Apologies in advance of this long story, I just want to make sure you have all the information to helpfully solve this issue. Here goes:
I am attempting to replace the crappy 27" WG D9200 monitor in my Big Buck Hunter II arcade machine with a 27" Toshiba 27AFX55 TV screen. Before taking the plunge of swapping around the components and doing an RGB mod, I wanted to do a test to make sure I could output the signal from the game board to the tv. Here's how I've set things up for the test:
The TV has component inputs, and I have a RGBs/VGA to Component transcoder (I use this with a SCART cable for my PS1) that can take VGA or SCART inputs.
https://www.amazon.ca/Component-Converter-Genesis-Dreamcast-Supports/dp/B0BLH7FZSRI unhooked the VGA cable from the BBH graphics card that normally goes to the game board and plugged it into this thing, then connected it to the TV with component cables. The result had a few issues:
1. The image had quadrupled and the scan lines were very fat with large black gaps between them. Not a great image at all
2. The light gun and 'Start' button no longer functioned. I think this is because I bypassed the jamma connection by taking the video signal right from the graphics card instead of from the jamma's RGBs output.
I figured maybe this was happening because the game was sending out a 25khz signal, so I turned everything off and using the manual I located the dip switches on the game board that let you switch from standard to medium resolutions. I set it to standard resolution and tried again. I got the same image result.
Thought maybe the video card will always output a higher khz signal and the game board is what does the signal processing to a standard res, so my second attempt would involve using the jamma's RGBs output wires and connecting those to the transcoder through the SCART port. I found pinout diagrams for the scart port, figured out where each R,G,B,S, and ground wire went, rigged up some connections, turned it on and got the same result! However the start button and light gun now worked, so that's a step in the right direction.
I remembered reading that arcade game boards usually have a higher signal voltage than a tv expects. I looked at the schematics for the WG D9200, and at it's video/sync board it shows that the signal coming into it is 2.2Vpp, and the output connection from it is 0.7-1.0Vpp which sounds more like what I want. Looking over this schematic, it has all the resistors necessary to create this voltage drop, so I connected all my wires to that output and ran them back into the scart port and tried again.
This time the image was almost completely black with some very distorted/grainy white illegible text squished into the corner.
About this time I figured I should start measuring the signal voltages to see just what is going on. I don't have an oscilloscope, so I can't read p-p voltages, so I'm just using a normal multimeter.
The RGBs wires coming out of the Jamma show this:
R,G,B = 0.22 - 0.55v
S = 4v
The schematic said these were supposed to be 2.2Vpp, so I was a bit confused by how low those readings were. Do I need to multiply those x2 to get the p-p voltage?
I then plugged that cable into that video/sync board and measured the output and got:
R,G,B = 0.15 - 0.28v
S = 0.79v (i pulled this from a junction after R522 since there was no sync pin at the W506 output to neck board connection)
These readings were even lower, so probably why there was barely any image on the 2nd attempt, but if that's the case how did this thing every work when it was hooked up to the D9200?
Did some reading on Scart wiring for arcades and some people suggest you need to apply 5v blanking signal to pin 16, probably with a 100-150 ohm resistor to reduce the voltage to around 3v. Tried that (without that BBH video/sync board) and still got the same results. Tried again without the resistor at the full 5v and got the same result.
Looking at my test voltage results, I thought maybe the RGB signals are fine and it's just the sync that's too high, so I tired a bunch of various combinations of resistors to try and get that 4v down to around 1v, and it just wouldn't. Lowest I could get it was 2.5v and I still had the same image result. I think the transcoder has some internal resistors that are thwarting my voltage drop attempts.
Maybe something was wrong with the component inputs on the TV? Nope, hooked up an xbox 360 and it looked great!
Maybe something was wrong with the SCART port on that transcoder? Nope, hooked up the PS1 with it's scart cable and it looked great! Since this used the scart port and worked, I wanted to see what the signal voltages were to get this great result, so I popped open the scart connector on the cable and with it exposed and the PS1 running, I tested the pins and got:
RGB = 2.0 - 2.4v
S = 4.5v
Blanking = 5v
These voltages seem so high compared to what the BBH game board was putting out. It's almost like the game isn't sending a strong enough signal...
I came across this post about another BBH machine and it had a very similar looking problem. Turned out to be standard resolution monitor displaying the game at medium resolution.
https://www.reddit.com/r/arcade/comments/zkg2vj/big_buck_hunter_double_image/I thought maybe the dip switches weren't working correctly and the game was still running in medium resolution, so I tested the switches and they have continuity when turned on, and none when turned off, so those appear to be working. Yet I can't help but think this is still running in medium resolution. I tried running it with the dip switches in either position and I still go the same result regardless. Does that mean the game board is busted?
As a final test I hooked up my laptop to this transcoder over VGA cable and it definitely did not give a good result. I expected this since the signal is likely 31khz which the TV most certainly wouldn't understand.
Does this transcoder just get confused with the BBG signals? Should I just build a voltage divider circuit assuming that the game is actually putting out 2.2v signals and do the RGB mod to the TV and hook it up directly without the transcoder to see what happens?
Here's the mod in case you're wondering:
https://sector.sunthar.com/guides/crt-rgb-mod/toshiba-27afx54.htmlI'm so befuddled by this. I thought this was going to be the easy way to fix this machine compared to trying to repair the D9200. I just want to shoot pretend deer....
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Topic: RGB modded TV for Arcade Monitor (Read 2789 times)
