AHA! We have information! (and a possible clue(s) to your problems!--I think)
First of all, the monitor APPEARS to be a Sanyo 20EZ monitor. The part # you got from the tube that starts with 51 is a good clue. (51 = 51 centimeter diameter tube = 20", whereas MOST arcade monitors start with A48 = 48 centimeter=19" tube). Also from your picture, only the Sanyo 20EZ monitor has a strange dual U-shaped braket framing. Most others have solid side pieces followed by a sheet between them, the Sanyo uses 2 brackets that surround the neck (to better protect it) but it's got nothing on the sides.
Here are a couple pictures of the Sanyo monitors.. Take a look and I'm sure you'll be able to tell if it's the same or not:
http://www.dameon.net/BBBB/20ez.htmlhttp://www.arcaderestoration.com/index.asp?OPT=3&DATA=4&CBT=3Okay, to continue this story. You see, about the only MFG that used Sanyo's was Nintendo. EVERY Donkey Kong, Mario Brothers, Playchoice, etc.. that I have seen has always used these monitors. There are two very unique things about them. (Acutally this could be more said of the Nintendo game boards and the monitor they picked happened to deal with it with an inverter board)
1) They use 100 volts AC and NOT 110/115/120 volts. Nintendos, being made in Japan, used a step-down transformer to reduce the voltage to 100 volts on its power boards in the cabinets to both power the flourescent light and the monitor at 100 volts (and the AC->DC switch-mode power supply too of course)
2) The Sanyo monitors use "inverted video" or "negative video". In other words, 0 volts meant "turn on gun" and 5 volts meant "turn off gun" (and anything in between appropiately). ALL other monitors expect "positive video" -- 0 meaning gun off, 5 volts meaning gun on (2.5 volts = half brightness,etc..)
In addition, the Sanyo requires "negative composite sync" signal. While most other monitors support negative or positive sync, composite or separate (vertical separate from horizontal)
Okay. I will assume that first of all, the cabinet already has the 110 to 100 volt ac/ac converter in place powering the monitor (otherwise it wouldn't work at all).
Second, I assume that the game that was in it before you started was not a nintendo game and was not a negative video game. AND that it likely was a 256 color game. (here is where it gets interesting)
That little breadboard hand wired job labeled 7404? It's a simple 6 port HEX inverter. It looks like they are using exactly 3 of the 6 ports (6 wires, 1 in, 1 out for each) plus another 2 wires for ground (lower left) and +5V (upper right).
What this little chippie does is invert a digital signal from 5 volts to 0 volts and from 0 volts to 5 volts. Basically a "NOT" logic circuit. 0 = 1 and 1 = 0. Click here for more info:
http://www.falstaff.demon.co.uk/7400.htmlThe REASON this chip is there is because the game put into your cabinet had a positive RGB output and not a negative one, and they wanted to "flip" the signal on each of the guns (R/G/B) to get a correct output (otherwise white looks black, black looks white, blue looks yellow (green+red) and so on.... [take it out of circuit and put back in the original game board, or play with mame and see the cool negative color image you'll get]
However, the problem is that I think this is a DIGITAL inverter and not an ANALOG inverter. Therefore it's entirely possible that this is the (1st cause) of your problems.
Assuming it was working entirely digital, then at about 2.5 volts, it will switch the signal.. if higher then 2.5 it will output 0, if lower than 2.5 it will output 5.
Therefore in theory, this would allow only 2 levels of color per gun--digitally. 0 or 5. 2^3 = 8 colors. However perhaps the N series works at more discrete levels inverting them (I don't know enough about the inverter myself) and it is somehow allowing 8 bits to pass through on each gun (2^8 = 256 colors), eg. 0 volts, .7 volts, 1.4 volts, 2.1 volts, 2.8 volts, 3.5 volts, 4.2 volts, 4.9 volts.
However, now you want to run a 4096 color game through it.. That requires an additional 4 discrete levels in the signal (or more if it actually is 16 million color but just selects from a "pallette" of 4096 colors. The inverter chip likely isn't handling the discrete analog levels, and instead is converting them to inverted digital ones, (much like sampling an analog audio signal and creating a digital one from it). Without enough sampling bits, it will tend to be choppy, and thus why you MAY be seeing it as if it was dithering to 256 colors.
Okay... Part of the above is "best speculation" on my part. I COULD be wrong but like I said, most 74xx series chips are digital unless otherwise stated at being analog capable. This is where i think the problem is.
<continued>
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Topic: what kind of monitor do I have (Read 4401 times)
