DL NTSC Decoder on a 4900... powa'?

Scucci

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From what I've been able to dig around and find out... it looks like the NTSC decoder for the 4900 requires +15VDC and a GND... I've been told they have to be from the same source as the monitor chassis... ... read as "powered from the monitor chassis".

How?

I tacked in 12VDC and I ended up with a psychedelic Dragon's Lair screen when red and blue flashing like you would see if a damned Jefferson Airplane video. I adjusted everything on the NTSC card and nothing really improved it. I can only assume it was a power issue... no idea.

Either way, I don't really plan on having a switching supply in the cabinet just to feed +15VDC. So... what's the deal? Where does the NTSC card get it powa' from?

... and what's the deal with the damned trip down the rabbit hole?
 
You are in luck. Many years ago we had a 4900 in a Midway laser disc game. I marked where the NTSC decoder board picked up it's power in my 4900 series manual.

Very simple + and - power leads connect directly to electrolytic capacitor C701 on the 4900 main board.

Decoder + power goes to C701's + terminal and decoder - power goes to C701's - terminal.

It's that easy!
 
You are in luck. Many years ago we had a 4900 in a Midway laser disc game. I marked where the NTSC decoder board picked up it's power in my 4900 series manual.

Very simple + and - power leads connect directly to electrolytic capacitor C701 on the 4900 main board.

Decoder + power goes to C701's + terminal and decoder - power goes to C701's - terminal.

It's that easy!


Nothing needs to be done about blanking or anything like that or is it being fed from the chassis enough to keep the screen from looking like a bad flashback?

By the way, thank you! I'll get those wires tacked in there and see what that gets me. :)
 
From all I can remember from way back then, the NTSC decoder board was made by Wells-Gardner for use with the 4900 series monitors.

The NTSC board had RCA video input jacks on it and a short video output cable with the usual arcade video/sync connector on the end. It plugged directly into the video/sync input Molex on the 4900 monitor just like any old gameboard would have.

The only hardwiring done was the + and - power wires were tack soldered across the + and - terminals of C701 by the Wells-Gardner factory.
 
Which NTSC card are you using? Dragon's Lair used 2 different NTSC cards depending on if you had a Well Gardner or an Eletrohome monitor. The Wells Gardner is square and the Electrohome is rectangular in shape. I think the WG use's 12 volts and you must have a Blanking Input from the monitor chasse to make it work. The Electrohome use's 15 volts and doesn't need the Blanking Input and will work on any RGB standard resolution monitor. In my Dragon's Lair I used a Wells Gardner 19K7901 with an Electrohome NTSC card and I powered it with a 15 volt wall transformer power supply I got from Radio Shack and it worked great. Theirs pictures on my web site.
http://members.cox.net/severlander/Sams_Dragons_Lair_project.html
monitorntsc_426x370.JPG

powersupply_387x339.JPG
 
Which NTSC card are you using? Dragon's Lair used 2 different NTSC cards depending on if you had a Well Gardner or an Eletrohome monitor. The Wells Gardner is square and the Electrohome is rectangular in shape. I think the WG use's 12 volts and you must have a Blanking Input from the monitor chasse to make it work. The Electrohome use's 15 volts and doesn't need the Blanking Input and will work on any RGB standard resolution monitor. In my Dragon's Lair I used a Wells Gardner 19K7901 with an Electrohome NTSC card and I powered it with a 15 volt wall transformer power supply I got from Radio Shack and it worked great. Theirs pictures on my web site.
http://members.cox.net/severlander/Sams_Dragons_Lair_project.html
monitorntsc_426x370.JPG

powersupply_387x339.JPG

I have the WellsGardner NTSC card. The little one that sits on the left side of the chassis.
 
Then from everything I have read you need the blinking input signal and I don't think all monitors have it but you can make a little circuit that will get it working. If you search the Dragon's Lair Project archives you will find it.
 
Hooked it up to C701, getting steady 15V, still having the color issues though.

