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Newbie trying to run Knights of the Round

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Yoshin222

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I'd like to preface this by saying I am an absolute noob, truth be told up until like, 4 days ago, I had never seen an arcade PCB in the flesh, but the CPS1 has been a point of fixation for me for the past year or so (been looking into reverse engineering/making tools for it) but anyway
Recently, I bit the bullet and got a Supergun, SLG 260 i believe, and a Knights of the Round PCB
The seller displayed the board in action so I'm confident it isn't a problem with that, my running theory is the Scart to RCA converter I'm using, but please feel free to correct me. In the process of tinkering, I have 2 questions
1) I know a lot of things can go wrong with CPS1 Boards, how would one diagnose them? Like, how can ya properly tell the JAMMA is connected correctly, the C Board Battery died, the usual suspects. I'm sorry if these are daft questions
2) Is there anything glaringly wrong with this setup? I know connecting the PCB directly the the Supergun isn't ideal but I can't seem to find a cable for that, and I swear the converter said Scart to RCA! (The red cable isn't connected cause that port on the telly has claimed a few leads as it is!)

Any help would be sincerely appreciated, thank you
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Do you get sound? Superguns mostly output RGB signal, so you would need a converter that would take the RGB signal from the supergun and converts into composite which then you can plug into your TV. Other option offcourse is to get a RGB monitor and plug the scart cable directly into, I think in UK there are alot of consumer grade TVs which have scart input. If you cannot find a TV with RGB input you can get yourself a scaler and then output the signal to a modren display with HDMI. Insert some credits and press start on your controller and see if you get any audio that way would have some idea that your board is alive.
 
My best guess is your Scart to Composite 'converter' is not a converter at all, it's just an adapter. That would mean it is expecting a composite signal coming into the composite pins on the scart connector, which is not what an arcade board outputs. If you have a multimeter you can confirm.

The arcade board is sending RGBS, not a composite signal, so you're not looking for Scart->Composite adapter, you're looking for an RGB Scart -> Composite transcoder.

I don't use these so I don't know what to recommend to you, I'm just linking two that I found so you can see the difference

https://www.ebay.com/itm/174285032048 - cheap, just passing through the expected composite signal
https://www.ebay.com/itm/174578156353 - more expensive, has circuitry to convert from an RGBS Signal to Composite (also it looks like it requires power).

You can see below that Scart can handle separate RGBS Signals on separate pins, or just use pins 17-20 for passing through a composite signal.

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Hopefully someone here has a better recommendation for a RGBS Scart->Composite solution, but that's where I think it's failing right now. Or if you can find a TV that accepts RGBS you can just connect Scart->Scart on that.
 
Ooh these are solid answers, will absolutely chase these up, cheers lads!
I am absolutely a stickler for composite. I honestly adore the way dithering and the like blends on it, really makes the pixel art sing imo!
Oh one thing if it's no trouble, what does that switch near the power lights even do? I can't seem to find a reference to it anywhere and with the output stuff I have no idea what it's actually doing if anything. It has no perceivable effect far as I can tell
 
Yoshin222 said:
I am absolutely a stickler for composite. I honestly adore the way dithering and the like blends on it, really makes the pixel art sing imo!
Click to expand...
obviously it's your opinion and choice to run arcade pcbs through a composite transcoder and play them that way, but I would be remiss to not point out that all arcades running this board would have been using RGBS, not composite. So if you get it running and wonder why it doesn't look like it did back in the arcades, that's why.
 
Have you checked the back of your TV, most uk televisions of that era had a scart socket, if you want to run arcade boards you need one.

As above that scart to phono adaptor you have will not work.
 
Good news, got sound working, good sign!
I'm really married to composite video, what would be the best way to go about that, if at all possible? Again sorry if this is an obvious question
 
Ok tried a few things to mixed results
Bought a converter like the one suggested, but connecting the 3 cables alongside SCART didn't work, and strangely connecting the cable to the converter but NOT to the telly led to the sprite layer being visible, but only as weird white outlines!
Connected the Supergun via SCART, and sprites rendered fine, but nothing else did. I feel like I'm so close but am still missing something, any ideas?
Edit: nevermind, SCART seems to work! Only snag is SCR layers seem a touch finnicky. Not unplayable or anything, it's like they need a second to load in when the PCB powers on and sometimes loading between levels, but otherwise, works fine! But just for my own peace of mind, how would I diagnose how that's happening? What could cause it?
 
Last edited:
Yoshin222 said:
Ok tried a few things to mixed results
Bought a converter like the one suggested, but connecting the 3 cables alongside SCART didn't work, and strangely connecting the cable to the converter but NOT to the telly led to the sprite layer being visible, but only as weird white outlines!
Connected the Supergun via SCART, and sprites rendered fine, but nothing else did. I feel like I'm so close but am still missing something, any ideas?
Click to expand...
Sounds like you have at least two issues:
  1. Get supergun video to display on your TV
  2. Backgrounds aren't rendering

Issue 1 is solved by using SCART. Stick with this for now until you solve issue 2, then you can figure out how to convert to composite (perhaps smear Vaseline on your TV).

For issue 2:
Even if the board worked right before shipping, it could have been damaged in shipping (e.g. blunt trauma or static electricity). Where did you buy the board? Was it a private seller, or a marketplace with a return policy like Ebay? If there's something wrong with the board, and you're bound by a return window, you need to figure out whether you're returning this or not.

The A-board custom chip, CPS-A-01, is often the culprit. The easiest way to diagnose these is to swap boards with a working CPS1 stack, but that's not an option if you don't have it. There isn't a good supply of these available, so if this is the issue, the fix is really to return the board to the seller and buy another.

But you might as well inspect your board for more obvious faults:
  • Corrosion (may indicate a severed trace)
  • Through-hole pins touching on the back side of the board, or some conductive junk bridging pins (I ran into this recently)
 
did you check the 5V pin on the JAMMA connector with the PCB connected and powered up ? you should read 5V. below it that may cause you PCB to act up.
 
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