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What's currently the best RGB mod for the PC Engine?

Discussion in 'Modding and Hacking - Consoles and Electronics' started by FireAza, Apr 17, 2013.

  1. FireAza

    FireAza Shake! Shake!

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    Yup, it's a PC Engine themed version of the thread I previously posted about the Famicom ;)

    I've got a PC Engine on the way (Obey and all that), and I'll be wanting to RGB mod it. I had originally planned to pick up one of the kits from Retro Accessories, but the guy is sold out and doesn't seem to be answering my messages, so I guess I'll have to do it myself. Reading around, there seems to be a few different ways of RGB modding the PC Engine, but I like the looks of THIS GUIDE over at mmmonkey's site, mostly because using the mini DIN socket makes everything very neat and tidy.

    What's your options on this mod? Does it produce the best results for the PC Engine?
     
  2. ApolloBoy

    ApolloBoy Gutsy Member

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    I wouldn't recommend doing the Mmmonkey mod at all, the RGB outputs have too much voltage and there's nothing in that circuit that'll deal with that excess voltage. I also don't understand why he's using an 8-pin mini-DIN when you can just use a 9-pin mini-DIN (same as the Genesis 2/MD 2). By using the 9-pin mini-DIN you can use any cable meant for the Genesis/MD 2 (no need to build your own) and you also have separate pins for composite video and sync.

    Anyway, here's a circuit which worked out very well on my TG-16, courtesy of micro on NFGGames:

    [​IMG]

    The version I built was very similar, except I substituted the 82 nF caps for 0.1 uF, the 3.6 M ohm resistors for 5.1 M ohm ones, and the 330 uF caps for 220 uF ones. I also omitted the 100 nF cap for the 5V and ground pins of the THS7314 as I thought that the 22 uF cap sufficed.
     
  3. FireAza

    FireAza Shake! Shake!

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    Cool! The 9-pin mini-DIN is the same size as the 8 pin right? No idea why mmmonkey would make the process harder than it needs to be :\

    *EDIT* The Retro-Accessories guy got back to me, he's gonna do up some more PC Engine RGB mod kits. HERE'S HIS KIT, any thoughts on it?

    Also, if you've got the console connected to the Interface Unit, you're still able to use the console's video out instead of the composite video on the Interface Unit right?
     
    Last edited: Apr 19, 2013
  4. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    Its just the mmmonkey amp with transistors already in the scart cable (probably, as it says there is an amp - but its not console side from the pictures)
     
    Last edited: Apr 19, 2013
  5. FireAza

    FireAza Shake! Shake!

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    What's your thoughts on the excess voltage issue ApolloBoy mentioned? Should some extra components be installed if I went the kit route?
     
  6. ApolloBoy

    ApolloBoy Gutsy Member

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    I would just suggest going with the circuit I posted, it's safe to use and it's fairly easy to build if you have SOIC-8 adapters. And again, with this circuit and a 9-pin mini-DIN, there's absolutely no need to buy or build a special SCART cable.
     
  7. FireAza

    FireAza Shake! Shake!

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    I've never even heard of a "SOIC-8 adapter" so I'm worried it might be beyond me :\ Sure, I could solder everything together, given the parts and a simple diagram that shows me what needs to be soldered to what (emphasis on "simple" here ;)). I'm trying to decode the diagram you posted, I can see it involves 3x 330 uF capacitors and a handful of resistors (though I can't make out what value) and what I think are non-polarized capacitors. Are the rectangles with the circle in them the legs of one of the PC Engine's chips? Sorry, I'm no student of electrical engineering, I study design which is pretty much on a completely different planet :p
     
  8. ApolloBoy

    ApolloBoy Gutsy Member

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    A SOIC-8 adapter is a little PCB that allows you to adapt an 8-pin surface-mounted chip for through-hole usage, here's what one looks like:
    [​IMG]
    I use them for THS7314s and they've become essential for me. It makes it much easier to work with the THS7314 since you're not soldering components directly onto the legs with this.

