Dreamcast VGA Box to MS8 Monitor

[dmauro]

I am trying to connect my Dreamcast to my Astro City, but I'm having trouble with the sync signals. Here's my setup:
Dreamcast -> VGA Box -> Video Amp (connects h+v for composite sync) -> Jamma -> Nanao MS8 monitor
My PS2 and PC work just fine with this setup, but the Dreamcast doesn't and I figure it must be because the h and v sync are positive (I double checked with my multimeter). I tried inverting the signals with a 74ls04 hex inverter (I drew the +5v it needs from the jamma edge), but it does't seem to be giving me a negative sync signal. I have it connected like this:

The negative signals that come out aren't negative at all, and I get a slight voltage, but it's much weaker than the sync signal going in.

I'm at a loss here. I just want to make this VGA box put out a sync signal my MS8 can deal with. Any ideas?

(note: the Dreamcast has a +5v pin, but it doesn't seem to actually put any voltage out on either that or the +12v pin when the VGA box is connected)

[northerngames]

have a picture of the vga box?

I have a DC running on my nanao MS8

[dmauro]

Here's a thread on Arcade Otaku I started showing how I modded it for 15/31KHz output.

I wrote to the seller of the 7404 chip on eBay and asked him what he thought and he had this to say:

Hmmmm, since I don't know the characteristics of the H&Vsync
signals you're dealing with, I'll have to guess a bit. The 74LS04
specs indicate that the low level input voltage is 0.8v and low
level input current of -0.36 ma. Depending on where the sync
signals originate, they are generally fairly small signals and may
not provide voltage or current to trigger the '04 transistor array.
Generally when dealing with small signals I have always used an
Op Amp to get the necessary input sensitivity. The 7404 is a
great digital inverter, but I'm not sure that it will handle low
level analog signals very well. I doubt that the IC is bad, but you
can test easily by applying a gnd on an input pin and verifying
+5 on the output and then applying +5 on the input pin and
verifying a low (not quite ground) on the output. General
purpose Op Amps are easy to come by (741, etc) and not
difficult to implement. Hope this helps.

I'm not sure about the amperage, but the sync signals from the box seem to be about +3v.

[northerngames]

I had sold mine and use the arcadecabinets.uk version now but I dont recall using a dark blue wire and believe it was a white wire and it has the #6 painted right on the circuit board and I had suggested clipping the white wire on pin #6 to others in my tutorial and they too got theirs working like mine with no problem so perhaps who ever made that tutorial is wrong on the wire coloring and has the wrong end of the box pin # wise try soldering your blue wire back in and try clipping the white #6 wire instead 

[dmauro]

Sorry for the confusion, that's actually a tutorial I made. I was just linking so you could see what my VGA box looks like. It works fine on my tri-sync monitor, but my low res monitor can't handle the sync signal (I believe because it's negative). What is the arcadecabinets.uk version? Is that a VGA box that puts out a negative sync signal by default?

[northerngames]

 I am not sure but it works great on my nanao MS8-26SU and it also has a built in video amp so the picture is not dull looking.

 I used that box though and pretty sure it was the white wire and the dark blue is the 31k try reconnecting it and clip the white wire instead.

 It may be forced in vga and running vga fine on your tri-sync but your after the 15K so it need to be the other way around perhaps.

 I did have mine going fine but had sold it like a year or two ago and bought the other one otherwise I would post pics of it to be sure.

 Also make sure you have the switch on the hais vga box set in the right position. 

 I have it wired to a DB-9 cable that runs to a DB-9 Switchbox and the same with the pc signals so all I need to do to swap from PC, DC or any other console I just turn the knob on the switch box and their good to go video wise.

 For the controls I have the arcade buttons and joys on DB-25 cable's for wiring from each arcade player and they too go to a DB-25 box so I can swap the controls for PC DC and other consoe's.

 This way there is no tools needed or time involved on what wire goes where and having to tear the machine or CP apart each time it needs to switch it over to another.

 It is alot of work to do at the start with wiring them that way but now there is no work to swap out anything in the end and if so it can be plug/unplug and also be on teir own seperate paths completely.

