ColecoVision RF Unit & Video Circuit Photos

[Ikrananka]

While recapping one of my ColecoVision's I removed the RF unit to get access to the two electrolytic caps located on the motherboard beneath it and also the one on the RF daughterboard.  I don't recall having ever seen photos of the RF unit's component side or the associated video switching circuit that is beneath the RF unit on the motherboard.  So, before I reassembled everything I took a load of photos in case they were a useful reference to anyone else.

 

I took photos from lots of angles as well as close ups of component labels.

 

CV Motherboard Rev.J

RF Unit Daughterboard Rev F

 

Note that I took the photos after I installed the new capacitors, hence the electrolytic caps in the photos are the new ones and not the originals.  They are all 10uF.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited June 19, 2019 by Ikrananka

[Pixelboy]

I didn't think the insides of an RF unit were so... colorful. 

[Ikrananka]

Just now, Pixelboy said:

I didn't think the insides of an RF unit were so... colorful. 

I particularly like the luminous green 8 pin riser ?

[Pixelboy]

2 hours ago, Ikrananka said:

I particularly like the luminous green 8 pin riser ?

 

I'll bet you a dime it glows in the dark when it heats up. 

 

[ChildOfCv]

I'm amazed at how clean it is.  Or did you put it through an ultrasonic while it was apart?

[Ikrananka]

7 hours ago, ChildOfCv said:

I'm amazed at how clean it is.  Or did you put it through an ultrasonic while it was apart?

The motherboard was a little dusty but I gave it a good clean with alcohol and it came up a treat.  The RF board was lovely and clean as it was.

[MMarcoux66]

Are the RF boxes interchangeable between versions? I have 2 CVs each showing different issues. One is a Rev A motherboard with a rev B RF box and the other is a Rev H2 with a Rev E rf box. The rev A CV that is only showing black and white but otherwise works fine and the H2 is showing a clear picture but characters are scrambled on the screen. H2 prob has bad RAM.

 

So, was thinking of flipping the RF boxes to get one working CV.

 

 

[+-^CrossBow^-]

I literally ran into this black and white only issue on a CV sent to me yesterday to take a look at. What I noticed was that when I removed the cover off the RF box, color suddenly came back?! I looked and looked and could NOT find a reason for this. But I did noticed that if I pressed on parts of the RF board near the riser section, that the color would come and go. None of the solder joints appeared to be cracked but I went ahead and 'fixed' it by applying some heat a tiny bit of new solder to each of the pins along the row and a few others that looked suss just in case. Seems to have corrected it for now so that is something to look for. Especially as that top RF board is single layer so the only solder used is what you can see. So you might see if you can get the color to come back by simply touching up all the solder points.

 

 

[MMarcoux66]

I'll give it a try! Thanks for the suggestion. The crazy thing is that it looks like someone did a lot of work on that box. 

 

[+-^CrossBow^-]

The one I'm working on now was sent to me because the RF wasn't really working at all. I found the entire upper PCB separate from all 6 ground points around the RF box. Likewise there were quite a few cracked solder joints due to the movement of the board essentially floating at that point. Some corrosion on the bottom side of the board as well that I had to scrape away and apply some new solder to. But after all that I had working RF but it was doing two things I hadn't seen before. It would work fine until I put the top back on the RF box. Then the color would immediately drain from the picture and I would usually lose sound? That was when I found that pressing down on the board was still causing some oddness and touched up all the solder joints at that point.

 

The one I'm working on, I can tell I'm not the first person inside it because the center screw near the cartridge port and the one the upper right that hold the actual PCB down to the bottom shield section, weren't even tightened all the way down to begin with. There was good 2mm gap in fact on the center screw in the center. Don't think it left the factory that way.

 

[+-^CrossBow^-]

On 6/19/2019 at 3:32 PM, Ikrananka said:

While recapping one of my ColecoVision's I removed the RF unit to get access to the two electrolytic caps located on the motherboard beneath it and also the one on the RF daughterboard.  I don't recall having ever seen photos of the RF unit's component side or the associated video switching circuit that is beneath the RF unit on the motherboard.  So, before I reassembled everything I took a load of photos in case they were a useful reference to anyone else.

I usually install the replacement caps on the bottom of the PCB and on the top of the upper daughter board so they can be replaced in the future without having to remove the RF modulator to get to them. I also find it MUCH easier to just de-solder and remove the entire assembly from the bottom of the PCB vs trying to crack loose all the ground tabs at the top and remove just the upper board. That is what you did as could be seen in your pics.

 

[Ikrananka]

4 minutes ago, -^CrossBow^- said:

I usually install the replacement caps on the bottom of the PCV and on the top of the upper daughter board so they can be replaced in the future without having to remove the RF modulator to get to them. I also find it MUCH easier to just de-solder and remove the entire assembly from the bottom of the PCV vs trying to crack loose all the ground tabs at the top and remove just the upper board. That is what you did as could be seen in your pics.

 

I went the whole hog with removing the RF unit because I really wanted to see the components underneath to photograph them.  More a curiosity thing on my part.  Not sure what you mean though by "crack loose" all the ground tabs.  I used a desoldering station that made short work of removing the solder from the ground tabs under the motherboard, and then just a slight bend of the tabs with pliers.  No cracking involved ?  I also left the daughterboard in the RF shield so am confused what you mean about me removing just the "upper"(?) board???  The most difficult part I found was desoldering the 8 pin header.

