Build Your Own Arcade Controls Forum
Main => Main Forum => Topic started by: 8way on September 16, 2011, 08:41:13 am
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So i purchased a VGA cable similar to this one http://www.amazon.com/Wii-PS3-VGA-HD.../dp/B0015MISAG (http://www.amazon.com/Wii-PS3-VGA-HD.../dp/B0015MISAG) and im pretty disappointed. The colors are washed out and the whites are blown out. I was expecting a good picture not perfect but ok for the price. So i stated thinking, maybe i can make it better! After some digging, i found that adding some 220uf capacitors to the RGB lines fixed the blown out whites. But the washed out colors still remain. So im thinking, this cable is using a LMH1251 chip and maybe if i add a video buffer(LMH6739) it might improve the picture. Ok so my problem is im very new to electronics, especially when it comes to reading schematics. So i was hoping someone here could please explain in simple terms how and what i need to connect this LMH6739 to this LMH1251. I highlighted the part in question. This is basically for experimenting and learning, in the end i will get a better solution. Any help would be greatly appreciated.
LMH1251
(http://i52.tinypic.com/2ynlzbl.png)
LMH6739
(http://i54.tinypic.com/348le9w.png)
Thanks!
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Anyone who uses an LMH1251 to drive a 75ohm input directly is an idiot. If they're DC coupling it, doubly so. The datasheet specifically says not to do it, and the outputs aren't designed for it in any way, shape, or form.
There should indeed be a buffer between the 1251 and your monitor input. The LMH6739 identified in the datasheet is presumably suitable. The non-inverting input (+) is what you want to hook the outputs of the LMH1251 up to (via those caps, resistors, and clamping diodes - that all builds a DC restoration circuit). The inverting (-) input can be left unconnected since the LMH6739 has internal feedback resistors. Tie the disables high (inactive), and apply a clean power supply between Vs+ and Vs-. Outputs then go to your monitor via the 75 ohm resistors (which is the back termination for the monitor input).
If you're new to things like this, I'd try a simpler project first since high bandwidth op-amps can be tricky to work with. Most of them are only available in surface mount, and they'll tend to oscillate if you're not careful with the layout due to the parasitics introduced. You can certainly give it a shot, though. National will probably sample you an LMH6739 or two for free (they'll even pay the shipping).
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Thanks for the info, but is their anyway you can maybe draw me up a simple diagram on what you just said, cause you lost me. :'(
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Not trying to sound rude but I suggest you hit up Google and researchingch the things MonMotha just talked about. He is damned useful and you'll want to pick his brain with intelligent q uestions.
It's because of his brain that made me realize I completely designed a circuit wrong because I didn't understand what was needed. A post by MonMotha, and a few hours worth of Googling plus a couple of intelligent questions later, I corrected the defect.