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Power on a cv board


Jinks
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I've repaired two Colecovision systems using some simple guidelines of my own.

 

The common procedure to detect faults in Colecovision is this:

  • Check power supply voltage.
  • Check activity in Z80 MREQ/IORQ pins, CLK input running at 3.579545 mhz.
  • Check decoder 74LS138 for activity in PSG port output (if BIOS is read correctly, it will turn off PSG sound)
  • Check audio output of SN76489 with headphones (if BIOS is read correcly and 74LS138 works, it will be silent at boot-up, otherwise a tone will be heard)
  • Check decoder 74LS138 again for activity in VDP port output (if RAM works correctly, Colecovision will try to init VDP)

If there is activity in VDP port output then you could try a game that starts immediatly with sound (I've used Frogger ;) ) and check with headphones directly in SN76489 audio output. From there you can route and check if VDP chip is damaged or TV output doesn't work.

 

Sometimes can be so simple as the channel switch not in channel 3 ;)

 

Don't forget to download Colecovision schematics from here http://www.atarihq.com/danb/files/colecovision.pdf

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So I think my power supply is right going by what they say online for schematics.

Possibly my RF modulator is no good but you think pressing buttons on the controller would change the picture.

I only have a DK cart so can not do the frogger test.

I will see what else I can do..

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So I think my power supply is right going by what they say online for schematics.

Possibly my RF modulator is no good but you think pressing buttons on the controller would change the picture.

I only have a DK cart so can not do the frogger test.

I will see what else I can do..

 

Hmmm... With the DK cartridge press 1, you should hear the background music in the SN76489 output.

 

I forgot it, you can extract directly the composite video from pin 38 or 36 of the video processor using the RCA cable and two clips (one to ground, other to the signal), this way you can check if the RF module is bad.

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Ok u13 and u14 are corroded and getting hot if i tap them the picture kinda changes so that must be the problem. should change all 8 of them.

Do you know where to get any of these chips??

 

I bought from here http://www.ebay.com/itm/291440640032?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

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  • 2 weeks later...

Ok so I replaced the chips and can hear sound sometimes and the game starts when pressing a button and can move Mario and get killed by a barrel without even seeing anything on the screen.

I found 2 traces bad on my board for the ram chips but now I want to go back and check more as I think I have another trace broken. I also took apart the RF box and checked the circuits there and all looks ok. What channels did these run on 2-3 or 3-4. What pin locations are the ram chips If I am looking at them vertically with them on the bottom right of the board what is pin 1 and 8 and what is 9 and 16. I am looking for schematics and only can find a homemade one which shows many pins all together and does not make much sense. Also my question symbol on my keyboard does not work sorry. Any help is would be great. I am determined after a 12 hour day on it to get it working today.

 

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Hmmm... With the DK cartridge press 1, you should hear the background music in the SN76489 output.

 

I forgot it, you can extract directly the composite video from pin 38 or 36 of the video processor using the RCA cable and two clips (one to ground, other to the signal), this way you can check if the RF module is bad.

To check the video output on the rf xould you give me directions as if your talking to an idiot? I can not seem to see 38 or 36 on the board. I have the top board of the rf circut unsoldered as of now from the 7 pin extension terminals from the main board. I am sure I can tear apart some headphones and a rca cable to make this work. Ia the audio amplified enough to hear it in headphones? and you saying 36 or 38 and to ground on the other wire then to the composite on the tv should see a good picture? I can not find 36 or 38 on the rf board. I am sorry I need further explaination as have spent lots of time on this and need someone to give me some help. If If I figure it out I will buy grips's coleco arcade controller.
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To check the video output on the rf xould you give me directions as if your talking to an idiot? I can not seem to see 38 or 36 on the board. I have the top board of the rf circut unsoldered as of now from the 7 pin extension terminals from the main board. I am sure I can tear apart some headphones and a rca cable to make this work. Ia the audio amplified enough to hear it in headphones? and you saying 36 or 38 and to ground on the other wire then to the composite on the tv should see a good picture? I can not find 36 or 38 on the rf board. I am sorry I need further explaination as have spent lots of time on this and need someone to give me some help. If If I figure it out I will buy grips's coleco arcade controller.

Video processor is the one covered with a heatsink at right of Colecovision motherboard.

 

Pin 1 is at top right and pin 40 is bottom right. Count down to left.

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