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Airshack

Two Mario’s in Donkey Kong?

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While finishing the composite AV mod on my ColecoVision, I noticed something strange. I observed a single Mario character staying at the bottom left corner of the screen while my playable character moved about? A power cycle removed the issue sometimes. I was thinking maybe the typical Coleco bad power switch so I carefully replaced it. Made sure not to cross the 12v and 5v columns. Now I get black screen only when I turn it on? All connections checked and rechecked...black screen on RF out too! No sound! Power tests good from transformer.

 

Any ideas on where to go from here? I ordered a logic probe yet havent used on for 30+ years.

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Is your switch the problem? Can you bypass the switch and wire the thing so it is always powered? Then you'd know if something blew in the Coleco or if it was just the switch not er . . . switching.

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Is your switch the problem? Can you bypass the switch and wire the thing so it is always powered? Then you'd know if something blew in the Coleco or if it was just the switch not er . . . switching.

I replaced the switch and then removed the new switch and wired it always ON. Still, black no sound.

 

 

Sent from my iPhone using Tapatalk Pro

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Did you check the voltages after the switch?

Yes. With the new switch and finally with the switch removed and wired always on.

 

The memory appears the be getting 5v. The CPU around three volts. I’m not really sure what I’m looking for otherwise. Logic probe ordered and hoping to learn some basic diagnostics.

 

Any hints where to start?

 

 

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I’ll need to check everything out in a few days. I’m not sure which pins to check actually. I have research to do...as well as learn how to use my new logic probe.

 

 

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Well, the voltage at the CPU ought to be the same as what comes from the switch. The actual pins to measure are in the middle of the chip, not on the corners like you might be used to.

 

You can measure them directly at the larger coils of wire right next to the switch though. Keep the black probe on the ground strip. With the red probe, one will measure 5V, the other 12V.

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I would say you have a bad RAM chip(s), something wasn't clearing / when you started it and now it just happens to be a dead RAM chip(s). For example the VDP had a standing Mario sprite setup and when the program went to make it not visible by moving it off the screen the RAM did not update, leaving it on the screen.

 

Also did you leave the RF modulator hooked up so you can verify that it is not the composite mod?

 

Milli

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I would say you have a bad RAM chip(s), something wasn't clearing / when you started it and now it just happens to be a dead RAM chip(s). For example the VDP had a standing Mario sprite setup and when the program went to make it not visible by moving it off the screen the RAM did not update, leaving it on the screen.

 

Also did you leave the RF modulator hooked up so you can verify that it is not the composite mod?

 

Milli

 

I did test the still connected RF out. It gives the same display w/ no sound. BTW...the Composite mod worked after a careful install as did th RF out. Only AFTER I modded the power switch did the black screen w/no sound deal happen.

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If you want to replace the RAM chips, console5 sells a kit that uses newer style memory which only needs +5V. Just make sure to follow the instructions to the letter or you'll fry them with +12V instead.

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I am interested yet I’d be more enthusiastic about the RAM mod if I knew it was most likely a RAM problem.

 

 

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Edited by Airshack

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If you want to replace the RAM chips, console5 sells a kit that uses newer style memory which only needs +5V. Just make sure to follow the instructions to the letter or you'll fry them with +12V instead.

I feel I need to discover the problem with an acceptable level of certainty before I try this.

 

 

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Yeah, besides that only replaces the video RAM. There's also two general RAM chips elsewhere.

 

Did you measure the voltage at the coils next to the switch with it turned on yet?

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Sorry about your hardware trouble but right now I can't stop thinking about a two player Donkey Kong with an extra wide, mirrored platform where DK will alternatively throw barrels in each direction and the two players (supposedly Mario and Luigi?) will compete to get to the top first and save Pauline. It makes me wonder if big N* ever made a such game or even considered it.

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