GBS VGA Scaler
GBS-8200, GBS-8220, HD 9800 and HD 9820 Add-on
I really wanted to make a plug and play solution for the GBS series RGB to VGA Scaler. Luckily the scaler is usually supplied with some cables – one for the RGB input, and another for 5V in – but if you use the normal power socket on the scaler, then the 5V in cable can be used as a 5V out cable.
Unfortunately you do not receive the connector/cable for the VGA socket(s). After a bit of hunting around, I found that they are JST PHR-12 which have a 2mm pitch.
Ideally, I wanted it to not use a project box and instead have something which meant I wouldn’t have to cut too many holes for the scart socket, cables etc. Then I found this on ebay – a scart pass-thru adapter with A/V phono breakout cables.
Easy to take apart, just four clips to open, then pop it open.
This looks perfect, I unsoldered the wires from the rear of the scart socket, and pulled the breakout cables out of the strain relief so that I could re-use it later on.
I had to find something to make a back panel to slot in where the scart plug was, I planned on mounting the necessary switches and 3.5mm audio socket here. After having a look around the house, I decided to go with a spare DVD case, sturdy enough but nice and easy to cut.
I cut a couple out, just in case I made any mistakes. You could actually use scissors for this, but I opted for a ruler and scalpel. Yours may be different, but the measurements for my one were 43mm x 16mm. When I’m cutting bits like this, I make sure the ruler is covering the bit I want to keep, this way, if the scalpel slips and goes off line, it doesn’t cut or mark the bit you want to keep.
It’s not worthwhile trying to cut all the way through it, cut along it a few times and then bend it to snap it!
I actually cut it a bit larger than needed, and then shaved a slither off so that it is a very tight fit.
Although not necessary, I cut the excess bit of plastic away from the both openings so that the holes were square, this was so that I had flexibility when it came to squeezing the board and switches in.
Combing the DIY SLG and the Sync Stripper
I wanted the SLG to have all the switches, but I wasn’t worried about being able to alter the intensity of the scanlines. I drew up the diagrams below (click each one to see it in full). The chip legs coloured in Red are 5V in, the legs coloured in Black are GND, I get 5V and GND from the power lead that comes with the Scaler.
Hopefully, with the colour coding I’ve used on the diagrams, and using the same colour wires, this next bit should be easy enough to follow (and hopefully I won’t miss any bits out like I did when soldering up my previous SLG). Click each of the images to see them in full. The cut the matrix board down so that it is 9 x 16 holes.
This was the first time I had made this, so I wasn’t sure how much room to leave in-between each of the chips to allow for wires etc. I also tried to squeeze the Capacitor and Resistor coming from the LM1881 (and are linked to GND) onto the same row of holes. I used the legs of each of these to do some of the linking up to GND also.
Test fitting just to check.
Not looking too bad, but to save a bit of room, I trimmed the contacts of the scart socket.
Not all my RGB Scart cables are ones that I made myself, some (such as the GameCube RGB cable) have only some of the normal GND pins actually wired up, so it’s very important to link up all the GND contacts on the back of the Scart socket.
I start by snipping off the contacts that aren’t needed (pins 8, 10, 12, 14, 16, 18 along the top row and pins 1, 3, 19 along the bottom row).
Next I’ve bent over the GND contacts so that I can link them up and not use up a lot of space. These are legs 4, 5, 9, 13, 17, 21.
Add some solder to the GND pins. I had to scratch the contacts with my scalpel to get them accept the solder.
Now I’ve added some legs that had previously been cut off of resistors, alternatively you could strip a bit of wire and use that.
Now I take the strain relief that I saved from earlier, and use my scalpel to enlarge the hole running through it so that I can fit a bunch more wires through it. This was just careful cutting with my scalpel. I squeezed all the cables for both the RGB input and the SLG through the strain relief.
For power, I used a salvaged strain relief, I can’t remember where I got this from, I tend to keep bits like this from things that I’m throwing away. I had to use my scalpel to cut a hole for this to fit through in the casing.
Looking at the photo above, the RGB and GND wires from the scart socket go straight to the connector to the GBS board (using the connector that came with the scaler). Yellow comes from the scart socket, into the LM1881 (via the capacitor), and then the Composite Sync output from the LM1881 goes to the same connector to the GBS scaler).
The power lead, coming from the GBS scaler is wired up to the Power and GND contacts of the chips.
(I actually soldered up the RGB, GND, Sync and Power leads first, so that I could test the the LM1881 was working okay)
Before soldering any wires, I tried to cut them to roughly the correct length by placing it all in one half of the case and checking how long the cable needed to be.
