EDIT: Commodore 1084 troubles

[zedrein]

UPDATE: I received my 1084 on friday and wouldn't you know it, the damn thing doesn't work properly!

The picture will display for a few minutes and then randomly shut off. Sometimes I can lightly tap the sides and it will come on, but not very often. This is strange because the sound works fine, so the whole unit doesn't turn off, just the picture portion.

One good thing about this transaction was the seller completely refunded me and didn't even make me return the monitor--but I still have a useless display!!

If anyone has any ideas why this is happening, I'd love to hear them, otherwise could you link me up to a quality display that I can use my refunded money to buy?

[kendrick]

As far as your ground problem goes? Back at the console end, all the ground wires connect to the same negative voltage terminal. You can safely connect three separate lines to your one ground wire and get the desired effect.

[zedrein]

Oh perfect, thanks for the reply.

Say, have you heard of a SNES RGB cable with the audio potion already brought out into 2 RCA cables? That would great to get a hold of because then I would only have to swap out the connector for my display!

[zedrein]

Oh jeez...so I am just finding out that my SCART cable only brings out composite sync on the composite video line...so now I'll have to get a LM1881 chip?

I hate to complain, but just this evening I've already bought:

1 DIN 6 connector, $11.00 w/shipping

12 capacitors, only $3.00

1 SCART cable, $11.00

and now I just picked up a LM1881 that was over $10

Man this is really adding up, I hope it's worth it!

[Drakon]

Oh jeez...so I am just finding out that my SCART cable only brings out composite sync on the composite video line...so now I'll have to get a LM1881 chip?

I hate to complain, but just this evening I've already bought:

1 DIN 6 connector, $11.00 w/shipping

12 capacitors, only $3.00

1 SCART cable, $11.00

and now I just picked up a LM1881 that was over $10

Man this is really adding up, I hope it's worth it!

hoo boy, I REALLY don't get why people go through all this trouble using a lm1881.  If you just do what I do and actually research the snes multi-av pinout on the back, the US and super famicom models have a "composite SYNC" pin on them.  So if you use that pin, all you need is a 100uf 10v capacitor and you get perfect sync.  Saves you a lot of money.  It was a bit harder to figure out the SNES than figuring out the sega genesis (straight wires no capacitors needed for the genesis).  But still it was way easier than building a sync seperator circuit.  Really the only advantage to building a lm1881 circuit is if you somehow have a piece of hardware that for some stupid reason doesn't have a sync wire and only has composite video, then you WILL need the LM1881.  But unless you're running a PAL snes then you don't need to go through all this trouble.  The only annoying thing I found is every website I went to told me about needing capacitors on the rgb lines of the US/jap snes.  But NONE of them mentioned anything about the composite sync pin needing one.  I just took a guess and it turned out I was right.

[RGB32E]

The only annoying thing I found is every website I went to told me about needing capacitors on the rgb lines of the US/jap snes.  But NONE of them mentioned anything about the composite sync pin needing one.  I just took a guess and it turned out I was right.

Connecting a series capacitor on the compsite sync output from NTSC SNES systems isn't a requirement for all monitors though (not needed for my Sony PVM).  However, I had to connect a capacitor on the composite sync output from my Genesis 2 to get the correct image via RGBS on my PVM (similar type of issue). 

BUT, if Zedrein is using pre-built SCART cables instead of custom ones, a LM1881 is still required.... 

[Drakon]

The only annoying thing I found is every website I went to told me about needing capacitors on the rgb lines of the US/jap snes.  But NONE of them mentioned anything about the composite sync pin needing one.  I just took a guess and it turned out I was right.

Connecting a series capacitor on the compsite sync output from NTSC SNES systems isn't a requirement for all monitors though (not needed for my Sony PVM).  However, I had to connect a capacitor on the composite sync output from my Genesis 2 to get the correct image via RGBS on my PVM (similar type of issue). 

BUT, if Zedrein is using pre-built SCART cables instead of custom ones, a LM1881 is still required.... 

wow that's weird.  My genesis works fine on my encoder

[viletim]

The only annoying thing I found is every website I went to told me about needing capacitors on the rgb lines of the US/jap snes.  But NONE of them mentioned anything about the composite sync pin needing one.  I just took a guess and it turned out I was right.

Putting a capacitor in series with a c-sync output connected to a c-sync input simply isn't required. It's more likely you were doing something wrong to start with.

[Drakon]

The only annoying thing I found is every website I went to told me about needing capacitors on the rgb lines of the US/jap snes.  But NONE of them mentioned anything about the composite sync pin needing one.  I just took a guess and it turned out I was right.

Putting a capacitor in series with a c-sync output connected to a c-sync input simply isn't required. It's more likely you were doing something wrong to start with.

uhm....no.  The only difference between my snes working and not working on my encoder board is a capacitor on the composite sync line.  My genesis works on my encoder board when wired straight, but my snes doesn't work without the capacitor

[ken_cinder]

He's not necessarily doing something wrong viletim. I had to put a cap on my sync line for my arcade PCBs to display on my PSOne LCD, but don't require it on either of my TVs.