    Anyway, here's the gist of the diagram. For your RGB inputs, you can grab them from either the HuC6260 chip, or even better, you can get them from the expansion port connector (no soldering onto tiny surface-mounted pins this way). From there, your RGB inputs will each pass through a 0.1 uF ceramic cap (micro's schematic calls for 82 nF ones but I was able to substitute them for 0.1 uF caps without any issues) before they go to the respective input pins of the THS. After you've done that, you need to wire 5.1 M ohm resistors to the output ends of the caps and tie the other ends of the resistors together to 5V. The schematic calls for 3.6 M ohm resistors but calpis suggested using 5.1 Ms in another thread here, so that's what I used. That about does it for the input end.

    For the outputs, you can use 220 uF caps instead of 330 uF ones just fine. Each positive lead of the cap goes to the THS's outputs while the negative end of each goes to a 75 ohm resistor. Of course, on the other end of each 75 ohm resistor will be your final output. You'll also need to grab 5V and ground for the THS, but you'll need to add a decoupling cap across the voltage and ground pins to protect the THS. The schematic calls for a 100 nF ceramic cap and a 22 uF cap connected in parallel, but I only added the 22 uF cap as I thought it was enough.

    Hope that clears it up.
     
  9. FireAza

    FireAza Shake! Shake!

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    I *think* understand it a little better... I think what I need is a simplified diagram without the schematic symbols (kinda like what I did HERE) or even better yet, a photo of what the whole thing looks like so I have an idea of what I will be doing. Sorry, it's the designer in me :p Heck, I might even try making one myself and get you to look it over :p

    *EDIT* I've made a roughed up "idiot's diagram", here's what I have so far:
    [​IMG]
    I'm not sure what wires go to what pins on the DIN connector, and I'm not sure where the "VCC" and ground points are on the PC Engine's mainboard though.
     
    Last edited: Apr 20, 2013
  10. drakon

    drakon Gutsy Member

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    The ths7314 amp was first posted I believe by baku for use with the rgb av famicom mod on a japanese blog. Then everyone just used it for all other consoles that need a rgb amp since it works and it's a very simple circuit.

    I agree with apolloboy if you have a genesis 9 pin mini connector just use that. Fireaza your circuit picture is missing the power decoupling caps.
     
    Last edited: Apr 20, 2013
  11. ApolloBoy

    ApolloBoy Gutsy Member

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    You should also attach your component leads and wires to the holes in the SOIC-8 board, not on the legs of the THS itself.

    Ground you can grab from a lot of points so no problem there. The same goes for 5V, you can get it from the output leg of the 7805, pin 38 of the HuCard slot or from the expansion port. Here's a diagram of the Genesis/MD 2 AV pinout:

    [​IMG]
     
    Last edited: Apr 20, 2013
  12. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    the polarised caps are also backwards
     
    Last edited: Apr 20, 2013
  13. FireAza

    FireAza Shake! Shake!

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    "power decoupling caps"? You mean those non-polarized capacitors at the middle bottom of the original diagram? Yeah, I am, but that's because I'm still not entirely clear where the "VCC" part is on the PC Engine... Also, RGB Famicom mod? You can use this circuit to get RGB out of the Famicom??

    Ah, so that's what those holes are for! I'm assuming that you need to solder the wires to the correct holes right? How do you know which is the correct orientation? I'm assuming the square in the corner tells you somehow.

    Also, for the mini-DIN connector, how do you know which pins lead to what socket? Are they numbered or do you just use a multimeter?

    Ah, that's how they were when I copied the image, but yeah, you're right, they're around the wrong way :p

    Here's a slightly updated diagram, I think once it's been made clear where the "VCC" point is (is it something to do with the point where you take 5v from?), I might be able to finish it :D I've also added the wires for the audio, do they need any extra components to be soldered to them, or are the OK going straight from the expansion slot?
    [​IMG]
     
    Last edited: Apr 21, 2013
  14. ApolloBoy

    ApolloBoy Gutsy Member

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    The power decoupling cap is the 22 uF cap going across the 5V and ground pins of the THS7314, not the caps for the outputs. Again, VCC is 5V; VCC is a standard term used to refer to the voltage pin of an IC. You can't use this exact same mod for the Famicom/NES, but there is one that uses the same amplifier chip used here, which is what Drakon was referring to.

