Help with Composite out

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bwinkel67
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Help with Composite out

Postby bwinkel67 » Mon Jan 20, 2020 2:05 am

So I have a US QL and after some investigating I found that I could use pin 2 (GND) and pin 3 (Composite monochrome) off of the RGB connector to get a pretty nice monochrome TV and Monitor picture on my SuperSonic monitor (it's a cheap Walmart monitor that has every connection imaginable in the US: VGA, HDMI, Component, Composite, and RF). The RF signal also works but in TV mode it washes out the colors a bit and in Monitor mode it goes to a grainy monochrome.

As I posted elsewhere, the US QLs don't seem to support pin 1 (Composite PAL) and instead feed a 5 volt signal on that pin instead. I have no idea why...anyone???

In any case, I had planned a quick mod to run a wire from pin 9 of the MC1733 and connect it to pin 1 of the RGB connector, cutting whatever trace it had that was giving it 5 volts and thus giving pin 1 that composite PAL signal it is supposed to have. I never got this far (i.e. I didn't completely remove the motherboard) so I don't remember what sort of factory hacks are on the underside (I took it apart back in October but can't recall what I saw) but through a vent I can already see a black wire near that area that is jumping something so I wonder if that is supplying the 5 volts. The reason I aborted is that I briefly jumped pin 9 of the IC and pin 2 of the connector and hooked it to composite on two different TV's (one was the SuperSonic TV/Monitor combo and the other was an Emerson TV/DVD combo). The composite PAL TV signal wasn't that much better than the RF NTSC one (whereas the composite monochrome was crisp). When I tried Monitor mode, on the SuperSonic I got a similar picture than what RF gave me in TV mode (grainy monochrome) and on the Emerson I got nothing.

So, what do I need to add to get a pristine Composite picture off of the MC1733's pin 9? I saw a Spectrum hack on YouTube where the guy added a capacitor to the Composite line (as he's changing the Astec modulator) but I read a link from qlforum where it was just a rewiring with no capacitor. It's surprising because Composite monochrome gives such a crisp picture (not just ok but really good).


Martin_Head
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Re: Help with Composite out

Postby Martin_Head » Mon Jan 20, 2020 10:27 am

Maybe you have a fault in the colour modulator circuit of the MC1733. This may not effect the black and white signal.

it's a cheap Walmart monitor that has every connection imaginable in the US: VGA, HDMI, Component, Composite, and RF
By component do you mean RGB. If so, can you use that instead. You may need to add some resistors if the monitors RGB inputs are 1 volt rather than the QL's 5 volt output. Likewise the sync signals.


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Chr$
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Re: Help with Composite out

Postby Chr$ » Mon Jan 20, 2020 12:56 pm

I bought a QL from Spain last month and it came with a mono monitor with just a composite-in and a cable that plugs in to the RGB connector on the QL. The QL was standard and the cable doesn't appear to have any extras like caps or resistors. And it gives me a nice b/w picture on a newer TV. So it is possible! Would you like me to check which pin goes to the comp signal and which is gnd?

I'm actually using it right now (with a German QL, which I believe is the same as a US one) because I have another going to the same TV's scart port and it means I can use the remote control to switch from one QL to the other.


Collector of original and some new QL related computers, accessories and software even though I don't understand how any of them work.
Original BBQL's: 2x German, 1x UK model (plus quite a bit of other old stuff)
Custom AT cased QL system with Gold Card, Qimi mouse, Hermes and MFM HDD
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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Mon Jan 20, 2020 7:31 pm

Martin_Head wrote:Maybe you have a fault in the colour modulator circuit of the MC1733. This may not effect the black and white signal.

it's a cheap Walmart monitor that has every connection imaginable in the US: VGA, HDMI, Component, Composite, and RF
By component do you mean RGB. If so, can you use that instead. You may need to add some resistors if the monitors RGB inputs are 1 volt rather than the QL's 5 volt output. Likewise the sync signals.


I think it's called "luma based analog component video" and wants Y, Pb, and Pr which are not direct R, G, B connections. From wiki, Y carries luma, Pb carries the difference between B, the blue signal, and Y, the luma, (B - Y) and Pr carries (R - Y). So I don't think you can do that with just cabling and resistors.


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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Mon Jan 20, 2020 7:43 pm

Chr$ wrote:I'm actually using it right now (with a German QL, which I believe is the same as a US one) because I have another going to the same TV's scart port and it means I can use the remote control to switch from one QL to the other.


Yes, that would be great. I'm guessing it is using pin 3 and pin 2.

