Help with Composite out

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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Wed Jan 22, 2020 12:04 am

The connector for the QL (and maybe in general for this type of connector) has weird numbering. So you are 3 and 2 which should give composite monochrome.

monitor connections.jpg


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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Wed Jan 22, 2020 2:19 am

Martin_Head wrote: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'


First, thank you for taking the time to look at the data sheet, that's very helpful. I will check that. What is interesting is that wen I connect pin 3 and pin 2 on the RGB connector I get composite monochrome NTSC and when I grab pin 9 off of the MC1377 and pen 2 on the RBG connector I get composite color PAL. This seems to be to spec of what the connector configuration says. The picture was just crappy (not a lot better than RF) -- I guess I didn't think that maybe PAL on my monitor would underperform NTSC through composite. Of course monochrome is sending less info.

So you are saying if I ground pin 20 I should perhaps get composite color NTSC and that perhaps it will give a more crisp picture? I will definitely try that. I assume to test it I can just check if MC1377 pin 20 and RGB pin 2 (GND) are on the same circuit?

BTW, I love the fact these old computer have so many variations on them that a pin on a chip here or there configured one way or the other gets you different outputs. Not so easy to do on modern equipment and adds joy with these older computers.


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Re: Help with Composite out

Postby Martin_Head » Wed Jan 22, 2020 10:52 am

bwinkel67 wrote:
Martin_Head wrote: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'


First, thank you for taking the time to look at the data sheet, that's very helpful. I will check that. What is interesting is that wen I connect pin 3 and pin 2 on the RGB connector I get composite monochrome NTSC and when I grab pin 9 off of the MC1377 and pen 2 on the RBG connector I get composite color PAL. This seems to be to spec of what the connector configuration says. The picture was just crappy (not a lot better than RF) -- I guess I didn't think that maybe PAL on my monitor would underperform NTSC through composite. Of course monochrome is sending less info.

So you are saying if I ground pin 20 I should perhaps get composite color NTSC and that perhaps it will give a more crisp picture? I will definitely try that. I assume to test it I can just check if MC1377 pin 20 and RGB pin 2 (GND) are on the same circuit?

BTW, I love the fact these old computer have so many variations on them that a pin on a chip here or there configured one way or the other gets you different outputs. Not so easy to do on modern equipment and adds joy with these older computers.
I would expect that a US QL would not generate a PAL signal at all. I assume when you refer to a 'composite color PAL' signal, you are just referring to the name on the socket connector.

I was wondering if your QL was generating a PAL signal, instead of an NTSC one. That's why I suggested checking the resistance of pin 20 of the MC1377 to ground. If it's not a short circuit, then the MC1377 would be generating a PAL signal, which I don't expect an NTSC television would be very happy about. Also what version of QDOS do you have. I don't know of any US version other than JSU. If you have something else, then maybe it's not a US QL. Here http://www.sinclairql.net/build_standards.html is some information I found about American QL serial numbers.


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bwinkel67
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Re: Help with Composite out

Postby bwinkel67 » Wed Jan 22, 2020 4:34 pm

Martin_Head wrote:I was wondering if your QL was generating a PAL signal, instead of an NTSC one. That's why I suggested checking the resistance of pin 20 of the MC1377 to ground. If it's not a short circuit, then the MC1377 would be generating a PAL signal, which I don't expect an NTSC television would be very happy about. Also what version of QDOS do you have. I don't know of any US version other than JSU. If you have something else, then maybe it's not a US QL. Here http://www.sinclairql.net/build_standards.html is some information I found about American QL serial numbers.