Without a small cap on the sync line for my PSOne LCD, the image refused to sync. Such a minor deviation that holding the wires at either end with my fingers, would cause it to sync.

[viletim]

Without a small cap on the sync line for my PSOne LCD, the image refused to sync. Such a minor deviation that holding the wires at either end with my fingers, would cause it to sync.

I've never owned a PSOne LCD but are you sure that this "sync line" is actually a TTL composite sync input? Would be strange if it were so, because no Playstation outputs composite sync.

[ken_cinder]

http://www.gamesx.com/avpinouts/psxav.htm

Composite Video on that pin OUT, and Jamma sync is composite sync. Obviously the PSOne LCD can accept straight c-sync.
The PSOne itself has no bearing on what I just said though....a display device is a display device, and underneath the connectors this thing has no idea what it's hooked up to. Uses a Samsung LCD panel too, not anything made by Sony.

Actually, the LCD appears to use RGBS from the PSOne if I recall.
The only reason there is even a comp vid line is because of the AUX 3.5mm "camcorder" plug. (Which I infact have cables for and have hooked my Cube\Xbox\PS2 up with)

[viletim]

The PSOne itself has no bearing on what I just said though....a display device is a display device, and underneath the connectors this thing has no idea what it's hooked up to. Uses a Samsung LCD panel too, not anything made by Sony.

I found a picture on one of these displays and I can see that it has been designed specialy for the Sony PSOne. I don't have a PSOne either but I've been led to believe that all Playstations A/V ports are the same. My Playstation doesn't have a composite sync output (I've just confirmed this), so neither should the PSOne.

Do you still have the original connectors assembley from this display? Follow the wire from this "composite sync" point to the PSX A/V connector. Then look it up on the gamesx pinout to find out what it really is. I'd bet it's either composite video (pin 6) or luminance (pin 5) because no other signal contains sync information.

[ken_cinder]

My sync is on the composite video pin (According to the PSOne connector), and like I said the PSOne LCD may have been designed specifically for the PSOne but the screen and it's controller don't know what they are hooked up to.

The line from the composite video pin on the PSOne connector runs to the decoder but ALSO come in from the 3.5mm jack and goes to the same place.
If you look at a PCB, there are markings for "EXT" (External) for these inputs that lead to the same point.

WHY would the LCD use composite video, when a PSOne can at least output S-Video? Why are people hooking these LCDs up to their computer video cards and using things like Powerstrip to use them as little media displays?
Anyway, you can see the image on the screen and compare it to a comp hookup and know for a fact it's not outputting composite. (I've even hooked a PSOne up through both means, and the EXT input is most definitely different)

I think you're seriously confusing the whole fact that this LCD, is just an LCD....and not an extension of the PSOne itself. Take the PSOne style shell off it, unplug the PSone connector(s) and you have....an LCD screen with no reference to the fact it is for use on the PSOne.
If this wasn't the case, why would an explicitly NTSC board have pinouts for R/G/B at all? (The Samsung lts500q1-gf1 is an NTSC only board, the PAL model uses a different PCB)
The LCD has pinouts for EVERYTHING the PSOne is capable of spitting out, in any region, but most likely uses regional PCBs because of the decoder used for EXT input.

Infact, check this out. You can't feed composite video over the connection the PSOne connector is on - http://home.iprimus.com.au/kumsijo/ (The connector points I make use of)
Stupid him, could have used the EXT connector to achieve this though, as that runs to a decoder on the PCB anyway.......though maybe this doesn't exist on the PAL board.

Why would this go against what I'm saying? My sync is already seperate!

[viletim]

You are ignoring the electrical properties of the signals.
TTL C-Sync must meet TTL specifications, logic low = 0-0.8v logic high = 2.4-5v.

Composite video is treated as a transmission line with both ends at the same impedance. The sync portion of the signal is small - 0.3Vpp typical. It is 'stripped' by clamping the lowest point of the signal to a referance voltage and comparing it with another referance voltage some tens of milivolts higher.

A TTL signal expects to go into a high impedance gate input, not a 75 ohm transmition line. When you connect it to a low impedance input the signal is likely to distort. A sync stripper only cares about the botom ~100mVpp of the signal, if this bit is distorted it's not going to work properly.

It's a bit like a stereo audio amplifier. It has three outputs, one for tape recorder output, one for headphones, and one for speaker boxes. All three signals contain exaclty the same information. You understand what happens if you start swapping them around? It's possible to connect the speaker output to a tape deck input by placing some passive components on the line. See the similarity? But in the case of sync signals the structure of the signal is more important than the power dissipated.

[viletim]

-

[ken_cinder]

Why are most things I read about that tie into the RGB and Sync (Composite video according to PSOne pins) working without adding anything to the lines when using a composite sync? Why do the RGB lines exist at all, if no sync pin exists?
The decoder on the PCB must then, strip sync itself no? I've seen people hook composite video up to that pin for sync, and feed RGB on the other pins and it just works.

I've tried hooking other things up (PC video card, like described above and other things), and have not required a cap or anything on the line, but my arcade PCBs require one.

