Schem for adding composite video to original PCE

[segasonicfan]

Hey folks,
  first time post here!  I recently acquired an RF-only PCE and I really wanted to restore the original composite functionality without an AV booster.  This wasn't as easy as I thought it would be, since schematics only exist for the RF model of the TG-16 as far as I can tell.

Well a friend of mine let me borrow his core graphics II and I reverse engineered some of the video and audio circuitry. If anyone's interested, I can draw up the schematics to share online here.

–Segasonicfan

[SignOfZeta]

The all Core systems have complete composite video coming from the expansion bus from the factory. All you need is two conductor wire, an RCA jack, and some sort of terminal end. You don't even need to open the machine.

[NightWolve]

Old news my friend, and the stereo channels are also available in the expansion port ready-to-go which is true for all models US/JP. With no mods you could wire something up like this:



http://www.cgquarterly.com/2010/04/26/building-a-turbografx-16-pc-engine-composite-av-cable/

Where we need smart EEs is to perfect tapping the raw RGB and Sync signals for 1) proper amplification for 75 Ohm terminated RGB monitors and 2) YPbPr/Component signal encoding for most US TVs that accept a 240p signal in the Luma/Y RCA input jack, what I have an old thread for thanks to the work so far of Steve Hanley, one of our longtime resident PCE modders/repairmen with a formal EE background.

[segasonicfan]

None of these are the correct way to make the connections. They are missing proper decoupling capacitors and other parts. Yes, it "works" but it is still incorrect (and somewhat unsafe for your television).  The Core Grafx II has these parts coming from the expansion bus and creates a proper AC-level composite and audio video signals in line with proper NTSC standards.

I wanted my original PCE to have a proper output /exactly/ like the Core Grafx II.  Happy to post info for others that might be interested in this.

-Segasonicfan

[segasonicfan]

Not that anyone cares, but I whipped up the correct circuit.  Add these parts for correct A/V out on a white PCE (they are found in the Core Grafx II).



-Segasonicfan

[NightWolve]

Not that anyone cares, but I whipped up the correct circuit.

You never know, somebody could care years from now. It's just that S-Video/YPbPr or RGB signals are so much better and why people are willing to ship their consoles off to the modding pros. I'd rather see the video circuits mastered/perfected for those cases - the public demand/clamor is far more there along with the wishful hope of a feasible HDMI upgrade.

I personally really hated Composite, it was a tad better than RF, but still, once I first switched to S-Video and saw such a contrasting difference, I was bothered by having missed playing games under that quality... Then along came YPbPr/Component which is really beautiful on my 32" Panasonic CRT and is probably the only CRT I'm still keeping (I threw or gave away many others).

Anyway, I'm sure there's something to learn from your circuit and since Steve is floating around lately, he might have a professional opinion to offer about it.

[nopepper]

I originally used the expansion port hack back in the late 90s/early 00s to connect my TG16 and had never heard of it being unsafe or incorrect in any way, so I think you bringing this up is great for the community. So I reckon the turbobooster is more than just some conductors terminating in RCA? I've never owned one, but always assumed that's all they were...

In any case, like NW says, the audience for this will be small, since the majority of peeps that are going to open up and mod (or ask someone else) will go RGB/Component/SVid route.

Still, thanks for sharing.

[SignOfZeta]

None of these are the correct way to make the connections. They are missing proper decoupling capacitors and other parts. Yes, it "works" but it is still incorrect (and somewhat unsafe for your television).  The Core Grafx II has these parts coming from the expansion bus and creates a proper AC-level composite and audio video signals in line with proper NTSC standards.

I wanted my original PCE to have a proper output /exactly/ like the Core Grafx II.  Happy to post info for others that might be interested in this.

-Segasonicfan

So you're saying the CGII has the composite coming from the expansion bus buffered but the OG PCE does not? Doesn't that mean that when the CGII is used in an IFU-30 it will be double buffered and have a dimmer output?

[nopepper]

None of these are the correct way to make the connections. They are missing proper decoupling capacitors and other parts. Yes, it "works" but it is still incorrect (and somewhat unsafe for your television).  The Core Grafx II has these parts coming from the expansion bus and creates a proper AC-level composite and audio video signals in line with proper NTSC standards.

I wanted my original PCE to have a proper output /exactly/ like the Core Grafx II.  Happy to post info for others that might be interested in this.

-Segasonicfan

So you're saying the CGII has the composite coming from the expansion bus buffered but the OG PCE does not? Doesn't that mean that when the CGII is used in an IFU-30 it will be double buffered and have a dimmer output?

Man, that is a good point. I wonder if anybody has compared outputs between the IFU30 and Super CDROM2 with a CGII?

[NightWolve]

As to the circuit, I'm not sure I'm persuaded about how "bad" the raw Composite was out of the external bus pin. I remember it worked well enough when I had a TG-16, but I suppose it's plausible they left the final filter capacitor for the Turbo Booster unit to handle or the CD unit attachments, etc.

Anyway, sounds like he's an electrical engineer, so the more information, more attempts to perfect circuits, the better. I just can't really care much given what I said earlier since focus should be on more advanced component signals (RGB, YPbPr) IMO and one day a feasible HDMI upgrade that can go *in* a Duo versus the boxes (only 2 really) you can buy right now that connect to the external bus of the HuCard-only consoles.