have never before seen an ST board where these points are totally unused.


    I think, probably a previous owner has removed the RF modulator without knowing that then he needs to add this little circuit. Does that 520St case has a hole behind the RF modulator? That would be a sign for a removed RF modulators, because "real RF mod less" ST have not a hole there for the RF antenna cable connector.


    And the picture really looks very sharp!

    1ST1

    I don't think that someone intervened there and took something out. Everything looks like from the factory.

    Inside the computer is a metal screen, there is a hole for the module

    But it was well sealed with copper foil.

    I think it's factory maded.

    Such things, like in this computer, do not happen often, but they still happen, I'm not the first :)

    My computer was manufactured on August 1985. Is the serial number small? 1001433 (1433 ?) I have TOS version 1.0, thank's it's built inside. Because as I read, it could be separate on a diskette an early computers :)


    This is really a low serial number. But it has been opened already as it has TOS 1.00. Those early 260/520 ST used to have BOOT-ROM first, like Amiga 1000 they requested for a TOS boot diskette before you can do anything with it. (Amiga 1000 first needs to boot Kickstart diskette, then workbench diskette). And it has already been enhanced to 1 MB by adding a 2nd layer of 16 pcs of 41256 RAMs, this also was done by ATARI with the 520ST+, but there it looks a bit different regarding the wires.


    If you ever consider having a harddisk for it, then I recommend changing to TOS 1.04, 1.00 is quite buggy with harddisk.



    This is how it would look like when it still would be in original condition. And it would only have 512 kB.

    Yes, I have plans to replace the TOS, but it is not fast, because here I have nothing. For this i need a programmer, memory chips and an ultraviolet lamp to erase them.

    First I want to buy and adapt the gotek here, but that will be another story. I hope with fewer steps than in this case))))