colecovision composite mod question

[bah]

I had a lot of static in the RF signal on my Colecovision so I decided to try a composite video mod. Ben Hecks mod looked easy and it is. The video is clear but considerably washed out as mentioned by others who have tried the mod.

 

Firstly, has anyone ever found a solution to darken the colors. Maybe another video connection point?

 

Secondly, when I turn off the game (turn off main power), the game picture goes off but the game sounds continue indefinitely and you can even play without a picture until you pull the power cord from the wall. When I remove the base connection on the transistor, the console shuts off normally. Can someone verify that this is typical with the mod or have I got something touching that is feeding power back into the console.

 

Thanks

 

BAH

[ApolloBoy]

I also did Ben Heck's mod and I didn't have the sound problem you described. Are you sure everything's soldered to the correct points?

[bah]

Apolloboy,

 

Thanks for the reply. I dug out my Coleco parts system last night. It had no sound and the picture was almost un-viewable because someone had jammed something into the channel select slot and cracked the RF circuit board. I took the same exact components and re-soldered them to the same points on the 2nd Coleco and the video mod worked normally. It shuts off fine. Now my junk console just became my main one. I plan to re-try the mod on my first console again to see what went wrong later today.

 

For what its worth I am getting a slightly darker picture by connecting to pin 6 on the jumper pins between boards instead of using the location shown in Bens mod picture.

 

bah

[GonzoCV-1]

Ben Heck's mod can be improved by adding the proper output stage.

 

You need to take the wire off the transistor that normally goes to the Video signal to your television, and add a 47uf capacitor followed by a 75 ohm resistor. The capacitor removes the DC component of the signal and the 75 ohm resistor provides impedance matching.

 

Once you do this, you'll need to re-trim the circuit to get the signal where you want it. One thing to take care of is to make sure you're not driving it so hard that it clips the signal on saturation screens. (E.g., the Gorf mothership explosion or the white flashes when you use a smart bomb in Defender). On an LCD TV you can tell the signal's clipping because these bright scenes will "blank" the screen as the video circuit in the screen momentarily shuts off to protect itself.

[bah]

GonzoCV-1

 

Thanks for the info. Just to verify, I need to take the line between my transistor and the video jack and install the capacitor and resistor in line for the reasons you listed. I will try it out soon.

 

bah

[GonzoCV-1]

GonzoCV-1

 

Thanks for the info. Just to verify, I need to take the line between my transistor and the video jack and install the capacitor and resistor in line for the reasons you listed. I will try it out soon.

 

bah

 

 

Yup.

 

 

Like this:

 

[transistor output] >> ------- |( ----- /\/\/\ ---- >	  [to signal wire on RCA video jack]
							47uF	   75ohms