Martin mentioned that the QL's RGB are 5 volts so does that mean the signal strength varies between 0 and 5. Pin 1 is basically high at 5 volts all the time, i.e. it doesn't vary. I'm guessing, if that was done on purpose, one reason the factory might have done that back in the 80's is because the US didn't have PAL (and likely never would) so it wold have been useless for pin 1 to give a PAL composite. I also notice that some RGB conversion cables reference an outside 5 volt source and am wondering if that's why pin 1 supplied it since it was not being used otherwise. Or it could be they just set the voltage on high because they hated to have it unused. I think on the DB9 RS232 connectors they do the same thing and shoot out I believe 12 volts on pin 9 which is not standard for RS232 DCE or DTE connectors. The UK 6 pin pseudo RJ connectors has 12 volts come out of pin 6.

Of course the other thing could be somehow my unit has a short that only effects pin 1 on the RGB as otherwise it seems to be running fine. I did get color PAL off of pin 9 on the MC1733 chip so I know that's working, it was just so washed out that I didn't bother running a bodge wire from it to pin 1 and cutting pin 1's trace.


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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Mon Jan 20, 2020 7:55 pm

So thinking a bit more on it, and something Martin pointed out with regard of the higher voltages for R+G+B, perhaps the PAL composite signal off of pin 9 on the MC1733 has too much voltage. Adrian Black is one of my favorite YouTube'rs and he did a mod on a cheap $10 hand held game where he put a 47 ohm resistor on the out signal of the composite (he tested various ohms to see what was best). You can see the video below (at 8 minute mark):

https://www.youtube.com/watch?v=ceI4CeIN1SQ

He said the high voltage washed out the signal and gave much worse color. So perhaps my next step is to try again and see if, adding a resistor inline I can improve the output of the composite color form the chips pin 9. If so then I'm definitely adding a bodge wire to regain pin 1 on my RGB connector.


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Re: Help with Composite out

Postby Martin_Head » Tue Jan 21, 2020 10:37 am

I had a look at the data sheet for the MC1377. And it says that pin 20 of the chip should be connected to ground for NTSC and left floating for PAL. You might want to check with a multi meter that it is grounded. In case it is actually working in PAL which would cause you problems. Also check the Xtal X3. In the UK it's 4.433619MHz. I think it's a different frequency in the US. UK QL's used a UM1233 UHF modulator, I don't know if the US one's are different.

As for the component inputs of the monitor I fount this RGB converter http://www.tg16pcemods.com/rgb-to-component-converter-v-20.html
Do a search for 'rgb to component converter'


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Chr$
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Re: Help with Composite out

Postby Chr$ » Tue Jan 21, 2020 3:18 pm

bwinkel67 wrote:Yes, that would be great. I'm guessing it is using pin 3 and pin 2.

No, on my Spanish mono composite vid lead the signal is connected to pin 1 of the RGB plug and the gnd to pin 3.


Collector of original and some new QL related computers, accessories and software even though I don't understand how any of them work.
Original BBQL's: 2x German, 1x UK model (plus quite a bit of other old stuff)
Custom AT cased QL system with Gold Card, Qimi mouse, Hermes and MFM HDD
PC with QXLII card installed
Q68 present, but not setup yet

Other hobbies include writing chick lit on a chiclet.
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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Tue Jan 21, 2020 10:14 pm

Chr$ wrote:
bwinkel67 wrote:Yes, that would be great. I'm guessing it is using pin 3 and pin 2.

No, on my Spanish mono composite vid lead the signal is connected to pin 1 of the RGB plug and the gnd to pin 3.


I'm a bit confused. Pin 2 is ground on the RGB plug so the only combos ought to be 1+2 or 3+2. What does 1+3 give you since that connects (according to the plug diagram) composite PAL and composite monochrome?


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Chr$
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Re: Help with Composite out

Postby Chr$ » Tue Jan 21, 2020 11:17 pm

Unless European's were different. In case there is any confusion on the pin numbering....

20200122_001129_resized.jpg


I checked again just now. 1 goes to the centre of the RCA type comp plug, 3 to the outer ring.


Collector of original and some new QL related computers, accessories and software even though I don't understand how any of them work.
Original BBQL's: 2x German, 1x UK model (plus quite a bit of other old stuff)
Custom AT cased QL system with Gold Card, Qimi mouse, Hermes and MFM HDD
PC with QXLII card installed
Q68 present, but not setup yet

Other hobbies include writing chick lit on a chiclet.

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