PC Engine RGB Mod

PC Engine RGB Mod

This is out of date now, if/when I get another PC Engine I will try out an RGB mod using the THS7314 Amp, similar to the N64 RGB mod.

Many years ago Saurian from Bordersdown passed on some info on getting RGB from a PC Engine.  It’s taken me a while but I finally bought a PC Engine and have tried out the RGB Mod.

I only have the original White PC Engine, so can’t confirm exactly what’s needed on the many other hardware versions at the moment.  You do need a 4.5mm Gamebit to open up the PC Engine.

Once you have opened the console up, you’ll notice some shielding on the bottom of the motherboard, this is soldered into place and it easy to remove.  The photos below show the 2 different kinds that I’ve seen and the spots marked in red to heat up so you can remove the shielding.

One piece, with 2 spots to removeTwo pieces to remove, more solder spots to remove

There’s 2 areas that you can get the RGB signals from.  The easiest is the Ext Bus solder points and because this guide is for the PC Engine that’s what I’m going to use.  If you are modding a different model without the Ext Bus, then you can get RGB from the Hu6260 chip (or in my case, HuC6260) and audio etc from the existing din socket.

I’ve seen 2 motherboards, both label the Ext Bus pins slightly different, I prefer the one that is labelled A1-A23, B1-B23 and C1-C23, so that’s how I’ve labelled the photo below, you can see what’s what in the table.

Ext Bus pinouts

Signal Ext Bus Hu6260 Scart Plug Pin
Ground A21 4, 18 and 21
Composite Sync C22 44 20
Red A23 49 15
Green B23 47 11
Blue C23 51 7
5v C21 8 (then 75ohm resistor to 16)
Right Audio A1 2
Left Audio C1 6

Now it’s time to prepare the motherboard.  The method that was recommended to me involves removing the RF Unit and placing an 8 pin mini din socket in its place.  To remove the RF Unit, I added a small amount of solder to each of the 3 tabs that are soldered through the board, they are part of the RF Unit casing.  I then heat them up and using a desolder pump I remove as much of the solder as possible.  Once they are as empty as possible, I remove the solder on the 3 contact pins that are supplying the Audio/Video signal to the unit.

Red highlights show the points to desolder

Take your time doing this, and you should be able to remove a lot of the solder.  I couldn’t get all of the solder out of the 3 large points, so I then VERY CAREFULLY levered the RF Unit off.  I placed a flat screwdriver in between the RF Unit and the motherboard, and then whilst heating the solder I twisted the screwdriver.  I can’t stress this enough, you have to be careful not to damage any of the components near the tabs.  PLEASE, Please, please be very careful.  If you know a better way of removing the RF Unit please contact me.

Using a screwdriver to lever the RF unit off.

Once removed you should find it easy to remove the extra solder from the holes, if you can heat it from one side and use the desolder pump on the other side you should be able to remove it all in one suck!

RF Unit removed!

Now, some people add a standard size 8 pin din socket the PC Engine, sometimes this involves mounting it in the case, or making the hole in the case larger.  Saurian recommended fitting a Board Mounted Shielded 8 pin Mini Din socket (it’s actually the same as the controller port).  Once fitted you don’t have to modify the case at all, so it’s very very tidy.

Test fitting :)

 

We have to mount it to the board though, and we can’t use the normal tabs/legs of the mini din socket to do this.  The following is much easier if you have a fibreglass pencil, you need to scrape away the green coating of the board around where the socket will be mounted, to expose the copper which we can solder onto.

Exposed copper

It should only take a couple of minutes with a fibreglass pencil and it leaves a great service to work with.  It’s time to test fit the socket, you can see I’ve bet one of the tabs outwards, this is to go through mounting hole from the old RF Unit.

Bent tabJust checking it lines up with the case

Once you are happy that the socket lines up with the outer casing, take a scalpel and mark around the rear of the socket.  This may sound odd, but you’ll see why in a moment (don’t worry about the edge with the contact pins, you don’t want to damage them!)…

Used a knife to scratch a line around the socket

Because we only have one tab to solder the socket with, it would be better to secure the socket elsewhere also.  Add a bit of solder to the exposed copper next to the line you just scratched in the board.  The scratch will stop the solder spreading, so it will finish adjacent with the socket.  You can see where I added the solder, and test fitting the socket AGAIN to make sure it’s fine.  Test fit the casing to make sure it fits back on okay.