[+-^CrossBow^-]

I meant trying to remove the daughter board from above instead of removing the entire RF modulator. Before I got wise, that is basically what I was doing until I got my de-soldering iron to help with removing the RF box completely.

 

By cracking I meant removing and de-soldering the top board from the ground anchors along the top of the RF box.

 

 

[Ikrananka]

I'm still confused.  I didn't remove the daughterboard from the top and didn't even attempt to do that.  I desoldered the entire RF box, including desoldering the header, from the bottom of the motherboard and removed the RF box complete with daughterboard still inside.

[+-^CrossBow^-]

30 minutes ago, Ikrananka said:

I'm still confused.  I didn't remove the daughterboard from the top and didn't even attempt to do that.  I desoldered the entire RF box, including desoldering the header, from the bottom of the motherboard and removed the RF box complete with daughterboard still inside.

Nothing to be confused about. But I've done this in the past before I got my de-soldering iron making this much easier now. Guess I was the only one attempting that LOL!

 

[Ikrananka]

My confusion stems from the fact that I believe I did the same as what you say you're doing and yet you seem to be saying that I did something different to what you did.  Hence my confusion.

[+-^CrossBow^-]

Oh! Gotcha. No I meant at least you weren't trying to do it that way. I misunderstood. I was stating what I did in agreement with you. Other than my installing the caps outside the RF modulator.

 

 

[ChildOfCv]

The first time I removed my RF box, the 8 pin link between the boards just stubbornly refused to let go.  I did get it loose eventually, without tearing traces.

 

I remember removing the box again later, and that time I unsoldered the whole thing, top and bottom, so that the surround metal could be removed and the pins were easier to work with.

 

2 hours ago, -^CrossBow^- said:

The one I'm working on now was sent to me because the RF wasn't really working at all. I found the entire upper PCB separate from all 6 ground points around the RF box. Likewise there were quite a few cracked solder joints due to the movement of the board essentially floating at that point. Some corrosion on the bottom side of the board as well that I had to scrape away and apply some new solder to.

Yikes.  Makes you wonder what kind of abuse it suffered.

[ChildOfCv]

7 hours ago, MMarcoux66 said:

I'll give it a try! Thanks for the suggestion. The crazy thing is that it looks like someone did a lot of work on that box. 

 

 

Well, now looking at the 1K resistor, it is in parallel with another 1K resistor to ground.  Or... is it replacing that resistor?  The existing 1K is south of the LM1889 chip.  I wonder if the PCB suffered some physical abuse and some parts got disconnected by broken traces?

 

The 33K resistors seem to be replacements for the 39K resistors that should be making those same connections.

 

The diode replaces the zener regulator that sets the sound mix bias voltage.  Well, this voltage also biases the component video inputs too.

 

Interesting that all components involved have something to do with audio.

 

Edited August 4, 2021 by ChildOfCv

[MMarcoux66]

2 minutes ago, ChildOfCv said:

 

Well, now looking at the 1K resistor, it is in parallel with another 1K resistor to ground.  Or... is it replacing that resistor?  The existing 1K is south of the LM1889 chip.  I wonder if the PCB suffered some physical abuse and some parts got disconnected by broken traces?

 

The 33K resistors seem to be replacements for the 39K resistors that should be making those same connections.

 

The diode replaces the zener regulator that sets the sound mix bias voltage.

 

Interesting that all components involved have something to do with audio.

 

Yeah, I have no clue what happened to this in the past. When I opened it, it looked like it was wired up like a Christmas tree...  lol. That is why I was thinking about moving the RF box from the other non-functioning CV and simply replacing this one. The other one has no hotwiring to it.

 

Interestingly enough, there are no sound issues...  just b&w picture. I even went as far as putting a composite mod on it and even that was in b&w.

[ChildOfCv]

9 minutes ago, MMarcoux66 said:

Interestingly enough, there are no sound issues...  just b&w picture. I even went as far as putting a composite mod on it and even that was in b&w.

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.

Edited August 4, 2021 by ChildOfCv
Oopsie

[ChildOfCv]

3 minutes ago, ChildOfCv said:

Well, one quick check would be to measure the voltage on the 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.

And for that matter, I just noticed two capacitors camouflaged near the tape.

[MMarcoux66]

1 minute ago, ChildOfCv said:

And for that matter, I just noticed two capacitors camouflaged near the tape.

Yeah, noticed that as well. There are 2 there. I wonder what fun there is under the RF board :).  

[Ikrananka]

1 hour ago, -^CrossBow^- said:

Oh! Gotcha. No I meant at least you weren't trying to do it that way. I misunderstood. I was stating what I did in agreement with you. Other than my installing the caps outside the RF modulator.

Great - I'm glad we're on the same page - my head was hurting.  So, y ou're right and I'm right ?  I do like your idea of replacements being outside - good call.

 

1 hour ago, ChildOfCv said:

The first time I removed my RF box, the 8 pin link between the boards just stubbornly refused to let go.  I did get it loose eventually, without tearing traces.

That's what I had the most difficulty with as well.  I guess it's the long risers wicking away heat and the holes not being plated through.

[MMarcoux66]

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.