Hi, I just bought a colecovision at a garage sale and I couldnt get it to work with the RF switch so I thought there might be a problem with it. So I figured it wouldn't hurt to try the composite video mod on it, so I have that hooked up properly now and all I get is red or green wavy lines on the screen (which is more than before). If anyone knows of any common fixes it would be great if you could share. Thanks.
-Tim
Colecovision issues
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HomicidalBarber
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phantom92opera
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HomicidalBarber
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GonzoMPM-1
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Get some spray contact cleaner and work the heck out of the power switch.
Also, clean the cartridge contacts.
The red screen issues are something I had come up with a portable I'm working on, and the problem was during testing I was only using the original power supply and switch.
These switches are prone to these problems.
Also, clean the cartridge contacts.
The red screen issues are something I had come up with a portable I'm working on, and the problem was during testing I was only using the original power supply and switch.
These switches are prone to these problems.
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GonzoMPM-1
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Well, I did Coleco stuff all afternoon and have some observations:
1. The Coleco power switch almost certainly is PART of your problem. Best to simply replace it. You'll have to find at least a DPST switch, with a sliding mechanism. Get one rated 1 amp at 5 volts and at least .3 amps at 12 volts. They're easy to find. To replace the switch, you'll want to desolder the "metal bracket" that is around it, then pry the two crimps from the bracket on each side off the switch itself and pull the top of the switch and bracket off. Then replace your switch but hot glue or epoxy the new one to the same metal bracket (you may need to bend the terminals of your new switch or run some wires to get things were they need to be), as the metal bracket is what will let you keep using the original "approach" to the switch in terms of the external lever and casing.
2. Check the "fit" or tension of the pins from the power supply to the power supply "in" connector. In most cases, it will be loose and intermittent. Use needle nose pliers to slightly bend the pins on the machine connector side -- just very slightly -- so they make good connection with your power adapter connector. Also use a properly sized wooden dowel -- a barbQ skewer works well, wrapped with fine sand paper to clean the inside of the holes on the power supply cable.
3. You may consider desoldering the 4 power wires (G, +12, +5, -5) where they reach the mother board. Snip an eighth of an inch off, tin the leads, and resolder. You have to remember that there will be 25 years of corrosion at that area.
4. The video mod most people use involving a 2n4401 transistor is a good one, but does not work with all composite receivers in all televisions, especially more modern ones, and, most especially if they are sensitive to voltage matching and impedance. Do this: Add to the output stage (right before your video output jack, a 16V 47uf electrolytic capacitor ("+" side connected to the signal from your amplifier circuit),, followed by a 75 ohm resistor. So it should go:
You can see the 75 ohm and 50ish uf capacitor in the output stage of the reference circuit on the datasheet for the IC in that Coleco daughter board here (this IC doesn't just create a signal for RF, but combines the signals from the Coleco video chip into real "composite":
http://pdf1.alldatasheet.com/datasheet- ... M1889.html
(click the view link, then the download sheet option, then see page 3-110 figure one, and look at the output stage on the right).
The last bit may not be necessary for your TV once you fix the issues with the switch and power supply, but in my experience this afternoon with 5 different televisions (I actually went around my condo and tried it out on other folks TVs), the additional bits on the output stage are well worth it.
(As an aside, I tried this first with a 100ohm potentiometer. Most of the TV's worked best around 73 to 77 ohms, but there was one --a newer big screen--, that really liked the resistance on this output stage dialed down to 40 ohms, don't ask me why). As to the last, it worked OK with the 75 ohms, but had some signal weakness on parts of the screen during high intensity scenes -- e.g., the all blue game scene selection screen, and similar). This is more of a give away on the limits of the 2n4401 circuit than anything else, but there you go.
One final observation: Don't pull audio right off the audio I.C. if you plan on using an Atari expansion module for the Colecovision. The reason is that there's some switching circuitry that switches to a different audio input (from the Atari module) when its plugged in. Instead, take audio from the daughter board's connector, 2nd from the back of the machine, i.e,. the row of pins on the right side within the daughter board RF box).