 The best display for a dreamcast is 15K over any other and it does make a huge difference in display quality over others it is pretty much a sega naomi board but in a home console so 90%+ of the games made were desighned for 15K arcade and also why alot of the games are just like the arcade virtua tennis, 18 wheeler, sega marine, marvel vs capcom 2 etc. 

[dmauro]

I've definitely worked the wires out properly. It switches between 15 and 31 with no problem. Can you post a picture of your VGA box, or a link to it? It's also possible that your monitor can handle the same signal while mine cannot. I believe mine is a MS8-29FSG.

[northerngames]

O yours is a 29" tube then?

I dont have it on jamma so I am not sure about that part part at all.

if your is a 29" that could be it also as the chassis is totally different then mine and just dont like it.

do you have it running composite or seperate sync mine is composite?

I dont have the prior hais vga box anymore only the arcadecabinets.co.uk version and their site is no longer up for some reason.

I can try to see if I can find any of my old post with the hais I use to have.

try the DC straight up with the vga box on a pc monitor and if you get a display then it is not set right if you dont get a display and a out of sync or no signal display then it should be set right but it should not display anything on a pc monitor if it is in the right mode.

[dmauro]

Yeah it syncs fine on other monitors. Just the low res isn't liking it. It is running separate sync, but I'm running it through a video amp for the low res monitor and that joins the sync signals together into composite.

I think the problem with the 7404 is that I was attempting to intercept the sync signals before they went through the 244 which sets them at the proper level, so I'm going to try with the 7404 again, but this time I will use it on the signal after it has fully passed through the VGA box. Hopefully that will give the desired result.

[northerngames]

if it is set for 15K on a stock pc monitor and it is displaying then the box is not set right as you should get no display at all on a regular pc monitor being fed 15K from the DC.

This was pulled form the homepage game consoles link

Dreamcast to Arcade Monitor
  There is a simpler alternative for hacking a Dreamcast to an arcade monitor (other than the RGB/SCART method above). Its possible to hack a Dreamcast VGA Box to output at 15khz.  If you studied the Dreamcast AV pinout you will notice a similar "jumper" method (to that of the Xbox) is used for setting the sync rate. If pin 6 (or both 6 and 7) are grounded the VGA box outputs a 31.5Khz VGA/RGB signal. But if ONLY pin 7 is grounded, the box will output a 15khz signal. So all you have to do is disconnect pin 6 (so it never touches ground). To do this, open up the VGA box, and cut the pin 6 wire where it connects to the VGA box pcb. [You can optionally install a toggle switch if you still want it to function as normal VGA box. You should also use a Multimeter on the Continuity Test setting to trace pin 6 from the DC connector end to where is meets the VGA Box pcb. Also make sure when you cut the wire at the PCB, to leave enough room to re-splice the wire back together if you cut the wrong one -- which is a common mistake by looking at the pinout of the cable backwards.] All that's left is cutting a 9-pin VGA monitor cable (VGA pin out here) to splice the r/g/b/h/v/gnd to your arcade monitor. If you are using a Jamma connector (which only has a connection for composite sync), then twist the Hor and Vert sync lines together and connect it to the composite sync on the Jamma connector.

[dmauro]

Well, the 15KHz of course doesn't work on a normal PC monitor, but I'm testing it on a tri-sync which can display the 15KHz signal. It's easy enough to distinguish between 15 and 31khz signals, so I'm not mistaking it. That bit that you quoted isn't entirely true because it doesn't account for the fact that the VGA box might be using a positive sync signal and that the monitor might not accept it.

[northerngames]

check your monitors chassis make and model and see what all it handles display wise.

looky here maybe this is it hopefully
http://www.twobits.com/sync.html

you have them seperate when perhaps they need to be twisted for composite where there is only one line in and one line out.

it is kinda clicking though becuase my nanao will no do a seperate sync at all for anything I threw at it.

The DC also runs composite sync fine but I am not sure if it will do seperate sync's or not as my monitor canot handle them but I also know that the light guns for the DC work great with composite.

[dmauro]

I'll look up the exact model, but it's a stock Astro City monitor, and it definitely only accepts composite sync, but my video amp puts the two syncs together to make composite.

[northerngames]

did you see where it goes in and out composite on the chip link provided where in your chip pic posted it is seperated and not passing through the chip in composite that way?

[northerngames]

you get it figured out yet?