[viletim]

Why are most things I read about that tie into the RGB and Sync (Composite video according to PSOne pins) working without adding anything to the lines when using a composite sync?

People are less to boast about failure than success? I don't know... It depends entirely on the composite sync output circuitry of any particular device. It is entriely possible to make a composite sync output that is guaranteed to work when connected to either a composite video or composite sync input. This isn't usualy a design consideration though.

Why do the RGB lines exist at all, if no sync pin exists?

Historical reasons mainly. A legacy of SCART, which is still the most common RGB connection in the world. It has no dedicated sync input because when it was designed it was though the only time anynody would want to use RGB video is for a video overlay of existing composite video (for subtitles, etc). All TVs are capable of stripping sync of the video signal so it's no problem.

The decoder on the PCB must then, strip sync itself no? I've seen people hook composite video up to that pin for sync, and feed RGB on the other pins and it just works.

Definately.

I've tried hooking other things up (PC video card, like described above and other things), and have not required a cap or anything on the line, but my arcade PCBs require one.

As I said above, it varies quite a lot between devices. A good example of something that does not work most of the time is a Sega Mega Drive II. I've attached photos of the composite sync waveform lightly loaded with a 10k resistor (to simulate being connected to a C-sync input) and heavily loaded with a 75 ohm resistor (to simulate being connected to a c-video input).

In the first picture the oscilloscope is set to 1V per division (there's also a composite video signal on the second channel for size comparison). In the second it's set to 50mV per division. Notice the signal is mostly noise after being loaded with 75 ohms.

[ken_cinder]

So you're basically telling me that I CAN feed sync this way, it's just not designed to work that way?

I don't understand your explanation with regards to the RGB lines though. NTSC video standards have never included SCART, and there are 2 different models of the PSOne LCD (NTSC and PAL respectively).
Maybe they use identical PCBs, with minor component changes?

Finally if there is no sync pin on the LCD, what is the PSOne outputting when hooked up to the LCD? Comparing quality via the EXT 3.5mm input (3 RCA composite video + stereo audio) and a direct connection to the PSOne plug, I KNOW it's not composite video over the PSOne plug.

I get the feeling it,s using the RGB pins and stripping sync from the composite video lines. Afterall, the panel is natively RGB, and we know the decoder can strip the sync itself. The video looks amazingly sharp and vivid, it must be at least S-Video (But why the heck do the RGB lines run right to the connector then?)

Oh and another thing, could I then tie into the sync line AFTER the decoder to hook pure sync up to, so as to not require a cap and have the cleanest possible image?

[viletim]

So you're basically telling me that I CAN feed sync this way, it's just not designed to work that way?

Pretty much, yeah.

I don't understand your explanation with regards to the RGB lines though. NTSC video standards have never included SCART, and there are 2 different models of the PSOne LCD (NTSC and PAL respectively).
Maybe they use identical PCBs, with minor component changes?

Well, SCART has nothing to do with PAL or NTSC. It's a french (who are SECAM) idea which propagated throughout Europe. There's also the almost-but-not-quite SCART japanese 21 system. All I can say is that pretty much all TVs with RGB inputs accept composite video as a sync source, and every popular game console outputs composite video as well as RGB. The PAL PSOne LCD probably has differnet video decoding circuitry, but the c-video input will still be a c-video input.

Finally if there is no sync pin on the LCD, what is the PSOne outputting when hooked up to the LCD? Comparing quality via the EXT 3.5mm input (3 RCA composite video + stereo audio) and a direct connection to the PSOne plug, I KNOW it's not composite video over the PSOne plug.

I get the feeling it,s using the RGB pins and stripping sync from the composite video lines. Afterall, the panel is natively RGB, and we know the decoder can strip the sync itself. The video looks amazingly sharp and vivid, it must be at least S-Video (But why the heck do the RGB lines run right to the connector then?)

That's exactly right. It's taking the video from the RGB signals and taking the sync from the composite video signal. All the video information in the composite video signal is disregarded. In fact the composite video signal need not contain any video information at all. I think this is what causes so much confusion - a composite video signal which does not contain anything but sync information, strictly speeking, is not a composite video signal anymore but just a sync signal. But it's a sync signal with the same electrical characteristics as a video signal.

Oh and another thing, could I then tie into the sync line AFTER the decoder to hook pure sync up to, so as to not require a cap and have the cleanest possible image?

It should be possible but it depends on the design of the display device. There's really no need to do that though. Sync either works or doesn't and has no effect in picture quality. To convert TTL c-sync to 75R c-video you can use passive components (resistors and capacitors) but the optimum values vary depending on the source. Sometimes it's impossible to do it this way (in the case of the Megadrive II and it's unbuffered c-sync signal). An active (powered) circuit, typically using a 74LS or 74HCT logic chip is guarenteed to work every time. I can post some circuits if anybody's interested.

Unfortunately, it's virtually impossible to design a circuit that is guarenteed to sync from any TTL sync or c-video without requiring a switch of some kind select which one is being used.

EDIT: fixed the quotes