Build Your Own Arcade Controls Forum

Arcade Collecting => Miscellaneous Arcade Talk => Topic started by: phillymadison on November 06, 2006, 11:11:29 pm

Title: Dark Screened Jamma PCB Any Help?
Post by: phillymadison on November 06, 2006, 11:11:29 pm

Hi, I just got a jamma pcb in the mail "Street Smart"

I plugged it into my Jamma cab it booted up and its fully playable but the screen is kind of dark

I have a bunch of other boards that work fine in my cab so its not the monitor

any ideas and help would be greatly appreciated

thanks

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: grantspain on November 07, 2006, 02:20:16 am

sometimes you will need to adjust the brightness and contrast when you change boards,its just you have been lucky so far with the ones you have.
some boards will have a slightly lower/higher signal from the r,g,b

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: fredster on November 07, 2006, 02:24:50 pm

You can see if you are getting a video signal by taking the monitor connector off and setting a multimeter to DCV

Put the ground probe in the ground and then test the Red, Green, Blue. If it's dead, then you can trace for a wire short.  If the wire checks out, you can check the board to make sure, but you have likely lost the video chip on that board.

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: fredster on November 07, 2006, 02:45:22 pm

I re-read your original post and you do have a signal.

Two more tips. 

If you find that you are getting a signal from the board, but no video, you can add a ground to the ground on the video cable from the board.  Solder a piece of wire from one of the ground connections to the video ground and then plug in the jamma cable. Some of these cheap asian boards need that in order to work.

(you can just stick one in to see if it helps)

You need to check the sync cable too.  Make sure it's good. Check using your ohm meter or continuity tester.  Make sure it has a really good connection.

Particularly the ground wires.

Adjust the monitor too. Make sure the monitor is warmed up and then play with the "screen" pot on the flyback and if you have one of the sub boards play with "contrast".

I wouldn't recommend turing up the B+ until you have tried all that.  Is this monitor normally dark?

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: grantspain on November 07, 2006, 03:13:44 pm

what have you been smoking fredster ;) the guy said his picture is a little dark,i have seen bootleg boards do this because they require higher than normal +5volts to power all the crappy cheap components and extra board layers but never a problem with wiring or sinc

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: fredster on November 07, 2006, 04:46:45 pm

I got some of those asian boards that needed a boost.  I asked about it to the vendor and he told me to double ground the video ground.

It worked perfectly with them.  I just soldered a jumper wire from the ground at the end of the board to the video ground under the harness. 

The symptom was dark screen with some hum bars.  After the ground fix it was bright and shiny :)

Title: Re: Dark Screened Jamma PCB Any Help?
Post by: phillymadison on November 08, 2006, 12:19:07 am

Thanks guys ill give all your ideas a try  :)