1. The Coleco power switch almost certainly is PART of your problem. Best to simply replace it. You'll have to find at least a DPST switch, with a sliding mechanism. Get one rated 1 amp at 5 volts and at least .3 amps at 12 volts. They're easy to find. To replace the switch, you'll want to desolder the "metal bracket" that is around it, then pry the two crimps from the bracket on each side off the switch itself and pull the top of the switch and bracket off. Then replace your switch but hot glue or epoxy the new one to the same metal bracket (you may need to bend the terminals of your new switch or run some wires to get things were they need to be), as the metal bracket is what will let you keep using the original "approach" to the switch in terms of the external lever and casing.
2. Check the "fit" or tension of the pins from the power supply to the power supply "in" connector. In most cases, it will be loose and intermittent. Use needle nose pliers to slightly bend the pins on the machine connector side -- just very slightly -- so they make good connection with your power adapter connector. Also use a properly sized wooden dowel -- a barbQ skewer works well, wrapped with fine sand paper to clean the inside of the holes on the power supply cable.
3. You may consider desoldering the 4 power wires (G, +12, +5, -5) where they reach the mother board. Snip an eighth of an inch off, tin the leads, and resolder. You have to remember that there will be 25 years of corrosion at that area.
4. The video mod most people use involving a 2n4401 transistor is a good one, but does not work with all composite receivers in all televisions, especially more modern ones, and, most especially if they are sensitive to voltage matching and impedance. Do this: Add to the output stage (right before your video output jack, a 16V 47uf electrolytic capacitor ("+" side connected to the signal from your amplifier circuit),, followed by a 75 ohm resistor. So it should go:
Code: Select all
[2n4401 AMPLIFIER OUTPUT ] >> ------- |( ----- /\/\/\ ---- > [output]
47uf 75 ohm (to center connector of composite out jack)http://pdf1.alldatasheet.com/datasheet- ... M1889.html
(click the view link, then the download sheet option, then see page 3-110 figure one, and look at the output stage on the right).
The last bit may not be necessary for your TV once you fix the issues with the switch and power supply, but in my experience this afternoon with 5 different televisions (I actually went around my condo and tried it out on other folks TVs), the additional bits on the output stage are well worth it.
(As an aside, I tried this first with a 100ohm potentiometer. Most of the TV's worked best around 73 to 77 ohms, but there was one --a newer big screen--, that really liked the resistance on this output stage dialed down to 40 ohms, don't ask me why). As to the last, it worked OK with the 75 ohms, but had some signal weakness on parts of the screen during high intensity scenes -- e.g., the all blue game scene selection screen, and similar). This is more of a give away on the limits of the 2n4401 circuit than anything else, but there you go.
One final observation: Don't pull audio right off the audio I.C. if you plan on using an Atari expansion module for the Colecovision. The reason is that there's some switching circuitry that switches to a different audio input (from the Atari module) when its plugged in. Instead, take audio from the daughter board's connector, 2nd from the back of the machine, i.e,. the row of pins on the right side within the daughter board RF box).
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HomicidalBarber
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GonzoMPM-1
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No problem.HomicidalBarber wrote:Wow, thanks for all the help, I will be sure to try all of this.
One more thing: It is my sense that the traces and connection between the RF box and its daughter board and the motherboard proper may be damaged by 25 years of pushing and pulling of an RF cable against the same.
That being the case, if you find other solutions do not help, you may need to resolder (heat to a shine with some new flux and a drop of new solder) each of the connection spots. In the case of lifted traces or pads, you're in luck because those within the RF box itself are only single sided traces, and you can solder shunts as necessary to make sure the signals coming in get to where they are going.
Don't know if that's in any way your problem, and I've not seen it, but there you go.
Good luck.