ColecoVision RF Unit & Video Circuit Photos

[+-^CrossBow^-]

27 minutes ago, MMarcoux66 said:

So reflowing the solder around the connector didn't help. Think next step is to remove the box completely. I ordered a desolder iron which will be here Friday. Also, it looks like another resistor is on the back of the board near this same area. I hadn't noticed that before. Another view of the box with the tape removed. Looks like it was there to prevent the 2 caps from shorting out stuff around it. 

 

As you have pics of all of this, What about simply removing all of these extra components to see what you get? They aren't normally present on a standard RF box as I've never seen added components like this before other than when I've recapped them to make them easier to get to in the future.

 

[MMarcoux66]

5 minutes ago, -^CrossBow^- said:

As you have pics of all of this, What about simply removing all of these extra components to see what you get? They aren't normally present on a standard RF box as I've never seen added components like this before other than when I've recapped them to make them easier to get to in the future.

 

I did try disconnecting a few of them and the CV would not display a picture. They are definitely being used. That is why I am thinking of taking the rf box from the other CV I have. It has garbled graphics but a clear picture...  

[+-^CrossBow^-]

4 minutes ago, MMarcoux66 said:

I did try disconnecting a few of them and the CV would not display a picture. They are definitely being used. That is why I am thinking of taking the rf box from the other CV I have. It has garbled graphics but a clear picture...  

That would likely be easiest then. I know you can do that as I actually did that with the one I'm working on now. At first it wasn't giving me any picture through RF. I swapped it out with another RF box I had on hand and it worked and that was when I noticed the additional cracked solder joints and the like on the one I removed and was able to get the original working again. And yes, I swapped it back into the CV even though I already installed a working RF modulator as I was trying to keep it as original as I could for the client that owns it.

 

Could try just removing that resistor that is across the IC chip from the bottom of the PCB to see if that changes anything but leaving the rest in place.

 

 

[MMarcoux66]

On 8/4/2021 at 6:38 PM, ChildOfCv said:

Well, one quick check would be to measure the voltage on the NON-banded side of the diode.  From memory, I think it's supposed to be somewhere near 5V.

 

You could also remove the tape to see if there are more hidden surprises.

So, I checked the voltage on both sides of the diode. On the top I am getting 12.4v and on the bottom I am getting 6.56v.

[ChildOfCv]

9 hours ago, MMarcoux66 said:

So, I checked the voltage on both sides of the diode. On the top I am getting 12.4v and on the bottom I am getting 6.56v.

Okay that's good voltage.  It means you likely have good bias for the color components.  Pins 2, 4, and 13 on the IC should be close to that voltage.  Just remember that you're looking at the bottom side, so the pin order is mirrored.

 

And if you have a scope (or can borrow one), look at pins 1 and 18 of the chip.  That's where the 3.58MHz clock is supposed to come in.

Edited August 10, 2021 by ChildOfCv

[MMarcoux66]

So, I haven't gotten time to change out the RF box. My desoldering tool did not work all that well in what time I did have. However, I did try an Atari expansion in both of my broken systems. It came up also as B/W on this unit which tells me that this is an RF box issue.

 

On my other unit which has garbled graphics that I was going to grab the RF box from, the Atari module came up perfect...  So, that one appears to be RAM or the video chip as I suspected. Since I don't feel that I can do the RAM with my skillset ...  my plan is still to take the RF box from this one and try it in the first one.

[MMarcoux66]

Finally got around to flipping the RF boxes and no change. Still black and white. I think that I am going to give up on this one and work on the other. I might try the RAM upgrade as that one only has scrambled graphics. I've seen some have simply cut the legs off the memory chips and soldered the sockets to those. I might be able to handle that :).

 

Thanks again for the pictures and the help with trying to fix the CV.

[ChildOfCv]

On 8/17/2021 at 1:18 PM, MMarcoux66 said:

So, I haven't gotten time to change out the RF box. My desoldering tool did not work all that well in what time I did have. However, I did try an Atari expansion in both of my broken systems. It came up also as B/W on this unit which tells me that this is an RF box issue.

EM1 encodes its own color, and the RF section only has to modulate it to the channel frequency.  If you still get B/W out of it, but otherwise get a clear picture, the fault almost has to lie in the TV (wrong standard?).  The only other thing that could cause an issue is if the clock is running at the wrong frequency.  But that should be apparent from speed of play, and sync/width problems.

[MMarcoux66]

16 hours ago, ChildOfCv said:

EM1 encodes its own color, and the RF section only has to modulate it to the channel frequency.  If you still get B/W out of it, but otherwise get a clear picture, the fault almost has to lie in the TV (wrong standard?).  The only other thing that could cause an issue is if the clock is running at the wrong frequency.  But that should be apparent from speed of play, and sync/width problems.

3 different TVs, same result. So it is definitely not the TVs as other CVs work fine. Definitely puzzling...