CV garbled start screen a couple of questions

[omgaz]

I have a CV that I have been meaning to fix for a long time -- and its finally time. It has always had the garbled screen on boot. If I put a cart in, it does appear to play the game(audio and movement on screen), however I cannot make anything out. The power supply has the correct voltages. I disassembled the power switch, cleaned and greased it and no change. I suspect the video ram is on its way out. I was probing around with a multimeter and when I check for resistance on pin 11 of the bottom right memory chip, the missing letters in colecovision appear and almost everything else goes out on the screen. Because of this I think I am going to replace them all with the 4161 chips and sockets.

 

Are these the correct chips?

eBay Auction -- Item Number: 180613081623

 

Does it sound like i'm on the right path to getting this fixed?

 

pic of boot screen

[Inky]

I have a similar problem with my ADAM

[Yurkie]

I have a CV that I have been meaning to fix for a long time -- and its finally time. It has always had the garbled screen on boot. If I put a cart in, it does appear to play the game(audio and movement on screen), however I cannot make anything out. The power supply has the correct voltages. I disassembled the power switch, cleaned and greased it and no change. I suspect the video ram is on its way out. I was probing around with a multimeter and when I check for resistance on pin 11 of the bottom right memory chip, the missing letters in colecovision appear and almost everything else goes out on the screen. Because of this I think I am going to replace them all with the 4161 chips and sockets.

 

Are these the correct chips?

eBay Auction -- Item Number: 180613081623

 

Does it sound like i'm on the right path to getting this fixed?

 

pic of boot screen

 

You said 4161, it's 4164...however your link is right and I have purchased from that Ebay seller and she is top notch. Now the bad news. I doubt you have bad DRAM(S), so replacing them will likely not solve your problem. Also you can't check a resistor "in circuit" accurately with a multimeter, you need to desolder one side to check it. I also highly doubt that you have a bad resistor. If I where going to blindly guess on an IC swap, I would say the VDP. Unless you are extremely skilled in soldering, attempting to replace a VDP without damaging the PCB is highly unlikely. There are however other things that can cause video problems and diagnosing via a forum is pretty much an act in futility. Aside from refurbishing the power switch, repairing a ColecoVision is a lot more involved than a Google search and a soldering iron.

[omgaz]

Hmmm well thats not what i was hoping to hear. Is there any way to narrow it down further as to what the problem is? I am not that skilled at soldering, however I have replaced 40 pin ICs before with success and this one looks no different. Is there a way to test the VDP?

[omgaz]

 

You said 4161, it's 4164...however your link is right and I have purchased from that Ebay seller and she is top notch. Now the bad news. I doubt you have bad DRAM(S), so replacing them will likely not solve your problem. Also you can't check a resistor "in circuit" accurately with a multimeter, you need to desolder one side to check it. I also highly doubt that you have a bad resistor. If I where going to blindly guess on an IC swap, I would say the VDP. Unless you are extremely skilled in soldering, attempting to replace a VDP without damaging the PCB is highly unlikely. There are however other things that can cause video problems and diagnosing via a forum is pretty much an act in futility. Aside from refurbishing the power switch, repairing a ColecoVision is a lot more involved than a Google search and a soldering iron.

 

 

I bought a logic probe and it appears the memory is OK. Is there a way to test the 9928 chip with a logic probe? Because I a can't seem to find any help/documentation on the internets i am going to replace the 9928 chip. If that doesnt work i guess it'll go in the closet for another 10 years.