This Arari 2600 Jnr works fine but for some reason the image is only in black and white. I Initially thought that the the switch to change between colour / black and white TV on the console may be faulty.
However switching that switch when on definitely changes the image, indicating the problem is elsewhere.
Looking from the outside there seems to be rust and corrosion on the inside which could be part of the problem.
To open the Atari you need to remove the five screws from the bottom. Then the top of the case will lift away.
You need to be careful to gently remove the ribbon from the connector that attaches the top to the bottom of the case.
Once the top is off you see the RF shield over most of the main board. To take this off unclip the whole of the board from the back of the case.
Once removed turn in over and then bend up each of the little metal clips holding the two halves of the shield together.
Once all of those are open the shield can be taken off the board.
Interestingly the corrosion does not seem to have reached the inside from the shield.
One thing that was very corroded and a very likely cause of the colour problem is the potentiometer that is used to adjust the colour levels.
This is a 500k ohm potentiometer. So I replaced that before doing anything else.
When I took it out it fells to pieces and was full of sticky gunk.
Underneath needed cleaning up with some IP Alcohol.
Then the replacement part was soldered in to place.
Time to test . . .
Reassembling the case was just a case of reversing the steps I took to take it apart.