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orkybork

Colecovision Green screen issue

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Posted (edited)

Hello everyone, back in December I acquired a colecovision from a family member and when i got around to testing it I got this. A big green striped rectangle with a blue border covering the screen. I was able to start games you could hear them play and I could move around and what not but this is what was on screen. I've looked around and i've seen other people who have a green tint on an otherwise working colecovision display. But didn't have the same issue as this. Perhaps one of the chips inside is truly screwed? Any ideas or help? and do let me know if there's any other pictures you'd like to see to further help.

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IMG_4461.JPG

Edited by orkybork

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Hi Orkybork.  That is a rather odd looking screen.  Do you get that same exact screen every time you turn the console on or does it look different each time?  Does it give you the Colecovision screen if you turn it on with no game in it?  If it's the same exact screen image each time with or without a game then that wouldn't be a power issue.  That also doesn't look like a ram issue either.  First thing I would do is change out all the electrolytic capacitors just to rule that out and it's the easiest (and cheap too). Then I would direct my attention to the TMS9928 vdp next.

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Yes it gives this screen every time regardless if there's a game in the console. Here's what the Capacitors look like on my console.

IMG_4465.JPG

IMG_4466.JPG

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That actually looks just like part of the VDP test pattern that comes up when using a diagnostic rom? Only it has a few colored boxes that appear within the green stripes pattern.

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4 hours ago, -^CrossBow^- said:

That actually looks just like part of the VDP test pattern that comes up when using a diagnostic rom? Only it has a few colored boxes that appear within the green stripes pattern.

So does that mean that maybe this thing isn't broken? I'm not sure what else to do at this point. Of course if i don't have to replace anything that would be nice :) but maybe I'll have to.

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On 5/13/2021 at 4:26 PM, orkybork said:

So does that mean that maybe this thing isn't broken? I'm not sure what else to do at this point. Of course if i don't have to replace anything that would be nice :) but maybe I'll have to.

If you can solder and have the means, preferably a desoldering iron, you could try replacing the VDP (it's a TMS 9928 chip, easily found on Ebay). That will at least rule out or solve the issue.

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unknown.png

On 5/21/2021 at 3:06 PM, Ianr757 said:

If you can solder and have the means, preferably a desoldering iron, you could try replacing the VDP (it's a TMS 9928 chip, easily found on Ebay). That will at least rule out or solve the issue.

So this would be the VDP chip I'm guessing based on what I looked into, again this photo is from my CV. Or is it the NEC D780C that needs to be replaced, that's the CPU though If i'm not mistaken. and now suppose I buy this https://www.ebay.ca/itm/222387146999?hash=item33c74e90f7:g:plUAAMXQ97RRHEk9 then I should be on the right path correct?

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7 hours ago, orkybork said:

unknown.png

So this would be the VDP chip I'm guessing based on what I looked into, again this photo is from my CV. Or is it the NEC D780C that needs to be replaced, that's the CPU though If i'm not mistaken. and now suppose I buy this https://www.ebay.ca/itm/222387146999?hash=item33c74e90f7:g:plUAAMXQ97RRHEk9 then I should be on the right path correct?

Yup, that's where I buy mine from. You should buy a heat sink for it too, as it tends to get hot, and some thermal glue to tack it on:

https://console5.com/store/thermally-conductive-heat-sink-adhesive-glue-gd9980-10-grams-10g.html

https://console5.com/store/dip40-super-heat-sink-glue-on-thermal-epoxy-style-dip-40.html

Also, you are correct, that NEC chip is the CPU.

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Ok wow I'm silly, I just realized that this is the chip, not the one I posted right before. I was confused by the amount of pins on the chip. Now then, about this. TMS9928AN vs TMS9928ANL. Is there a difference between the 2,does it matter which one goes in the system? They are the 2 ones that pop up when I search "tms 9928" on ebay.
 

image.png

s-l1600.jpg

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7 hours ago, orkybork said:

Ok wow I'm silly, I just realized that this is the chip, not the one I posted right before. I was confused by the amount of pins on the chip. Now then, about this. TMS9928AN vs TMS9928ANL. Is there a difference between the 2,does it matter which one goes in the system? They are the 2 ones that pop up when I search "tms 9928" on ebay.
 

image.png

s-l1600.jpg

There shouldn't be any problem with using either one. However, I can only vouch for the one you have pictured, sold at the provided Ebay link. I've bought several of these and they work fine. I would be careful buying anything coming from China, though, as I have heard stories of similar ICs (such as the TI99/4a's TMS9918 chip) being purchased from China and not working: 

 

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