    It should be obvious as you can tell by looking at the traces going between the solder pads for the chip and the holes. The square-shaped hole on the particular example I posted is usually used to represent VCC, but there's plenty of SOIC-8 adapters that don't have this.

    Again, just follow the pinout I posted and you shouldn't have any trouble.

    It's fine to take them straight from the expansion port, but it might be a better idea to add 1 uF caps to protect the audio circuitry.
     
  15. FireAza

    FireAza Shake! Shake!

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    Ah, I get it now! It would be nice if they used "5v" or something intuitive like that :p

    Oh, I take it you still need a playchoice 10 PPU either way?


    I think I get you, you need to follow the traces from the THS7314 to the solder points on the adapter to make sure you're soldering the wire to the correct point right? It's tricky to tell this from the photo alone (esspecially since the 3D render I used of the THS7314 doesn't have the notch in it, so I can't tell which way is which!)

    I understand the printout no problem, I was just wondering if the socket itself would have numbers printed on it that would match what's in the printout, or if I would need to break out the multimeter to figure out which pin is which. ;)


    When you say "protect the audio circuitry", do you mean protect from electrical damage or to prevent noise being introduced into the signal?

    Alright, here's an updated diagram, let me know if I've got it right (I'm going on the assumption that the square solder point of the adapter is ground)!
    [​IMG]

    As a matter of curiosity, there's been a few times were you have casually said that you thought it would be better if you replaced components in the circuit with ones of different values. As someone who doesn't know much about electronics, this seems kinda crazy, since I would think changing the value of a component would do something like make the picture brighter/darker. In real basic terms, how are you able to do this without effecting the picture?:eek:
     
    Last edited: Apr 21, 2013
  16. TriMesh

    TriMesh Site Supporter 2013-2016

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    True, but Vcc is one of those conventions that's been around so long that you just have to get used to it. In practice, "Vcc" will normally be +5V, although this wasn't always the case - the first generation Fairchild 900 series chips from the '60s used 3.6V (but still called it "Vcc"):
     
    Last edited: Feb 1, 2014
  17. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    VCC isnt "normally 5v"

    Its what ever the circuit requires. 3.3v, 1.8v, both are common.

    5v tends to be for older stuff
     
    Last edited: Apr 22, 2013
  18. ApolloBoy

    ApolloBoy Gutsy Member

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    Yes.

    Yes.

    It doesn't have numbers, but the pin spacing should clue you in regardless.


    The former.

    That looks OK for the most part, but I assume you won't be using that much wiring in the actual circuit? Ideally your component leads should be placed into the holes of the SOIC-8 adapter, that will reduce the footprint of your circuit and also prevent possible interference from being introduced. The 22 uF cap should also be placed directly into the SOIC-8 adapter, not near the expansion port as you have it.

    It's not all that crazy, changing capacitor values in this case doesn't really affect the original circuit much. One of the reasons why I made substitutions was to reflect the parts that I had on hand as 82 nF isn't as common a value as 0.1 uF is. Another reason for the input cap and resistor value changes was because that was what calpis suggested in another thread about this subject. The resistors on your output would definitely have an effect as anything stronger would weaken and darken your image, and as a result they should be definitely left alone.
     
  19. FireAza

    FireAza Shake! Shake!

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    Yeah, I won't be using near that much wiring (i.e soldering components directly to each other instead of having a wire in between and keeping the remaining wires as short as possible). Do have you have any other tips for keeping it tidy?

    I'm trying to work out what you mean by "The 22 uF cap should also be placed directly into the SOIC-8 adapter" though. My interpretation of your original diagram is that it needs to go between ground and 5v, but the problem is, that's two separate wires. Do you mean something like this:
    [​IMG]
    (in case you can't see it (the legs of the 22uF are thin), the 22uF is connected to both the 5v and ground wires, acting as a bridge between them.


    Hmmmm, I see. I think :p Thanks for the clarification!
     
    Last edited: Apr 22, 2013
  20. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    The cap should be as close to the chip as possible. So solder the cap to hole 1 and 8 on the soic adapter. Do not use wires. You can then solder the wires for VCC and gnd to the same points the caps are already soldered to.

    Imagine something similar to this:

    [​IMG]
     
    Last edited: Apr 22, 2013

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