A most aggravating ColecoVision experience

[Jess Ragan]

On a whim, I decided to spend the night modifying my old ColecoVision motherboard, using these instructions on Ben Heckendorn's site:

 

http://www.benheck.com/Games/Coleco/Video_Mod.htm

 

After soldering everything into place, I tested it out on my LCD television set. It worked all right at first... the picture was crisper than the 5200 video mod I performed earlier this week, with less of those annoying vertical stripes on the screen. However, after ten minutes, the television started crackling and sound effects would intermittently get all high-pitched and screechy. So I unplugged the system, brought it back to my work table, and moved the sound cables to the underside of the ColecoVision, hoping to get a better connection to the system's sound chip.

 

I brought the system back to the television set, hook it up, and get about fifteen minutes of crisp audio and video. Then I popped in Montezuma's Revenge, and lo and behold, I'm right back to the crackling and distortion. Does anyone know what could be causing this? Could the sound chip be damaged? Should I move the sound cables elsewhere on the motherboard? I don't know what I could have done wrong, because I followed Heck's directions to the letter and I'm still getting lousy sound. Any help would be greatly appreciated!

[+remowilliams]

Does that mod kill the RF out? I'd check there first to see if the sound problem persists.

[Ikrananka]

I can't help, but maybe you could ask someone who is involved in professionally modding these systems, e.g.:

 

Viking Video Games

 

8BitDomain

 

Old School Gamer

[Prodos8]

I've done Ben's CV mod and it seems to work fine for me. You should really pull the sound from a spot inside that RF modulator, that way if you'll get sound when using the 2600 expansion module . The sound source is on the same row of pins that you pull +12 from IIRC it the second pin from the back of the RF modulator. I've done two this way and haven't had any problem yet. BTW I love this mod because its so simple.

 

You could have a bad wire or poor solder joint off of the RCA jack or your cable is bad?

[Jess Ragan]

Oooh... maybe I should give this a shot! I don't like the audio cables on the underside of the motherboard, and would be more comfortable with them resting next to the video cables. Also, it's entirely possible that there's something wrong with the cables I used... I pulled them from an old Famiclone I bought from Goodwill for four dollars. I would have used jacks instead but I didn't have any to spare when I started this mod... it was a spur of the moment thing.

[Bill Brasky]

Sometimes the audio or video signal is too hot for your TV and it'll be fine for a while then start distorting.

[Jess Ragan]

Would resistors help deal with this extra heat?

Edited October 24, 2007 by Jess Ragan

[Bill Brasky]

Would resistors help deal with this extra heat?

 

Have you tried tweaking that mini-potentiometer? When I did the A/V mod, I didn't do it in the RF modulator box. I used different parts and yeah I'm sure you had to put something in between to bring it down to a signal level the TV could handle. I tried simplifying the circuit before by eliminating parts and I ended up with a hot signal that would tear at the top of the screen and there would be color variations where it would be too saturated or washed out. A modern HDTV might be less forgiving than an older analog TV. There are simpler looking A/V mods like the one you're doing. I recall seeing one that used an IC in the circuit, perhaps to get S-video. The one I used was an old one from the 80's, where someone just copied the A/V circuitry from the ADAM and applied that to the CV board.

[joeybastard]

Funny, that it's Montezuma's Revenge causing the problem. MY CV is hooked up using the RF to Coax adapter and when I play Montezuma's Revenge, the sound gets distorted every time I grab something. When this happens the little light on my monitor that registers stereo lights up too but stays dark for all of the other sound effects. I always thought it had something to do with the Montezuma's Revenge cart itself since that's the only one that does it.

Edited October 24, 2007 by joeybastard

[Jess Ragan]

I thought that may have been just a coincidence, but since you're having issues with it too, I have to wonder...

 

I've got the potentiometer cranked up to its maximum resistance level. It's the only way I can get a video signal... anything more than a quarter turn counterclockwise and the picture vanishes completely! I may spend a little more time with this mod, because as it is now I'm not totally satisfied with it. I don't know where I left my Expansion Module but if I ever find it, I'll have to rewire the mod in order to play 2600 games.

[Bill Brasky]

Try a lower value pot. Maybe that's all it needs.