Yes, my QL is generating both NTSC and PAL. The monitor/TV shows the signal it receives in the left upper corner for a few seconds. Monochrome composite is NTSC and when I grab pin 9 on MC1377 it is color composite PAL. My unit uses JSU ROM so it is true US version. So would that mean if I ground pin 20 it won't matter (or pin 20 is already grounded). Won't get to taking it apart again until the weekend :-/


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Re: Help with Composite out

Postby Martin_Head » Thu Jan 23, 2020 10:12 am

bwinkel67 wrote:
Martin_Head wrote:I was wondering if your QL was generating a PAL signal, instead of an NTSC one. That's why I suggested checking the resistance of pin 20 of the MC1377 to ground. If it's not a short circuit, then the MC1377 would be generating a PAL signal, which I don't expect an NTSC television would be very happy about. Also what version of QDOS do you have. I don't know of any US version other than JSU. If you have something else, then maybe it's not a US QL. Here http://www.sinclairql.net/build_standards.html is some information I found about American QL serial numbers.


Yes, my QL is generating both NTSC and PAL. The monitor/TV shows the signal it receives in the left upper corner for a few seconds. Monochrome composite is NTSC and when I grab pin 9 on MC1377 it is color composite PAL. My unit uses JSU ROM so it is true US version. So would that mean if I ground pin 20 it won't matter (or pin 20 is already grounded). Won't get to taking it apart again until the weekend :-/

NTSC and PAL are two methods of encoding a colour signal onto a composite monochrome signal (PAL being an improved, but not compatible version of NTSC). The QL can produce one or the other, but not both at the same time. It sound like your monitor/TV may support both NTSC and PAL (check it's specifications). Maybe if it does not see a colour signal (composite monochrome) it defaults to displaying NTSC. As it says composite PAL when you supply a colour signal, maybe if if does not recognize the signal as NTSC, it just assumes it's PAL.

There may be a couple of things going on here. There could be something wrong with the colour encoder in the QL not producing a correct NTSC signal, or perhaps the monitor/TV does not like the NTSC signal the QL produces, and assumes it's PAL and tries to display it as a PAL signal, when it is not.

Have you tried another make of monitor/TV with the QL.


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Re: Help with Composite out

Postby janbredenbeek » Thu Jan 23, 2020 11:02 pm

Martin_Head wrote:NTSC and PAL are two methods of encoding a colour signal onto a composite monochrome signal (PAL being an improved, but not compatible version of NTSC). The QL can produce one or the other, but not both at the same time. It sound like your monitor/TV may support both NTSC and PAL (check it's specifications). Maybe if it does not see a colour signal (composite monochrome) it defaults to displaying NTSC. As it says composite PAL when you supply a colour signal, maybe if if does not recognize the signal as NTSC, it just assumes it's PAL.

It's not just the encoding that is different. Both NTSC and PAL use a subcarrier for the colour signals, but at a different frequency. NTSC at 3.58 MHz, PAL at 4.43 MHz. This is because of the difference in number of lines and frame frequency (525 lines/60Hz for NTSC, 625 lines/50Hz for PAL). So if you change from PAL to NTSC or the other way, you have to change the crystal frequency (and probably some RC/LC filter networks around the 1377 too).

Jan.


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Re: Help with Composite out

Postby bwinkel67 » Fri Jan 24, 2020 3:02 am

janbredenbeek wrote:
Martin_Head wrote:NTSC and PAL are two methods of encoding a colour signal onto a composite monochrome signal (PAL being an improved, but not compatible version of NTSC). The QL can produce one or the other, but not both at the same time. It sound like your monitor/TV may support both NTSC and PAL (check it's specifications). Maybe if it does not see a colour signal (composite monochrome) it defaults to displaying NTSC. As it says composite PAL when you supply a colour signal, maybe if if does not recognize the signal as NTSC, it just assumes it's PAL.

It's not just the encoding that is different. Both NTSC and PAL use a subcarrier for the colour signals, but at a different frequency. NTSC at 3.58 MHz, PAL at 4.43 MHz. This is because of the difference in number of lines and frame frequency (525 lines/60Hz for NTSC, 625 lines/50Hz for PAL). So if you change from PAL to NTSC or the other way, you have to change the crystal frequency (and probably some RC/LC filter networks around the 1377 too).

Jan.


