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Issue using RGB on the Commodore 64 1084s


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Hello all. I have a Commodore 64 1084s monitor which works great via luma chroma s video for my retro consoles especially with monster s video cables. I would however like to access the RGB potential of this monitor if possible. I tried using a scart to 6 pin din cable to go from the monitor to a scart selector box and plugged in my Sega CDX's scart cable to said box. I hit the rgb switch on the 1084s and recieved a diagonally scrolling green picture. I made a You Tube video about this. Any suggestions?

 

https://youtu.be/X0pB-ON5vZk

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I would suggest you are missing the 1-3V signal that tells the TV to switch to RGB mode, which can cause this behavior, but you have a 1084 with separate RGB switch so that should not be the issue. Still I think something is not correct about the sync signal, and vaguely remember having suffered it myself, though I can't recall which combination of hardware did it. If your 1084 had been of the kind with a SCART input instead of the 6-pin DIN, it had made even more sense.

 

How is the cable made up, is a custom cable for the 1084 or something generic? I'm aware that 6-pin DIN has been used both on e.g. the Amstrad CPC computers and for video editing hardware, but I'm not sure if the pinout on the 1084 matches either of those so if you got a generic SCART to DIN cable, you would want to check the pinout to match the 1084.

 

Edit: Oh yes, there should be up to THREE switches on your 1084. One to select between CVBS and RGB, one to select analog or TTL RGB and one to select between composite and luma + chroma in case of CVBS mode. It could be that your 1084 is set to TTL mode but receives an analog signal which is much too weak. Try to find that switch and toggle it.

 

Edit 2: At least you're using the correct input, the 6-pin is for analog RGB and the 8-pin is for digital TTL RGB as used on e.g. C128, CGA, BBC Micro etc. I'm quite sure toggling those back side switches will help you in some way, assuming the cable is wired to match the pinout.

Edited by carlsson
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Hi! I got this cable online, I believe it was eBay so im assuming generic. My 1084s does not have a scart port. The scart port is covered. It has 9 or 8 pin din (which produces a blue screen), 6 pin din (analogue producing the rolling green picture), and Luma chroma that can do composite. There are two buttons on the back. One does luma chroma and the other i think is for VCR use. I'll try toggling. The rgb button is ob the front next to the volume and image knobs. The 1084s also has knobs on the back for picture size and centering.

Edited by Noel Comix
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Yup, the 1084 series comes in as many variations as Commodore had subcontractors to manufacture them. There are versions with two DIN jacks like yours, versions with one DIN and the SCART exposed, versions with a single DE9 that doubles as both TTL and analog RGB and perhaps combinations thereof.

 

Try the button you believe is for VCR. It might be so that the analog signal is ghosted through the circuitry when it is set to TTL mode (the other DIN jack).

 

Anyway, here are the full pinouts in case you need them:

Commodore_1084_pinout_DIN-rotated_large.

 

It can be compared to the Amstrad CPC pinout which is entirely different:

scart03.jpg

 

The BBC Micro has yet another pinout, but since its signals nominally are TTL level and would need a bunch of resistors to work on a SCART monitor, it probably is pointless to include it in the discussion, unless of course the cable you bought on eBay specifically is meant for a Beeb which would mean it weakens the signals to nearly nothing and throws them around. On the other hand I think if you got ground on the wrong pin, you would get pretty much nothing, instead of a single coloured image that is rolling or is displaced to the side.

 

The other video and camera applications I've seen with a 6-pin DIN don't handle RGB, rather other form of signals so your cable probably doesn't relate to those applications.

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Thanks. Hey I tried continuously hitting the button in the back and now the picture is scrolling vertically is off center and has a bit if blue mixed with the green. Kind of like watching scrambled cable back in the day lol.

Edited by Noel Comix
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Yup, the 1084 series comes in as many variations as Commodore had subcontractors to manufacture them. There are versions with two DIN jacks like yours, versions with one DIN and the SCART exposed, versions with a single DE9 that doubles as both TTL and analog RGB and perhaps combinations thereof.

 

Try the button you believe is for VCR. It might be so that the analog signal is ghosted through the circuitry when it is set to TTL mode (the other DIN jack).

 

Anyway, here are the full pinouts in case you need them:

Commodore_1084_pinout_DIN-rotated_large.

 

It can be compared to the Amstrad CPC pinout which is entirely different:

scart03.jpg

 

The BBC Micro has yet another pinout, but since its signals nominally are TTL level and would need a bunch of resistors to work on a SCART monitor, it probably is pointless to include it in the discussion, unless of course the cable you bought on eBay specifically is meant for a Beeb which would mean it weakens the signals to nearly nothing and throws them around. On the other hand I think if you got ground on the wrong pin, you would get pretty much nothing, instead of a single coloured image that is rolling or is displaced to the side.

 

The other video and camera applications I've seen with a 6-pin DIN don't handle RGB, rather other form of signals so your cable probably doesn't relate to those applications.

Thanks. Hey I tried continuously hitting the button in the back and now the picture is scrolling vertically is off center and has a bit if blue mixed with the green. Kind of like watching scrambled cable back in the day lol any ideas? Edited by Noel Comix
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Something strikes me: SCART uses RGB + composite sync while your 1084 uses RGB + separate horizontal and vertical sync! I don't know if feeding the C sync to both H and V sync would work or if you need a LM1881 sync separator.

