My silkworm at the top half inch or so of the screen it is "curved" making it impossible to read the score, also the picture jumps up and down by a few pixels every second or so. Pit Fighter works perfectly on this setup, however it also suffered from the jumpy screen before I added a 1k resistor to the RGB sync. Is there something wrong with my silkworm board? Using a higher valued resistor may get rid of the jumping, but I can't work out why the top of the screen is distorted.
It sounds like your display is having problems recovering/locking to horizontal sync before the active video starts. Are you using a RGB encoder (to PAL)? Or does this game have a nonstandard sync? Or have nonstandard video levels? Putting a resistor in series with the sync cable will attenuate the signal, if the game puts out a non-TV sync level (which is 0.3Vpp into 75 ohm), this may be why it helped the other game. If the picture jumps up and down multiple pixels every second though, it does sound like there's something wrong with the game.
Not using any sort of encoder, as far as I know the game is standard 60hz sync. Both Pit Fighter and Silkworm were both suffering from the "jumping", the resistor fixed Pit Fighter but for some reason has had no effect on this game. Well this is really strange I've just fired silkworm up and its jumping like MAD. It was only doing it occasionally last night, and I've made no change to the setup. I've taken a photo of the screen. http://imagebin.org/index.php?mode=image&id=14645 As you can see, the very top of the screen doesnt seem to be horizontally synced properly.
Try Silkworm (and Supegun) on another TV, I remember that Silkworm would bend the top part of the screen on certain TVs and not others.
I would, but only 1 of our TV's has SCART so I'm going to put a 10k pot on the sync and hopefully that will get rid of the problem. Thanks
Another question is it a real board or a bootleg? Fired up a bootleg earlier today and had to adjust horizontal hold to get it to be straight.
Mainly the fact it looks like a bootleg. Another thing I forgot to mention is the fact, you should check to see if your board is getting 5V, although a Raiden board I had from years back would require the 5V signal to be 5.5V else it would give massive issues with the screen warping when the screen got bright. Also check that the Video blanking pin on the SCART plug has at least a 100 ohm resistor between it and 5V, although select the SCART channel directly, again I had an issue with an old Sanyo TV that would warp the screen unless the voltage over pin 16 was correct. As a side note I am currently living in central melbourne and have access to at least 4 RGB SCART TVs.
Well it certainly doesnt look like one, and it has Tecmo silkscreened onto the board (which doesnt mean much, I know). It is getting just over 5v on the board, I have a 100 ohm resistor on the blanking pin and a 1k resistor on the sync, soon to be upgraded to a 10k pot to see if that improves things. As soon as I got the video working on the supergun the power supply shit itself so I haven't had much time to play around with it unfortunately.
Well I've got everything up & running again and put the 10k pot on.. Still no improvement with Silkworm, it actually seems as though the sync signal is too weak rather than too strong. Any suggestions would be greatly appreciated Thanks
I doubt it's too weak, arcade monitors generally require higher levels than TVs. Likely this has nothing to do with the signal anyways, it's probably the game or your TV. Is there a series capacitor on the sync signal? Do you know if the PCB work(s/ed) with an arcade monitor?
The only reason I say it may be too weak is that I get a very similar effect if I turn the sync signal of other boards down. I do not have a capacitor on the sync signal, which value would you recommend trying? The PCB has not been tested on an arcade monitor as I do not have one. Thanks Edit: Just found these JROK Sync Cleaner boards, maybe one of these would be worth trying?
Did you put the pot just on the Sync or did you put it between Sync and Ground? Also remember that if the video signals are too strong then that can effect the picture too. Go to test mode and make sure that the colours are clear and not looking the same for the bright colours. I have access to a arcade machine if you do want to test SW on a real monitor.
Try a 220uF or bigger. Maybe, but just trying another TV/monitor should work just as well because it will give a slightly different result.
Jamtex: The pot is between sync and ground. The colours are perfect, I have pots on the RGB lines and have them adjusted correctly. Thanks a lot for your offer, where are you located? Calpis: Will try that, cheers. Should I put it before or after the pot? Also because the sync is negative I assume the sync goes to - and ground goes to +?
Tried putting a 220uF cap on the sync line, for some reason things are now far worse. Theres something strange happening with the colours and it completely loses sync at times, producing a black screen. This is driving me insane. Edit: Just measured the 5v with the board running, its only at 4.83-4.84v, so I think I've found the problem. However its an ATX PSU so I cant adjust it. I tried putting a 10W resistor on the 12v rail to see if putting a higher load on that increased the effeciency of the 5v regulation and it bumped it up slightly to 4.87v. No idea what to do now.. I've also tried another completely different PSU which had the same problem. It seems a PC power supply needs a much bigger load on the 12v rail than a PCB can provide in order to regulate the 5v correctly.
You should first remove the pot. If that doesn't work, put it after the pot. How are you connecting the pot anyways? One end should be the game's sync, the other end should be connected to GND, the wiper should be the output.
Yes thats how its connected. At this stage I'm more concerned about the voltage, I'm hoping if i can get 5.1 or so volts to the board this problem will disappear. I've heard of low voltages causing similar sync problems on other boards.
I've had it with trying to get a decent voltage out of these shitty ATX power supplies. I'm going to order one of these beautiful things: http://www.happcontrols.com/powersupplies/80021000.htm Also got a JROK Sync Cleaner board on the way. I'm sure the problem will be sorted once I have both of these up and running. Thanks a lot for your advice Calpis and Jamtex
