STs without +12V in the monitor connector

[Kairos]

There seems to be some Atari STs that lack +12V in the monitor connector.
Without modifying the computer itself what options are there for fixing this?

I'm trying to help someone who lives in the other end of the country, so it would be good if the solution kept to something like a custom SCART cable. Also this person knows nothing about these things so asking him to connect wires to capacitors etc isn't an option.

One idea is to attach an external battery and feed pin 8 of the SCART with it. But 12V batteries? Too bulky.
Is there some elegant way of transforming up an ordinart watch battery, 3V, up to 12V? Or maybe two of them, 6V to 12V?

[charles]

If some have 12v and others dont
Isnt the posdibilty still applicable to hardwire the open pin to the 12v source?

[fmen]

Can the TV be switched manually to the SCART input ? (via the remote or the front panel)
The 12V on pin 8 of the SCART does nothing more than to tell the TV to switch to its SCART input.

[frank.lukas]

If some have 12v and others dont

All Atari ST/STE Computer have over a 1k resistor +12V on pin8 at the Video connector.

[mpattonm]

If some have 12v and others dont

All Atari ST/STE Computer have over a 1k resistor +12V on pin8 at the Video connector.

Not all of them. At least early models (520ST) have pin 8 connected to ground.

Výstřižek.PNG

[Kairos]

I had previously sent the guy in question a cable where pin 8 on the 1040Atari STF, that should either be providing +12V or be tied to ground, went to pin 8 on the SCART. Resulting in a black screen. According to him, no remote control shifting brought a picture to the screen. His 1040STE though shows a picture on the same teve.

This cable has worked on the televisions I have at home, a cheap Andersson A4022FD and an antiquated Dell 17". Both with my 1040STE and with my 1040STF, which btw has no CS on pin 2.

I gave up on this and way later saw somewhere that some STs were lacking +12V on pin 8, which I imagined might be a reason for the cable not working.

[fmen]

Maybe it’s not pin 8 the problem, but pin 16: the ST SCART cable sends a vsync signal on pin 16 of the SCART plug, and while it worked on 80’s TVs, it confuses modern TVs, that expects a solid 5V on this pin. There’s a lengthy exploration, in french, of this problem here: http://fr.meric.free.fr/Articles/articl ... vplat.html

[Kairos]

Maybe it’s not pin 8 the problem, but pin 16: the ST SCART cable sends a vsync signal on pin 16 of the SCART plug, and while it worked on 80’s TVs, it confuses modern TVs, that expects a solid 5V on this pin. There’s a lengthy exploration, in french, of this problem here: http://fr.meric.free.fr/Articles/articl ... vplat.html

There is an even better explanation on this forum, by czietz:
https://www.atari-forum.com/viewtopic.php?f=15&t=37199

I actually built the cable according to his schematic, except I replaced the direct CS signal from the Atari with a HS + VS = CS solution involving a transistor and some resistors. Something like this:
https://www.retrorgb.com/building-a-pas ... biner.html

That cable works with everything I throw at it. Except for the setup the other guy has.

When I learned that some Ataris may lack the +12V pullup line, I suspected that this could be the problem. The other guy maybe didn't know how to switch input sources on his TV with the remote?

[Kairos]

Some STs indeed lack the +12V signal om pin 8 of the DIN 13 connector. Instead that pin is tied to GND.

When using a ”normal” cable, which connects pin 8 of the DIN13 connector to pin 8 of the SCART connector, the GND signal will turn off the SCART port. You’ll get a black screen. Trying to change the source with the remote will not work.

Resolution: Do not connect anything to pin 8 of the SCART. Choose input source with the remote instead. Some teves will somehow

[Kairos]

(My post was for some reason cut off, this continues it...)

Resolution: Do not connect anything to pin 8 on the SCART side. Choose the SCART port as the teve's input source with the remote instead. Some teves appear to "feel" that there's a SCART device present even without the +12V signal. Or maybe the teve's previous SOURCE setting is remembered? I'm not sure.

This cable, which lacks the +12V connection, will also work on other ST/E machines. You just need to choose the teve's signal SOURCE with the remote.

Alternatively, you can connect the +12V signal from the DIN13 connector to a switch. Let one position on the switch be feeding pin 8 on the SCART with nothing, the other with +12V. That way your SCART cable will likely suite even the oldest STs, without forsaking the newer ones.

[Zippy]

One idea is to attach an external battery and feed pin 8 of the SCART with it. But 12V batteries? Too bulky.

There are some small 12v batteries used in car alarm fobs, sizes A23 (8x28mm) and A27 (10x28mm).

Might just about be able to squeeze one inside a SCART plug or could maybe glue a battery holder to the outside of the SCART plug.