Solder in placeTest fitting the socket

The socket fitted fine, it’s flat on the motherboard.  If you wanted you could super glue it to the motherboard before soldering it into place.  Solder the tab that we bent to fit through the motherboard, and then add some solder to the rear of the socket and then join it to the solder that we put on the motherboard.

Tab soldered in placeRear of socket soldered in place

It’s time to link up the Audio/Video signals to the socket now.  This is the pinout that was supplied to me, I didn’t see any point in changing it!

I started by soldering one wire at a time from the Ext Bus to the Socket (I did them in this order GND – Right – Left – Sync – Blue – Green – Red – 5v, I found it easier to solder the socket this way).  Here’s where I routed the wire, it’s Kynar wire again – a modders friend!

Socket wired up

Time to solder up a Scart Lead now.  You could make the whole scart lead, or, you could do what I’ve been doing recently and pickup an RGB scart lead for another more common console and cut the console plug off of it – leaving you with the Scart plug and some cable coming from it.  You’ll have to open the Scart plug up and make a note of what colour wire is attached to which Scart pin. Remove any capacitors or resistors that might already be on the RGB pins (7, 11, 15), and make sure that there is a wire going pin 8, and that a 75 ohm resistor goes from pin 8 to pin 16 (some scart leads are wired up wrong)

Here’s the pinout for the 8 pin mini din plug (assuming you used the same pinout as me for the socket!), the photo shows the side of the plug that you solder onto.

The following photo shows a couple of things.  First of all, I remembered to put the plug casing onto the cable, and secondly – how much of the cable I stripped back.  Because the individual wires can’t be too long, I split the outer cable so that I could work with the individual wires easier.

Preparing the cablePreparing the cable

To solder the wires to the plug, first of all add some solder to both the backs of the pins and the wires.  The photo above shows how much exposed wire I leave on the wires – it’s not much at all.  I keep it short to help keep the plug tidy.  I usually strip too much wire back so that I can twist it up and then melt solder into it, finally trim it short.

I then put the wire near the contact, heat the contact up and push them together, simple if you prepare them properly and take your time.  I find it easier to start with the very middle contact, then solder one line of contacts at a time, then try and arrange the wires ready to solder the next line (this is why I put a couple of splits in the black cable).  Finally you have the plug soldered up.

Finished soldering

BEFORE you put the plug together, solder the other end of the Scart cable together (I forgot to photograph this bit, but it’s the same as the MD2 lead (update link once migrated), but without the resistors on the RGB wires).

Now, back to the mini din plug, put just the metal part onto the plug, you can now test it all out, you should be able to safely put the partially assembled plug into the socket you’ve wired up.

On my CRT TV the image is a bit dark, on my LCD TV the image isn’t too dark, but my LCD doesn’t like any retro consoles – and with the PC Engine the top of the screen wobbles like it’s out of sync.  If your cable is working then finish putting the plug back together and you’re done!

My mini din plug is slightly too fat for the case, but I fixed this by cutting a tiny bit off of the plug.

If the image is too dark, then you can build a simple amplifier using just 3 transistors.

UPDATE

I just modded another PCE but decided to fit the amp in the console.  The following photo shows how I wired it up on the underside of the motherboard.

Of course, you don’t have to fit a socket for the Scart cable, some people hard wire the Scart cable to the console, you don’t have to make a hole for it – you could squeeze the cable out of the hole for the RF unit or channel switch.

Many many thanks to Saurian for the info in the first place.

Summary of Components

  • 1 x Shielded 8 pin mini din board mount socket
  • 1 x 8 pin mini din plug
  • 1 x Scart plug
  • 1 x 75 ohm resistor
  • Cable to make the scart lead (at least 8 core), or a Scart Lead to sacrifice!
  • Some wire (like Kynar)