Yes, that's what I thought, with regard of the crystal frequency. I'm assuming the QL doesn't have both crystals on that motherboard (that would be cool but very odd) so either I have a PAL system or an NTSC one. I definitely know I have an NTSC one (I've had it since 89) because my RF works here in the US. My composite monochrome also works really well. My composite PAL does not (from the connector) and it shouldn't since it's a US system...instead I get a high 5 volts on that pin.

When I jumped the MC1733 on pin 9, that's when I got the weird behavior of getting a color picture in composite that wasn't that much better than the color RF one I get. The only other weirdness is that my monitor said it was PAL. As Martin pointed out, perhaps my monitor was doing something weird and it couldn't quite figure out what the signal was so it just said incorrectly PAL. Otherwise my QL would give both a color NTSC signal (over RF) and a color PAL signal (pin 9). And as nice as that sounds, form what I've read on other computers, as you said, it would need a different crystal to get the correct refresh rate.

Could it be something ungodly like trying to display a PAL signal at the NTSC frequency? Is that even possible? The monitor/TV I have, like I stated, is cheap -- a $99 Walmart item that I got for free. The bootup screen where it gives the SuperSonic logo is crisp. I haven't tried to plug VGA or HDMI into it but I bet it will do ok since it's just an LCD monitor that decided to add a TV tuner. It's the analog it seems to be struggling with, whether RF or composite.

In any case, I have both a RCA-2-HDMI and RCA-2-VGA converter box (they are those inexpensive square white boxes which I have like four of that up- and downscale to and from HDMI, VGA and RCA). What I recall from using them in the past is that they do recognize the difference between NTSC and PAL and can handle both and will also display which type it is briefly on the screen. So I will connect pin 9 of the MC1733 and ground to one of those two devices (unfortunately they are presently both at work not with me) to see what it thinks I'm getting. Maybe it's just a crappy color composite NTSC signal..I mean it has to exist, right, because isn't that what's being fed into the RF modulator? If I have an NTSC system somewhere I should be able to get NTSC composite color -- it's kind of what it looked like quality wise, just coming out of the TV's composite plug vs the coaxl for TV.

Thanks to all so far for the continued input. I keep getting some valuable tidbits from all of you so maybe eventually I'll figure it out. I did by an SCART-to-HDMI converter for $7 and will create a cable for it (330 and 390 resistor in all). Unfortunately I purchased a female SCART connector previously because I bought one of those cheap ($1.70) SCART-to-Composite boxes (eBay is treacherous for getting cheap stuff like that) that basically just rewires things but has no circuitry in (so since my RGB plug pushes 5 volts out on pin 1 that little non-coverter box will give me that same useless 5 vots on that yellow RCA connector). I haven't even gotten it yet but already know it's a waste because I saw a YouTuber taking it apart to show what's inside. So eventually I'll get an HDMI signal out of the RGB and hopefully that picture will be crisp. If the $7 one doesn't do it then I'll invest in the one that I see many people on this forum have (I think it's like $25) but at $7 it was worth a try.


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Re: Help with Composite out

Postby Martin_Head » Fri Jan 24, 2020 11:05 am

bwinkel67 wrote:When I jumped the MC1733 on pin 9, that's when I got the weird behavior of getting a color picture in composite that wasn't that much better than the color RF one I get. The only other weirdness is that my monitor said it was PAL. As Martin pointed out, perhaps my monitor was doing something weird and it couldn't quite figure out what the signal was so it just said incorrectly PAL. Otherwise my QL would give both a color NTSC signal (over RF) and a color PAL signal (pin 9). And as nice as that sounds, form what I've read on other computers, as you said, it would need a different crystal to get the correct refresh rate.


Can you clarify, as maybe I'm misunderstanding what's happening. If you use the the RF out of the QL. Do you get a colour picture, in the correct colours, on the monitor.
When you use pin 9 of the MC1377 (which should feed the RF modulator), do you get the same results as when using the RF output. Don't expect the picture quality to look a great deal better the the RF output.