To wire up the SLG part, I turned the board over and soldered directly to the where the relevant legs are soldered to the board.
I had left the tape on the rear panel so that I could mark where to mount the switches and audio socket. The switches I used are sub-miniature on/on toggle switches. I wanted to put the switches as close together as possible, but make sure I left enough room to be able to tighten them up to hold them in place. For me, the centre of the 1st switch was 5mm in, then a 9mm gap in-between the 1st and 2nd, then 2nd and 3rd.
I soldered the wires in place, trying to stick to the colour coding again to make following the diagrams easier.
Soldering the switches in place was interesting! It’s getting quite cramped in the box now, I mounted the panel at the rear of the box and then carefully checked to see how long I needed each wire, trimmed them to length, stripped the ends and then tinned them ready to solder in place.
At this stage, I wasn’t sure if I had done this in the right order! Maybe I should have done the switches before soldering the scart socket?? Anyway, I decided to solder the switches to the top side of the board, directly to the chip legs. Carefully bend the scart socket out the way and add solder to the legs that you need to work with.
I started with the switch that had the longest wires on, once finished I did another test fit in the box and it’s looking good still.
Finally, following the pinout from the supplier that I bought the 3.5m socket from, I wired up the audio pass-thru.
It’s a bit of a tight squeeze, but it fits!
I designed mine so that it sits on top of the casing I had made for my scaler (hence the short wires). I could have bought a casing from ArcadeForge, but I fancied trying to create one myself. (although it ended up looking pretty similar to the one from ArcadeForge anyway). Here’s a CAD file that you could send to a company that cuts Acrylic (I used laser-cutting-ne on eBay), some of the holes aren’t in the exact right place, but it’s acceptable. This is only for the 2 VGA output versions of the GBS scaler – the 8220 and 9820.
This file is only provided for personal use, please do not use it to manufacture a product to compete with the much better fitting ArcadeForge product.
After I finished this, I thought I would try adding 75 Ohm resistors the the RGB Outputs of the Scanline Generator – this makes them a bit weaker/less distracting. The easy way to do this would be to unsolder the RGB wires from the 74HC125, solder the resistors in place and then solder each wire to their own resistor.
I had some SMD 0603 75 Ohm resistors, so thought I’d try these out instead of regular sized resistors (plus, it would save a bit of room, but not strictly necessary).
I started off by desoldering the the green wire from the chip leg. Then, with the resistor in a pair of tweezers, I hold it right next to the chip leg, then heat the solder on the leg and push one end of the resistor into it.
That wasn’t too bad, so I then melt some solder to the pad that the resistor is on.
Then it’s just solder the wire to the pad.
And repeat for the other two.
I had read that the GBS Scalers expect Sync of a certain level, and the LM1881 is too high for it. It’s recommended on this site, which in turn references this site to add a 680 Ohm resistor to the Sync Output of the LM1881 (leg 1).
I didn’t have any SMD resistors for this to do the same method as the RGB resistors above, so dug out a regular metal film resistor and instead of simply removing the Sync Out wire from the LM1881 and having the resistor (I was worried it would make contact with one of the switches), I decided to solder the resistor over the LM1881 chip and back down through a hole, and then solder the Sync Out wire into the adjacent hole and linking them up.
When I made a second one of these, I started by adding the 75 Ohm and 680 Ohm resistors from the beginning. I also didn’t solder every single chip leg, only the ones I needed as I went around. Finally, before cutting the legs off of the resistors and capacitors that are poking through the board, I bent them to link up the necessary points that they needed to go.
Here’s the resistor and capacitor that go between LM1881 leg 6 and GND. I’ve poked them through the same hole in the board as leg 6 to save space.
Instead of cutting the legs off straight away…
I’ve bent them and used them to link up to GND on the relevant legs.
This is the additional 680 Ohm resistor on the Sync output pin on LM1881, it’s not in the diagram above as I read about it being necessary after I drew the diagram. See this site, which in turn references this site for info on why the resistor is necessary.
I poked the second capacitor on the LM1881 through the same hole as the leg it needs to attach to (leg 2), this was to safe space but probably wasn’t necessary.
Cut off legs from resistors and capacitors used to link up the power inputs on the chips.
And adding the 75 Ohm resistors to the scanline outputs, again, the resistors are pushed through the same holes as the chip legs.
Sometimes it was necessary to use some cut wire for links between some of the legs, these are the ones where they would overlap. Where there was no overlapping, I used more cut off bits of resistors/capacitors.
Now it’s ready to solder the switches, input and output wires as per the rest of this guide.