Can resistors cancel out each other? SCART question

[Joe Redifer]

OK so I had Retro Console Accessories on eBay make me a cable... DIN 8 to SCART for use in JAMMA. Since Arcade PCBs tend to be overbright, I had her put 75 Ohm resistors on each RGB line. I meant to tell her to put 220 Ohm resistors but that was my mistake. She put 75 Ohm resistors on the DIN side. So I decided to make up the difference by putting 130 Ohm resistors on each RGB line on the SCART side. Now no video at all! I measure resistance pin to pin and I get 129 Ohms. Da hellz? Nothing is shorting anywhere, sync is connected but has no resistors but I don't think it needs any especially since it's going through an 1881 sync stripper chip afterwards. PVM shows a wavy screen (no LM 1881 in that path) and Framemeister shows a perfectly stable pure black screen (1881 on Scart to RGB input).

So my question is... what could cause this? Why does the resistance not add up and why wouldn't I get video. Double checked to make sure they're connected to the right pins on the SCART and everything.

UPDATE: Looks like the sync cable came disconnected on the PVM. Plugged it back in. Got a stable picture, but it is super smeary. Can resistors do that? Well obviously they can but I've never heard of something like this.

[Raijin Z]

I had only the most brief rundown on CRTs when I was in college, so I can't say what would be causing the picture to come out smeared. Resistance values add up when set up in series, like how voltage adds up when you connect batteries in series. Without seeing how the existing resistors are installed, I wouldn't be able to guess if adding more to the output lines would sort it. I'd lean towards replacing the resistors on the input side, since they tend to be the easiest component to work with, and don't break easily.

[xelement5x]

Yeah, I would expect it to act like anything else in series and be a summation of values. Do you get anything with the regular cable at coming out?

I'd guess there is a fair bit of variance with the boards themselves too, do you have the same issue with difference PCBs?

[Joe Redifer]

Well it's not the board (does the same thing on Ghouls n' Ghosts) and I must assume that somehow the resistors are doing this. I'm gonna take off the ones we added today and see how it is (besides too bright).

EDIT: Udate: I removed the resistors and it works, but it's still too damn bright.

[CkRtech]

Hey Joe,

How does your DIN8 to SCART cable interface with your JAMMA connection? Do you have a DIN8 hanging off the loom, or are you using a supergun of sorts?

The RGB signal that outputs from various arcade boards can fluctuate in terms of brightness. Most superguns have a potentiometer so you can adjust resistance on RGB as needed depending on the board you hook up. When I build my supergun and tested it with a Capcom CPS2 board, I wanna say I got well up past the 330 ohm range per color as I was adding/swapping resistors. I might be off on that value - it has been like 6 years - but the important fact here was that I needed a good deal of resistance on RGB in order to get a stable image. I only had the framemeister at the time for testing. As I increased resistance, the resulting image from 0 ohm to 330+ ohm was: Not present -> Dropping out -> Bending/smearing image -> Dropping out on bright screens -> stable.

Rather than go with a cable that has resistors in-line, I would go straight through for your DIN8 to SCART and have some 1k pots for each of the RGB lines prior to the DIN8 connector. You could also do a triple pot for tuning for your colors with a single knob.

[Joe Redifer]

I have a Supergun but it has no electronics inside, just wires, etc. The DIN-8 hooks to that. The potentiometer sound like a good idea. Is there a way to do this so it affects all RGB lines equally at the same time. I'd hate for them to get out of whack with each other.

EDIT: You already answered my Q.