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Taito B-system/F1/F2: Video brightness/black level issues

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andynumbers

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On all of my Taito PCBs there's an "issue" (probably by design) where the brightness, a.k.a the black level is way too high compared to other PCBs and game consoles with normal NTSC standard black levels.

This issue is present in (but not limited to)
Nastar Warrior (Rastan Saga 2)
Puzzle Bobble (B-system verson)
Space Invaders DX
Cameltry

To help explain what's going on, when I put these games on a HAS supergun and display on a PVM, I have to turn the brightness settings WAY down. It's not a contrast issue, just the darkest black is way too bright by default.

If anyone else here has one of these PCBs feel free to try running on a supergun to see what I'm talking about.

Is there any way to reduce the brightness of the video before it goes to a monitor? I don't think simple resistors would work because that would reduce contrast or the entire signal strength. It's almost like there's some sort of DC offset in the video that's making it brighter than it needs to be.
 
I don't have one of these PCB in front of me to determine if the Video ground is isolated, but I don't recall any of my F2 hardware having brightness issues when running on a cab (certainly other hardware is guilty of this such as SSV).

Does your Super Gun utilize the Video Ground pin or does it ignore it and just use the common ground?
 
The HAS uses common ground. Which HAS version do you have? I'll be honest, I haven't encountered such issue yet.

"Is there any way to reduce the brightness of the video before it goes to a monitor? I don't think simple resistors would work because that would reduce contrast or the entire signal strength. It's almost like there's some sort of DC offset in the video that's making it brighter than it needs to be."

You could try terminating R,G,B lines with 75R resistors to ground to see if that makes any difference.
 
I've uploaded a video capture of Puzzle Bobble to demonstrate the issue:


Captured using PCB->HAS->Extron SW4 VGA (to process sync)->Extron RGB 109xi (to separate sync)->USB3HDCAP (default settings)

In this video you'll notice the elevated brightness levels at first. However after exiting the system configuration page in game, you'll notice that the brightness levels magically fix themselves at this point. I will go back into the monitor test to demonstrate the correct black levels. Once I exit the test mode, the black levels once again return to their elevated levels.

This leads me to believe this is a software issue, or intentional on Taito's part. I just wish there was some way to patch these games to fix this brightness issue.

FWIW, this phenomenon does not exist in MAME. So that would lead me to believe that the game software is controlling something in the DAC or analog video circuitry on board that cranks up the brightness levels. Looking at the Nastar schematics, it seems that all of these boards use the TC0260DAR for RGB output. @twistedsymphony you recently did that amazing F2 conversion of Gun Frontier. I wonder if you can poke around in the MAME debug for Puzzle Bobble to see what's going on when you exit the test menu. What gets sent down the line to magically fix the black levels?
 
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The game doesn't exhibit this behavior in MAME which would make it difficult to troubleshoot

have you verified if the PCB itself uses a common ground or an isolated video ground? That's the first place I'd start. it's entirely possible that Taito is doing this intentionally but it's only being displayed this way on your setup because you're using a Supergun with a common video ground.
 
I thought I would revisit this issue. Aside from the blown out black levels, the other issue is that the video signal is just not very strong. I have to max out the contrast knob on my Egret II MS9 in order to get a decent picture.

The common factor in all of these boards is the TC0260DAR chip, and they all use a C1815 transistor with a voltage divider consisting of a 470 ohm resistor and a 33 ohm resistor. The R,G,B, and sync signals all go through this circuit.

I wonder, would changing out these resistors and/or transistor possibly improve the signal?

@twistedsymphony since you have a lot of experience with F2 conversions, would you check all your F2 boards with TC0260DAR chips to see if they all use this same circuit? I am wondering if there is an F2 ROM board that may have different values.
 
Here's the schematic from Nastar Warrior. The RGB circuit is the same for every board I have on hand that uses this chip. (Cameltry, Space Invaders DX B-system)
tc0260dar.png
 
Just chiming in to say that this issue occurs on my Thunder Fox PCB which is Taito F1 hardware.

By coincidence I noticed it recently and tested it on multiple superguns with the same output issue of the black levels being too bright.
 
F1 and F2 are the same hardware. F1 is just the all-in-one variant and F2 has a separate game PCB and CPU PCB.

My stuff is in storage at the moment so I'm not sure when I'll be able to verify the values on the hardware
 
I can confirm this behavior on F1/F2, don't think I've seen it on B system. It's very similar to how early Video System games like Rabio Lepus are. They all look fine once I get them in a cab and adjust the monitor to compensate. Honestly that's just part of dealing with arcade stuff, some boards have crazy video levels because you're expected to put them in a cab and adjust the monitor to them.
 
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