It LOOKS like the monitor is just degaussing itself, but it's not. And I REALLY hate to put up a video because people won't read this, and will just say "do a cap kit" or "degauss". But whatever... I'll get a video of it. And for the record... the monitor is fine (color wise) with the other games that were in it before I converted it back. And the degaussing coil isn't even plugged it... so, don't bother with that. I can turn the color down all the way on the NTSC card and it's a steady sepia tone, no rainbow effects. I've tried everything on the card that I can think of, but I just can't get the color to be stable.

Uploading the video now...



Edit: FWIW, this is the original monitor for the game. I've checked everywhere on the chassis and I don't see where the op I got it from removed the original wires. Looking at some other pictures I can see there are more wires going to the NTSC card than what I have (2x +15 and a GND).
wells.jpg
 
Last edited:
I found this on the DLP, one of my old posts. WG NTSC has 2 different cards so I don't know if this info is for booth but it suppose to be for the WG P600 board and the WG 4900
From the DL arcives 7/6/2006
No matter what you do it wont work unless you have the blaking signal and you can only get it from the Well Gardner 4900 monitor. You don't put voltage on the blanking signal, don't know if it will hurt it or not but it doesn't work that way. Do a search on this message board and you will see many other people trying to get this card working. A lot of people just use a TV with a video input hooked up to the laser disc player and forget about using the arcade monitor.
Pasted from old post SA Lives - Thanks to Scott Saylor - 4900 NTSC info
The info to use a newer WG NTSC card to a 4900 monitor is as follows:

P-204 connector.
pin 2-goes to j18 (jumper), near c15 in the center of the board. (on the monitor board)
NOTE- you must have r256 (33ohm 1/2 watt) installed on the p600
to lower the voltage to 12v.
pin 3-to ground.
pin 5-goes to r302 on the side that leads into pin 8 of IC301 for
blanking signal. (On the monitor board)
At least thats how I wire them.
Hope this clears it up
 
I found this on the DLP, one of my old posts. WG NTSC has 2 different cards so I don't know if this info is for booth but it suppose to be for the WG P600 board and the WG 4900
From the DL arcives 7/6/2006
No matter what you do it wont work unless you have the blaking signal and you can only get it from the Well Gardner 4900 monitor. You don't put voltage on the blanking signal, don't know if it will hurt it or not but it doesn't work that way. Do a search on this message board and you will see many other people trying to get this card working. A lot of people just use a TV with a video input hooked up to the laser disc player and forget about using the arcade monitor.
Pasted from old post SA Lives - Thanks to Scott Saylor - 4900 NTSC info
The info to use a newer WG NTSC card to a 4900 monitor is as follows:

P-204 connector.
pin 2-goes to j18 (jumper), near c15 in the center of the board. (on the monitor board)
NOTE- you must have r256 (33ohm 1/2 watt) installed on the p600
to lower the voltage to 12v.
pin 3-to ground.
pin 5-goes to r302 on the side that leads into pin 8 of IC301 for
blanking signal. (On the monitor board)
At least thats how I wire them.
Hope this clears it up



... if you two are ever in Nashville, I owe you a 6 pack each. That's for sure.

She's stable. R302 did the trick as far as getting the game off of acid.

Now, I still have to make another connector for those pins, but atleast I know how many, what they're for, and where they go.

 
... if you two are ever in Nashville, I owe you a 6 pack each. That's for sure.

She's stable. R302 did the trick as far as getting the game off of acid.

Now, I still have to make another connector for those pins, but atleast I know how many, what they're for, and where they go.


Thats great, glad to help anytime I can as so many have helped me in the past too.
Now play some Dragon's Lair :D
 
Thats great, glad to help anytime I can as so many have helped me in the past too.
Now play some Dragon's Lair :D

... can't. lol I'm still missing the cable that runs from the game PCB to the LD player. lol But I can watch it now... ... can't listen to it either as I'm missing the audio section of the cabinet... all I really get now is just static with the game audio playing VERY quietly in the back ground.

But, it's running now. So... yay that. I just have to build the other stuff back up because the guy that had it before me gutted it down to the last transformer to convert it to a Trivia Whiz, then to a SFII.
 
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