New guy needs help. Black screen

[Dreamcastreviver]

So this is my first post so hopefully I'm not doing this wrong.

I have 2 colecovision consoles and 1 doesn't work. I have confirmed the power supply,  channel  and have cleaned out the power switch. when I turn it on it goes to a black screen so I know it's doing something.  I have some knowledge with retro console repair but not with the colecovision.  I took some pics with Power on to hope someone will see a obvious problem.  thanks for any help and apologies if I did or said anything wrong. thank you! 

[+nanochess]

The Frogger cartridge doesn't require video or any action to start playing music, so it could be a good tester.

 

If it doesn't work, I would suspect of the 1Kx4 RAM memory chips, these tend to fail very fast.

 

[Dreamcastreviver]

6 hours ago, nanochess said:

The Frogger cartridge doesn't require video or any action to start playing music, so it could be a good tester.

 

If it doesn't work, I would suspect of the 1Kx4 RAM memory chips, these tend to fail very fast.

 

thanks for the reply. I have a working one and I notice the rf box chip is hotter then the working one

[Ruggers Customs]

First off check the three voltages feeding to the 4116 dram.  If they're all getting the proper voltages then leave them alone for now.  Break out your scope and check the clock signals.  A full set of schematics and a flow chart can be found at Console5's tech wiki.

 

Two other places to check if a black screen is present

 

1.  If the screen is black with a solid audio tone then it's likely a fault with the Z80.

2.  If the screen is black with no tone or any noise at all then one of your Sram (2114 sram at U3 & U4) chips is likely at fault.

 

This should get you started and good luck!

[Dreamcastreviver]

10 hours ago, Ruggers Customs said:

First off check the three voltages feeding to the 4116 dram.  If they're all getting the proper voltages then leave them alone for now.  Break out your scope and check the clock signals.  A full set of schematics and a flow chart can be found at Console5's tech wiki.

 

Two other places to check if a black screen is present

 

1.  If the screen is black with a solid audio tone then it's likely a fault with the Z80.

2.  If the screen is black with no tone or any noise at all then one of your Sram (2114 sram at U3 & U4) chips is likely at fault.

 

This should get you started and good luck!

so it has one long tone. sometimes it cuts off and sometimes it stays on bit it has some weird mess on the screen with the sound. when the sound stops it goes to a solid black screen.

[Dreamcastreviver]

On 3/2/2024 at 5:34 AM, Ruggers Customs said:

First off check the three voltages feeding to the 4116 dram.  If they're all getting the proper voltages then leave them alone for now.  Break out your scope and check the clock signals.  A full set of schematics and a flow chart can be found at Console5's tech wiki.

 

Two other places to check if a black screen is present

 

1.  If the screen is black with a solid audio tone then it's likely a fault with the Z80.

2.  If the screen is black with no tone or any noise at all then one of your Sram (2114 sram at U3 & U4) chips is likely at fault.

 

This should get you started and good luck!

so also what is the Z80?

[allansim]

Z80 is the CPU of the system.  It's the long chip on the board between the cartridge connector and the expansion slot.  Since you have 1 working colecovision you could swap that chip onto the board that doesn't work to test if that fixes it.  If it works, then the Z80 is bad, but you're in luck because its a very very common easily-found chip that's been used in a slew of different electronics for decades.  Conversely if the Texas Instruments graphics chip was no good though, that'd be harder to source a replacement.

 

I assume you don't get the 'Turn Your Coleco Off' message when you turn it on without a cartridge in it?  If you see that message, the Z80 is probably good and i'd look elsewhere, like cleaning/replacing the cartridge slot.

Edited March 4 by allansim

[+nanochess]

Because of the tone stuck, I would suspect first of the 2114 RAM (there are two of these). Besides I see in your picture one of these gets very hot.

[Dreamcastreviver]

On 3/3/2024 at 8:57 PM, allansim said:

Z80 is the CPU of the system.  It's the long chip on the board between the cartridge connector and the expansion slot.  Since you have 1 working colecovision you could swap that chip onto the board that doesn't work to test if that fixes it.  If it works, then the Z80 is bad, but you're in luck because its a very very common easily-found chip that's been used in a slew of different electronics for decades.  Conversely if the Texas Instruments graphics chip was no good though, that'd be harder to source a replacement.

 

I assume you don't get the 'Turn Your Coleco Off' message when you turn it on without a cartridge in it?  If you see that message, the Z80 is probably good and i'd look elsewhere, like cleaning/replacing the cartridge slot.

it just makes a buzz like sound with fine scrambling screen. I hate to remove anything from my working one but that is a good idea. thank you!

[Dreamcastreviver]

On 3/4/2024 at 5:53 PM, nanochess said:

Because of the tone stuck, I would suspect first of the 2114 RAM (there are two of these). Besides I see in your picture one of these gets very hot.

thank you im not sure what one that is I will have to go look again