Composite Sync Stripper LM1881
Here’s how to build a Sync Stripper from the popular LM1881, some TVs or Signal Converters (VGA to RGB scalers etc) work better if the Composite Video signal is cleaned up, the video signal is ripped out, leaving the clean Composite Sync signal.
This is the schematic I used from GamesX
And here is a diagram of the board I made, along with a few photo’s. You can make it small enough so that it fits in a scart plug. The one I made below is obviously on too big a piece of board, I was originally going to mount it in a project box along with some other bits and pieces, but ended up not using it in the end, and making a much smaller one to put into a scart plug, I squashed the components by putting the leg from the capacitor and the chip through the same hole etc.
Here you can see one I managed to squeeze into a scart plug, using scart pin 8 to supply the power. I joined up all the ground pins, connected Red, Green, Blue, Left, Right, 8 and 16 for AV and RGB switching etc from the relevant pins on the scart socket at the other end of the cable.
This one below is the smallest I could make it (on a piece of boaard) to fit into a scart socket plug for a converter I was making.
The LM1881 doesn’t provide a Horizontal Sync Output, you may get away with using the Composite Sync Output instead of it, it really depends on the display device.
I built this for my CGA/EGA/RGB to VGA GBS-8220 upscaler (that’s what the last two photos are from), I just needed the Composite Sync output, and selected the RGBS input on the upscaler. I did try the upscaler without the sync stripper, but when I tried my Saturn it would display a picture for a few seconds, and then vanish.
In addition to the above, I decided to make a really small one not using any circuit board at all (as I got more confident in my soldering skills, and I got fedup cutting up bits of board!). I start by cutting the legs off that aren’t needed, and shortening the other legs, then bending and soldering on the components.
I recently had to build one of these for another GBS-8220 Scaler. Except I ordered LM1881M (instead of N). Turns out it is the smaller surface mount version of the chip. I had already had some practice with the similar Amp that I used on the N64 RGB Mod.
I already had some adapter boards from the same N64 mod, these were from eBay (I searched for SOP DIP8).
The first thing I do, is put a piece of double-sided tape down, and sticking the adapter board to it to stop it moving around.
The dot in the bottom left corner shows where to put leg 1 of the chip. This is linked to the hole in the top left – labelled 1 on my board, but it could be another dot.
For reasons that will become clear later, but I cut the trace that is coming from hole 7 (second one down on the right). I simply put the point of my sharp scalpel on it and twisted it around – effectively drilling a little hole. Not all the way through! Just enough to break the trace.
Now I hold my soldering iron on a pad that the LM1881M chip will attach to, after a second or so I touch some solder onto the pad, you don’t want a lot on there. I move the soldering iron back and forth along the pad to even out the solder and remove any excess.
Here comes the chip now, leg 1 of the chip will be marked in someway, usually with a dot in the corner of the chip where leg 1 is.
I always start by holding it securely in place with some tweezers or by putting some pressure on the top, and then put my soldering iron on a corner leg, this heats up the solder underneath it and then i gently push the leg down into the solder. Try and keep it lined up, but don’t worry if it goes a bit wonky.
I’ve soldered the top right leg, and you can see I didn’t do a great job at keeping it straight – look at the legs going down the left side.
Either heat up the single leg and adjust the chip, or (and this is what I did this time), I turned the adapter board around to make it easier for me to solder, I slightly twisted the chip so it lined up with the pads again and then soldered the opposite corners leg.
Once I was happy it was straight enough, I solder all the legs on one side in place. I use the soldering iron to push the leg into the solder (hold it there for a bit to heat it up), then drag the soldering iron away from the leg and then back to and onto the leg. This is without adding any extra solder to the iron etc.
Fingers crossed, you get a nice clean join between the legs and the pads all around the chip.
I’m not sure if I did the next bit in the correct order to make it easier for myself or not, but I then started with the wires. Black wire for Ground first, this goes to hole 4, count down from hole number 1 which is labelled (depending on your board, it might just be labelled with a white dot)
With all the wires, I stripped a bit from the end, twisted it to keep the strands together and then pushed them through the relevant hole.
Then it’s just a case of heating the wire and the hole before adding some solder. I usually trim the soldered wire a bit shorter after I have soldered it – using side cutters.
Power wire next, this is to leg 8, the opposite corner from Ground.
I forgot to photograph it, but in a moment you’ll see that I soldered a yellow wire (for Composite Sync Out) through hole 1.
The next wire is the Composite Video In wire, I’ve used grey. If you study the diagram at the top of this page, you’ll see that the video in needs to go to leg 2, passing through a capacitor. Remember we cut the trace leading to/from hold 7, this is why. Leg 7 isn’t needed for this to work for us, so we are using hole 7 to solder the video in wire, and then linking hole 7 to hole 2 using the required capacitor.
With the Video in wire in place, turn the board over and bend the legs of the capacitor so that you can solder it in-between legs 7 and 2.
I usually start by leaving one leg uncut, holding it by that leg whilst I solder the other leg in place. Once one leg is soldered, I line up the other leg with the hole, cut the leg to the right length and then solder it.
Nearly there! Time to solder a second capacitor AND the resistor from hole 6 to hole 4 (the one we soldered the ground wire through at the beginning).
Again, I tend to bend and cut one leg to length, solder that in place and then line up/bend, cut and solder the second leg.
A leg from each will fit through hole 6. Once hole 6 is soldered, it’s time for the final part – linking the other legs of the capacitor and resistor to hole 4/ground.
Finally, I decide to insulate the finished board, I cut a piece of heat shrink tubing, insert the board into it and then heat it up. You can always use insulation tape, or, depending on where you are using it – you may not need to insulate it at all.
Ready made Sync Cleaner
It seems a lot of people want this for their VGA Scaler. Well arcadeforge have developed and now sell the Sync Strike, I’ve tried one out and it works brilliantly with the VGA scaler. You can even buy the complete setup, Sync Strike, VGA Scaler and SLG3000 as a kit now, a plug and play kit for playing retro consoles on your HD TV via VGA with an awesome picture. Thanks Jochen :-)
You also have the option of buying a very neatly designed circuit board that fits inside a Scart plug – designed and sold by RetroRGB in America, also sold by Videogameperfection in the UK. So simple, it’s genius.
Summary of Components needed
- 2 x 0.1uf Capacitors
- 1 x 680k Resistor
- 1 x LM1881n chip
- Wires, Veroboard/Stripboard (optional)