Hmm you would know better than me. I'm not super tech savvy. My cable should have composite sync right? Where would I get a sync separator?

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Yes, your cable would carry the C sync from SCART. I'll see if I can do some testing though my setup is different. The LM1881 is a small chip you would have to solder, if it works and would make a difference. Can you link to the eBay auction to see if anything can be said about your cable?

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Yes, your cable would carry the C sync from SCART. I'll see if I can do some testing though my setup is different. The LM1881 is a small chip you would have to solder, if it works and would make a difference. Can you link to the eBay auction to see if anything can be said about your cable?

Sure! Here's the link to the cable I have... https://www.ebay.co.uk/itm/1m-Monitor-Lead-Cable-for-Acorn-BBC-Master-6Pin-DIN-to-TV-Monitor-RGB-Scart-/171294538937

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Uh oh... That cable is specifically for the BBC Micro. Entirely wrong pinout plus resistors that bring down levels from ~3V to 0.7V. You have no use at all of that cable.

 

Are you really located in Tokyo, Japan? I suppose someone could make a custom cable and sell you cheap.

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Uh oh... That cable is specifically for the BBC Micro. Entirely wrong pinout plus resistors that bring down levels from ~3V to 0.7V. You have no use at all of that cable.

 

Are you really located in Tokyo, Japan? I suppose someone could make a custom cable and sell you cheap.

Naa I'm in upstate New York state lol. I just like 80's anime bubblegum crisis. So any leads on where I could get the proper cable? Do you make them? I would be happy to pay for one. :)

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I'm not professional but could carve together one. I'll try to find a matching 1084 to test it with. SCART cables are $1 each and I think I've got extra 6 pin connectors. I'm a visitor at the hospital right now, I'll check later.

awesome! keep me posted! i'll happily buy one from you. Hope you're feeling okay.

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I'm not ill, I was just visiting. :)

 

But yes, I have located the required 6-pin DIN. I'll send you a PM later with details. I think our computer club may have one 1084 that exactly matches yours, otherwise I'll go by pinout and hope I don't mirror it.

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I'm not ill, I was just visiting. :)

 

But yes, I have located the required 6-pin DIN. I'll send you a PM later with details. I think our computer club may have one 1084 that exactly matches yours, otherwise I'll go by pinout and hope I don't mirror it.

Awesome! I'll be on the lookout for your message.

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It struck me that I still need a LM1881 or similar chip, which is something I can't obtain locally so it'll make it take a little longer. I'm still game, but if someone else steps in offering a similar service, I won't take offense. Also I'm afraid one would need an external 5-12V power source to that LM1881 chip, as it is not guaranteed that all your RGB SCART cables carry any significant voltages for RGB mode select / blanking which can be used to power the chip. I'll think a little about this.

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It struck me that I still need a LM1881 or similar chip, which is something I can't obtain locally so it'll make it take a little longer. I'm still game, but if someone else steps in offering a similar service, I won't take offense. Also I'm afraid one would need an external 5-12V power source to that LM1881 chip, as it is not guaranteed that all your RGB SCART cables carry any significant voltages for RGB mode select / blanking which can be used to power the chip. I'll think a little about this.

Cool. Keep me posted. Let me know what you think is reasonable. I have generic scart cables from amazon for my consoles. I use them on a scart to hdmi device sometimes. I think the 1084s gives better results via luma chroma so I've switched to that for the most part. Honestly I think you're my best bet for this lol. I don't know many people who are super aware of what scart cables are.

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If your monitor would've had composite sync input just like the SCART has (and there are 1084's made by Philips where the SCART is wired, so the question is what it looks like on the inside), it had been easy peasy.

 

I don't know which application that uses analog RGB and separated sync was the target for Philips (or Commodore, in case they ordered the monitors to spec instead of just getting what the manufacturer had to offer). The 8-pin one with TTL levels nicely matches the C128 80 column RGB output. The Amiga which has analog RGB outputs both composite and separated sync, so you can choose which signal to use. That pretty much sums up the market of Commodore branded computers at the time, even if we consider PC models with CGA that equal the C128 here.

 

Philips' own MSX and MSX2 models usually had built in SCART output in the case they did RGB at all. Perhaps some earlier Philips P2000C or similar? VG-5000? Not that it matters, perhaps there simply was a market demand for that at the time, or easier for the monitor to work with a separated sync.

Edited by carlsson
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If your monitor would've had composite sync input just like the SCART has (and there are 1084's made by Philips where the SCART is wired, so the question is what it looks like on the inside), it had been easy peasy.

 

I don't know which application that uses analog RGB and separated sync was the target for Philips (or Commodore, in case they ordered the monitors to spec instead of just getting what the manufacturer had to offer). The 8-pin one with TTL levels nicely matches the C128 80 column RGB output. The Amiga which has analog RGB outputs both composite and separated sync, so you can choose which signal to use. That pretty much sums up the market of Commodore branded computers at the time, even if we consider PC models with CGA that equal the C128 here.

 

Philips' own MSX and MSX2 models usually had built in SCART output in the case they did RGB at all. Perhaps some earlier Philips P2000C or similar? VG-5000? Not that it matters, perhaps there simply was a market demand for that at the time, or easier for the monitor to work with a separated sync.

the sad thing is seeing that scart port covered lol... :(

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