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Hey my colecovision , when I first bought it it was having a bad rf problem , so I decide to av mod it , so I followed the ben heck tutorial , and yeah it worked really welll , so time has passed have pased and I decide to use my colecovision again with the expansion module #1 and it worked flawlessly , but when I tested the colecovision without the module (because I dont have games for it ) it showed the colecovision bios screen but all green and with lines , and when the bios disappear the lines still there , however with the expansion module it work flawless , so I thinking my self ok the atari is working because it is it on thing its has it video processor(tia) ,cpu ram etc , buttt it uses the video circuit of the coleco so that tells my that the video circuit is working , so my guess is that the vdp has gone bad or the ram , because I already refurbished the power switch and power supply is working awesome , (btw the picture is way worse with rf but still have the same issues ),(and I already re do the the av mod with new parts and still the same ) anyone that can help me with it ? I am confident with soldering , I replaced the expansion module cpu one time , so im ready for the repair , the only thing is I have to be sure what really is the IC that is making this problem ,thanks in advance for you help

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Some really good advice given to me was use the Coleco frogger game.

 

Your right, the test with exp mod 1 proves RF circuit.

 

Coleco frogger, since it plays music, right from the get go,

will allow you to diagnose either CPU, reset, Sram, controls etc, OR

Vram/VDP. If you get sound but no pic, then its Vram/VDP, no sound, and your

on to CPU clock, etc.

 

​If you Vram is socketed, it might just need to be reseated.

Good luck.

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Test pin 36 to center of RCA jack, ground the side. You should get a crisp B&W picture on your TV, if it isn't then the VDP is bad.

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Test pin 36 to center of RCA jack, ground the side. You should get a crisp B&W picture on your TV, if it isn't then the VDP is bad.

Wheres is pin 36 in the expansion bus orr where ? Thanks very much for you reply

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Wheres is pin 36 in the expansion bus orr where ? Thanks very much for you reply

Pin 36 of VDP chip.

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Pin 36 of VDP chip.

At firts it gave me a garbagr b/w image but I changr to another rca cable , and it gave me a clean b/w picture , so I left it there turn on , and try to replecate de bad b/w image and nop, it was a bad rca cable , so the vdp is not bad :) great , I have the pictures , i will upload them later , but still i haven find whats wrong with my colecovision :(

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Ok, you have a probably good VDP and the colors in expansion module #1 are looking well.

 

So the problem would be in the R-Y and B-Y pins route.

 

Check R40, C62, C66, R41, C63 and C67, probably a capacitor has a broken leg.

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thanks man you really help me out to repair my colecovision , so I desolder de video board from the main boad and looked around and none of the resistor or capacitors where bad but I choose to reflow the solder on them and when I solder back the video board I noticed some broken traces where the two board meet up so I fix them with a wire and yayy it works like it should do , I dont know if it was a bad solder joint on the caps or the broken traces on the board but hey it works now thank you very much man

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