[New revision of my guide] I purchased a pakage with games and a 7800 ProSystem console. It was modified to output C-Video and Audio, in order to get a better quality of both image and sound The work with the new amplifier board has just begun. The C-Video amplifier is located on the left side, while the circuit for the two Audio signals are located ont the top right side on the board. On the subside of the board, there are four rubber feet glued onto it, keeping it away from shorting to the motherboard This is the board itself. Some wires run to different positions of the motherboard, where they are soldered for proper connection A closer look at the connection of the Audio. The wire that runs to POKEY In is soldered to the top of the C14, while the the wire that runs to the Audio In, is soldered to the bottom of the C10 This is the schematics for the circuit. 75 / 82 ohm means that you may choose between 75 or 82 ohms on that resistor. 47k / 68k means that the resistance should be between these values, given that 47k is the lowest and 68k, is the highest value accepted. I picked a 68 komhs resistor, but that is not necessary to do. Pick one that is closer to the 47kohm instead. It is also optional to replace R11 on the motherboard with a new resistor, that is 47 komhs. Doing so will decrease the brightness of the image The cartridge slot is very small, but it's casing could easily be removed temporarely, while soldering the wire to POKEY In, on the top of C14. That way it wont get damaged if the soldering iron gets to close. Once done with that wire, just put back the casing in it's place around the cartridge slot The system is now connected to the new circuit(Note that some wires were exchanged, after I took the picture). I dragged the C-Video In and +5V to the subside of the motherboard and soldered them down there. I choosed to not remove the expansion interface There is a hole in the RF-shield that gives you the opportunity to run out the wires from the inside. That way you wont need to drill a new hole in the shield. It is also possible to solder the GND-wire to the shield, for an easy connection to the GND When the work done to the motherboard is finished, and the RF-shield reassembled, it can be placed back in the casing again. I would rather have the RCA-jacks coming out from the side but it turned out to be very tight down there, so they were placed on the bottom of the top egde instead, at the left side of the console. Solder the wires from the AV-board to the RCA-jacks Once they are on place, reassemble the system. The RCA-jacks goes downwards from the top egde on the left side of the console Then it gets hooked up to the monitor for testing of image quality I started with Galaga. The image looks better in reality, compared with this picture. It is hard to get at good shot from CRT's I took a picture of the the boot up-screen. It looks a little like the one on 5200 SuperSystem, apart from that there is no game title featured on the bootscreen While testing the games included in this purchase, I quickly found a new favourite, Robotron 2084. It was fun to play It feels like a platform version of Asteroids, except that you use two joysticks while playing. One to move around and the other one to shot, in the direction you point the stick. Even the VCS games workd great Hope you all enjoy this guide and that it will come to a better use than the old one
This is an american NTSC version. I dont know if it works for them both. It depends on the outputs where you connect to the video-signal etc. Besides the signal in an PAL 7800 might be stronger or weaker and that decides wheather you should use a certain circuit. This board I built is an amplifier to the signal for the video I guess this mod does not work with PAL systems since the schematics claim it is for the NTSC version
I have two 7800's, one is French (PAL), so RGB output (why I bought it) however other one is stock UK PAL unit so RF only. It will be weeks before I am modding the 7800 but will give your mod a go on my UK unit - if I get no result, should I try a higher or lower ohm resistors on R1, R2 or R3 to experiment?
Good question, I guess I can find out how it is with that and then tell you about it. Otherwise I recommend you to buy an american 7800 and do this mod as some games will not work on a PAL system. Robotron 2084 as an example
...i'm rather hoping the French unit I got is RGB as stated! If that's the case, then by definition the quality of output will be higher than composite anyway.
The french 7800 does have RGB. On the other hand it lacks compatibility to many VCS games from what I heard and then the NTSC games. You should keep the french 7800 but perhaps sell the UK version and replace it with an american so you can play those NTSC games that are unavailable here
i bet a few people at acidmods.com would enjoy this. They really like it when people create pin point diagrams. Pretty impressive mod though. Will you be making it with sound?
It has sound but the audio is not shown in the schematics so I just showed how to do the practical work on the audio when soldering if you look at the pictures that comes before the schematics I might draw new schematics over this mod that looks better and show how to connect the sound
And that's what I did, a couple of years later. I hope that the more detailed guide will serve those who intend to modify their 7800 ProSystem
Nice tutorial and schematic! I designed a board based off your schematic that anyone can have fabricated for their personal use. The board measures 1.00x0.84 inches so its tiny and should fit nicely anywhere. In case anyone wants to build their own with the gerber files I uploaded you can get the materials from tayda which is super cheap. 2n2222 Transistor $0.33 http://www.taydaelectronics.com/2n2222a-2n2222-npn-transistor-0-8a-40v-to-18.html Resistors $0.01 each! http://www.taydaelectronics.com/resistors/1-4w-carbon-film-resistors.html Board costs around $5 for 3 boards ordered from OSHPARK with shipping included.
Helder: That's a damn nice board you manufactured. I will probably buy a few in future, before I make another C-Video modification of the 7800 ProSystem. How much space are there around the corners for the rubber feet? Noticed that they were not mentioned in the guide, so I had to edit that detail in as well
Thanks, but what rubber feet? do you mean something to put underneath the board so it doesn't short something? if that's the case you could just hot glue the soldered resistor legs underneath to insulate them or if you're not afraid of soldering SMD resistors I could redesign the board to incorporate them. Edit: I re-read your post and the dimensions are as follows: The left side of the board from the center of the holes for the resistors to the edge of the board it's 0.4 inches. The right side of the board from the center of the holes for the transistor and resistor to the edge of the board it's 0.3 inches.
Yes there are round rubber feet that prevents the board from shorting. I have never taken any picture of them in man guides. I should do so in future They are good to have as it is flexible to alter something on the board, after it has been finished. The board itself can then also be moved around, upon maintenance inside the console. While being inside, it is placed so that it stays put, but yet flexible, when disassembling the console
