Help Wanted: Fix My colecovision

[loottool]

Was wondering if anyone could walk my through fixing my Colecovision? I have checked the power supply and I get the correct voltages at the board, the plug, and after the switch.

 

I originally thought the problem was the cartridge slot so I replaced that only to find out that the console should show insert cart screen with nothing in the deck. I guess that was a wasted effort.

 

It was working about 2 months ago and I have had it for about 5 years.

 

The screen shows as a perfectly black screen turning it on and off sometimes creates a screwed up screen (not related to colecovision start screen) and a humming sound. I have checked the reset switch. It makes and breaks as a switch should.

 

I hooked up the expansion mod 1 and plug pac-man in and it works perfectly. so I would guess that the rf modual is working as it should.

 

My best guess is the video chip is bad but I am only guessing from the repair manual I have says check chip u9 video circuit. Anyone know how??

 

and old link with a similar problem but never solved link

 

can anyone help me??

 

thanks

 

I am new here

 

Daniel

Edited November 26, 2010 by loottool

[+5-11under]

Power switch? Give it a blast of contact cleaner, to see if it gets any better... then clean it properly if it does.

VDP chip (with the heat sink)? Replace... easier said than done.

Video RAM? I've got my doubts in this case, but you never know.

Circuitry past the VDP? Try a simple video mod, to see if that works... I've had some successes with this. I've also had it where a component mod fixes it, too.

Edited November 26, 2010 by 5-11under

[loottool]

I feel confident that it is not the switch as I get 12 and 5 volts to and from the switch.

 

Is there a way to check the video chip?

 

if it was the rf then exp mod 1 shouldn't work. right?

 

I am wanting to do the video mod but I am not certain that its going to fix my problem.

 

Thanks for the suggestions.

 

Anyone out there that can help trouble shoot the video chip???

 

Daniel

Edited November 27, 2010 by loottool

[ColecoDan]

I am by far not good at this stuff that is why I send my colecovisions out to get modded or referbed. However I believe the exp mod works totally independent of the colecovision and everything it needs to function is inside the expansion module. I believe it bypasses everything in the colecovision when it is plugged in so I don't think that working tells you anything other than your expansion module is functional.

 

If you were getting messed up graphics then I would say it was the on off switch that needed to be lubbed. Since you are getting nothing I assume it must be what the other guy thought with the video chip. I think yurkie knows how to fix them if you send it to him but not sure if there are directions out there anywhere.

 

Hope that helps a little.

 

Dan

[loottool]

thanks for the response.

 

I thought that the expansion mod was still using the rf of the colecovision to output the signal but I could be wrong.

 

anyone know for sure?

 

Daniel

[NIAD]

thanks for the response.

 

I thought that the expansion mod was still using the rf of the colecovision to output the signal but I could be wrong.

 

anyone know for sure?

 

Daniel

The Exp. Mod. #1 Atari Adapter does use the RF Output of the ColecoVision as well as, of course, power. That is all, the rest is self-contained in the Exp. Mod.

 

Sorry I can't help you with anything else.

[OldAtarian]

Honestly, if it's not something simple it might be better just to get another Colecovision and keep the old one for parts or sell it for whatever you can get for it. I broke one of the controller ports off mine and it had been sitting unused for around 15 years until I found someone selling a motherboard for $20. It wasn't worth the labor charge to fix the old one. Even if you have to buy a complete system with games, you can always sell anything you don't need to get some of the money back. You might even be able to get one with games you don't already have and fill some holes in your collection at the same time.

[loottool]

well I borrowed a logic probe and I also have a diode tester / multi-meter that I am going to try and trouble shoot my system with. If anyone has some pointers or words of wisdom please share them.

 

Thanks

[+5-11under]

What have you tested so far?

[loottool]

To be honest I have only tested the memory with the probe. A friend at work let me borrow it.

 

I really don't know what I am doing when it comes to the circuit board level of electronics.

 

I am trying to learn.

 

I found a post on digital press about the memory posted below. Everything is the same but number 3 I get low/pulse on all the chips at point 3.

 

I really don't think that is the problem. The trouble shooting guide from coleco posted on coleco vision zone leads me to start with chip U9:36

 

to see if that point is good but I don't know what to look for.

 

I believe this is the video chip.

 

I am testing it using the probe connected to negative and +5 off the power supply.

 

I have also checked the voltage all the way to the switch. The voltage it right. past the switch.

 

anything you can do to help is appreciated

 

Daniel

 

From Digital press

 

"Bad memory/RAM chips can result in problems like distorted graphics or text.

Figuring out which chip(s) needs to be replaced can be done easily with a logic probe.

Set the probe to pulse and TTL/LS. Looking at the motherboard (with the cart port towards you),

the memory chips are in the upper-right area and are labeled U10-U17.

With the system on, probe the pins on each chip. Here's what you should be seeing:

 

1) LOW

2) PULSE

3) HIGH

4) PULSE

5) PULSE

6) PULSE

7) PULSE

HIGH

9) HIGH

10) PULSE

11) PULSE

12) PULSE

13) PULSE

14) PULSE

15) PULSE

16) LOW

 

If a pin gives you a different reading than what's listed, the chip is bad and needs to be replaced."