[Kairos]

Good find!
I have been looking at other types of small batteries and ways to transform them up to 12V.
This is way better.

[Kairos]

Slight update.

I made a DIN13 to SCART-RGB cable according to CZIETZ's design published here. This cable though differs from the CZIETZ design in that it entirely OMITS connecting the signal from pin 8 on the Atari DIN13 port.

It didn't work.

I instead connected pin 8 on the Atari DIN13 port to a LED that I housed in the SCART connector. The LED is coming on, so there IS in fact a +12V signal coming from it.

The very same cable works nicely on an STE connected to the same teve.

My assumption that the lack of +12V from the 1040STF was causing the trouble, was wrong.

To sum it up:
It seems that there's nothing wrong with the cable itself.
The teve is working nicely with the STE and the same cable.
The 1040STF does indeed provide a +12V signal.
The 1040STF works nicely with a monochrome monitor.

It appears that there either might be something wrong with the 1040STF, or that the 1040STF's pairing to that specific teve model won't work.

[mpattonm]

Does it work if you force your TV to RGB SCART via remote?

[Kairos]

On the STE, the switching of SOURCE via the remote works.
Not on the 1040STF.

[siriushardware]

Sorry but I have not read the whole thread:

When using a SCART input on a monitor or TV, there are two necessary steps: First of all you select SCART as the input, but secondly you have to select the input mode used by SCART, with a choice of Composite Video (which will be the default if you do not choose otherwise) and RGB input, which you normally have to specifically select either by going into the TV's menus and telling it that you want the SCART input to be RGB (not Composite) or by applying the control voltage to pin 8 which informs the TV that it should use RGB input mode on SCART, and not Composite on SCART.

If you do not take either of the above steps to place a SCART input into RGB mode, it will be operating in Composite Video input mode by default.

The 1040 STF (without modulator) probably does not output a Composite Video signal on the monitor socket, only RGB, and I suggest that this, combined with the fact that the SCART input is not being set to RGB mode, is why the STF is not working. The STe outputs a Composite Video signal on the monitor socket so it will work when the SCART input is selected - but only in Composite mode.

If the display / TV can not be forced to use RGB mode on SCART by internal menu settings (not all of them can) does it have a USB socket on it? If so you could power a small DC-DC converter from the USB socket to generate the higher switching voltage required to put the SCART input into RGB mode.

[siriushardware]

This is the kind of thing I mean - apply 5V input from a USB socket on the display, and use one of these to generate the 12V required to switch the SCART input over to RGB input mode.

https://www.ebay.co.uk/itm/185306590837

[siriushardware]

Actually I have just noticed this over on the Wikipedia entry for SCART

Code: Select all

Pin 16		
RGB-selection voltage up
0–0.4 V → composite
1–3 V → RGB

So you need only force pin 16 to more than 1V in order to switch the SCART input to RGB input mode. A simple resistor between the +ve output terminal of a USB socket on the display and pin 16 in the SCART plug would do it.

The method above (using a DC-DC step up converter) still seems to apply if you want to automatically select 4:3 aspect ratio as well, although this is something which you usually can select from the TV / Display's remote and menus.

Code: Select all

Pin 8		
Status & Aspect Ratio up
0–2 V → off
+5–8 V → on/16:9
+9.5–12 V → on/4:3

[elliot]

I was about to ask, what would happen if you put 9v into that pin from a 9V bat (the square fire hazards)? Out of spec but will prob still work.

[siriushardware]

You would need to measure the resistance of the SCART pin 16 input on the display down to 0V. Input terminals on video inputs including SCART are often terminated with a 75R resistor internally, so a battery driving such a low resistance would not last very long and you could even burn out the internal 75R resistor in the display, if the battery voltage is too high.

This low 75R impedance is also the reason why schemes using the +12V out from the monitor to pin 16 of SCART often do not work the way you would expect, because there is a 1K resistor inline with that signal inside the ST. If you put 12V through a resistance divider consisting of 1K + 75R, there is not much left of the 12V by the time you get to the midpoint of the divider, not enough to trip the SCART input into RGB mode.

One possible solution is to modify the ST internally so that it outputs a sufficiently powerful drive signal on pin 12, in other words, reduce the size of the 1K resistor to something less than that. Of course then, the lead / cable will only work with that particular ST.

[siriushardware]

I forgot to say above that if you do want to try using a battery to test / try the RGB mode switching feature of SCART pin 16, a 1.5V battery will do since the voltage applied to pin 16 only needs to be between 1.0V and 3.0V to select RGB-in mode on SCART. But note again: If pin 16 has a 75R termination resistor, the battery will not last very long.