MegaDrive 1 CXA1645 mod

So that really only leaves you with PS1 games played on a PS2 with component? You should consider an XRGB then, there is also the cheaper alternative the HDBOX Pro:
http://www.hdboxpro.com/eng/shop.htm

I don't have any personal experience with that one, and the results will definitely not be as nice as the XRGB-3's, but it's a hell of a lot cheaper.

 

I've got a HD Box Pro (a variant on the name actually but same chipset/hardware inside). It's junk, avoid - it's only slightly better than the scaling hardware in your set is likely to be. If you've only got one set and it only has VGA/DVI then I guess it'd do for PS2 but it's really not a good solution, even with endless tweaking I couldn't get a result that I thought was acceptable.

 

So couldn't someone test this 'scientifically' by going through the variables until we narrow down the actual culprit? Just seems a bit silly to cut Pin 6 and completely disable Composite and S-Video if its unnecessary, especially if the problem could be solved another way? :shrug:

 

Pretty close. That I'm aware, Mega Man X Collection was the sole commercially released Gamecube title in history to output 240p (unless parts of Mega Man Anniversary Collection did?). And no Xbox. Unless I've been horrible mistaken.

 

MegaMan Anniversary runs in 480i on the GameCube

 

Absolutely, it just seems nobody wants to do further testing. If I were doing this myself I'd test for all possibilities before making any irreversible changes.

 

What are we supposed to do? I tried removing the amp, restoring to the original RGB lines and cutting pin 6. I also tried building your simpler amp and it didn't work. If there is a better/simpler solution I'm all for it.

 

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I can't say, I don't have the setup for this. If you're satisfied with what you have now I'd leave it at that. I know for sure that a suitable RGB amp can be built with a transistor, two resistors and no input capacitors, but what I came up with didn't work.

Strange... It's something with the TV, sync is sync is sync so the picture should be in the right place. Is it a HDTV? If so each resolution will have different parameters to center the image and maybe since composite is now irregular (it's luminance) the TV is confused.

Did you measure the pin with a 75 ohm load?

 

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Would this schematic help at all?
http://emudocs.org/Genesis/mega2.png
I dont know if its official or reverse engineered, but it does show the entire video circuit for the CXA1145.

 

That couldn't be properly loaded. From the schematic I guess sync has an open-collector output: (5V / (2200 + 75)) * 75 = 0.165V but that's too low, it should be 0.287V. Like usual there's probably more going on inside the chip...

 

Csync is an open-drain output and needs a pullup resistor. Have a 1K or less instead of 2.2K and lot of problems should get solved.

 

Yes but cutting pin 6 didn't help anything on my MegaDrive. Removing C28 is the same thing so that wouldn't make a difference

 

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Are you sure? Seems kinda hard to think they could make that big of a mistake; 40 IRE for sync is widely universal.

(4.5Vpp / (1100R + 75R)) * 75R = 0.287Vpp

4.5Vpp because the output can't swing all the way to GND, really it's 4.3 to 4.8 depending on load and process.

So I'd use a 1.1K.

Under some circumstances sync doesn't need to be capacitively coupled, but here it should be because the output can't swing down to 0V w/o it. The MD must be assuming the signal is AC coupled at the display input. It also normally doesn't need impedance matching (Zout = 75R) since it's very low frequency; even the 9th harmonic is <200 kHz and that makes a very adequate pulse.

It's a good idea to use the CXA's sync out though because it's probably buffered to the right level and impedance matching which will help with finicky equipment. When you use the proper 75 Rout then you also need the 220uF Cout since they make a suitable RC time-constant.

 

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It's not surprising the CXA output will have a high level like that, the level should be 0.287 * 2, and it probably is with a 2V offset which is removed by the cap. You can't really trust what a multimeter tells you, it's a relatively fast AC signal and the meter will just give you the RMS voltage, not the true Vpp without respect to duty cycle. For that you need a scope.

 

The recommended component layout for XO IN and XO OUT shown in the CXA1145 datasheet does not seem to match the layout Sega used, could this be the cause of the problem? The datasheet shows a 15K resistor to ground on XO OUT but Sega left it unconnected

 

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