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View Full Version : Rodotron / Pentranic Help - RGB Input



Berty
7th July 2008, 05:07 PM
I have a Pentranic / Rodotron chassis that it currently being used on a 33" screen. It is very similrl to the one in this picture....

http://www.jomac.net.au/Pentranic_Rodotron_CH288.jpg

(Sorry Joey, had to steel the link cause my camera was dead :redface


They usually have a small "Daughter board" on the flyback side that handles RGB, H Sync and V Sync... but for some unknown reason, this one has been cut off but the RGB, Video Ground and sync wires are still soldered onto the bottom of the board.

I have wired RGB and video ground to these wires, plus composite sync to the H sync wire (V sync is not connected) but i get no image on screen.

The neck is glowing but i cannot seem to get anything out of the machine. Am i missing something? does that daughter board need to be there? I cannot seem to find any other way to "pump" signal into this chassis.

steve2000
7th July 2008, 06:01 PM
I just got one of them chassis for a 26" and it has a place for an inline plug on the main board for the rgb and sync. It is near where the 3 colour pots are.

Berty
7th July 2008, 06:08 PM
Thanks Steve, also tried those too but it was a no-go, I might try and solder one of those smaller boards on and see what happens.

Jomac
7th July 2008, 07:28 PM
Thought that picture looked familiar :)

That little addon board was for 33" tubes only , it's an RGB amplifier needed because these chassis didn't drive the color input properly.
If you touch 5 volts from the power supply to either of the RGB inputs you will see if the chassis is working properly .
If you see the color you connect the 5v to go flatout on the screen it means you need that little amp.

V Sync is never used on these chassis , but you need - Comp Sync , if this is not connected it puts the screen in standby ( black screen) , you will know when the sync is connected properly when you touch the 5V to one of the colors, if you still get nothing there is sync issue .

Berty
7th July 2008, 08:09 PM
Thanks for the reply Joey. I just tried what you said and had no luck. The screen still remains blank with the 5V. I am not sure though what the problem is with the sync. I have tried with a couple of sources and the screen still remains black, but everything else appears to be working.

Jomac
8th July 2008, 12:54 AM
Thanks for the reply Joey. I just tried what you said and had no luck. The screen still remains blank with the 5V. I am not sure though what the problem is with the sync. I have tried with a couple of sources and the screen still remains black, but everything else appears to be working.

Do you know if the tube is any good ?? , a quick way to see if the tube is working is to remove one end of any of 3 large resistors on the neck board , this will drive the associated color flat out bypassing any of the blanking circuit on the chassis .

Berty
8th July 2008, 08:21 PM
Okay, just tried what you said Joey and the tube does indeed work.

A couple of things though...

1. I got this chassis and that RGB amplifier had been cut off. The wires are there, but no board... would this be causing the issues?

2. The input pins say R,G,B,E,NC,S... I take it that the E is for the ground? (NC, not connected i.e. a space)

Berty
8th July 2008, 09:10 PM
Follow-up...

Re connected the RGB amp with a spare one I had here and there is no change. I measured the voltage output of the RGB lines and am getting a healthy 6.8Vpp

Berty
8th July 2008, 10:22 PM
Follow-up #2

Used a different harness and still having the same issues, but this time i was turning some of the dials on the remote control board and the anode cap started going ape shit... It was arcing a lot. I believe that the V-Sync adjustment might have set it off