A couple of other points come to mind that you might want to try. Is there a button, or a menu option on the monitor/TV for force it into NTSC mode when it says it's in PAL mode. Or a menu option that you can set that disables the auto selection ability, so that it's stuck in NTSC mode.

Also check the 12 volt power line in the QL. The 12V is used by the MC1377. I'm pretty sure that if the 12v is missing you get no colour output on the colour composite, or RF outputs. I don't know what may happen if the 12v is not 12v but something in-between.


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Re: Help with Composite out

Postby bwinkel67 » Fri Jan 24, 2020 9:46 pm

Can you clarify, as maybe I'm misunderstanding what's happening. If you use the the RF out of the QL. Do you get a colour picture, in the correct colours, on the monitor.


Yes, my monitor has a US TV tuner that can get both ATSC and NTSC and when I plug in RF I get the correct colors. Being RF, the signal is ok but shimmers and has a slight shadow. All normal and expected for RF, esp on an LCD screen (and cheap one at that).

When you use pin 9 of the MC1377 (which should feed the RF modulator), do you get the same results as when using the RF output. Don't expect the picture quality to look a great deal better the the RF output.


When I use pin 9 of the MC1377 and ground off of the RGB connector (pin 2) I seem to get a color PAL composite signal (when using the composite connector on the TV, my TV seems to briefly display what type of composite input it gets) that basically looks pretty close (as crappy) to my RF signal -- this was the surprise as I expected composite to be better. But it is composite as it plugs into the yellow RCA jack on the monitor (not the RF coaxl)

You said not to be surprised if the color composite is of similar quality as RF, but RF adds interference that makes the picture shimmer and adds shadows and I would not expect color composite to do that. I have some cheap handheld retro games that plug into composite port and the picture is crisp and no where near RF like. So even if the color composite picture in the QL is fed into RF I would think the source color composite should still be much crisper than the TV signal -- that's what monochrome composite gives me...the picture is very good.

So that's why I had the original thought...do I maybe need to add a resistor to pin 9 output? Do I need to turn down the composite color signal coming from the chip? Or is the interference form the RF modulator also interfering with pin 9? But if that's so, how does a circuit board trace running near the RF modulator then not get that same interference? In other words, if the MC1377 chip is that close to the RF modulator (which is housed in a protective metal box to hold in the interference) would we expect it to get interference on the composite and if so, how do we reduce/prevent it?

A couple of other points come to mind that you might want to try. Is there a button, or a menu option on the monitor/TV for force it into NTSC mode when it says it's in PAL mode. Or a menu option that you can set that disables the auto selection ability, so that it's stuck in NTSC mode.


No, the TV doesn't have much in the menu settings. Can adjust color, tint, etc, can add channels but that's about it. The TV feature of the monitor is rudimentary. However, those small white converter boxes I spoke off have switches on the side for PAL and NTSC when going from AV to HDMI (AV here means composite). So I am bringing them home today and trying that this weekend. I will post what it does.

Also check the 12 volt power line in the QL. The 12V is used by the MC1377. I'm pretty sure that if the 12v is missing you get no colour output on the colour composite, or RF outputs. I don't know what may happen if the 12v is not 12v but something in-between.


I will check. I recently was also playing with my DB9 serial port and verifying that pin 9 is 12 volts and indeed it measures 12 volts so the power supply is providing it. But I can check near the chip. Note that that I am getting all the colors I'm supposed to in RF mode.


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Re: Help with Composite out

Postby janbredenbeek » Fri Jan 24, 2020 11:31 pm

I haven't used my BBQLs much with composite colour, but I remember the picture quality was quite poor. Lots of dot crawl and definitely not suitable for a 80x25 screen. On the other hand, the monochrome picture is rock steady. I'm still using my green monochrome Philips monitor of almost 35 years with the BBQL! Only drawback is the screen size which is a bit on the small side at 12 inch ;)

Jan



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