Black & White with 7800 cartridges

[MaximRecoil]

I was recently given an Atari 7800 with three 7800 games sixteen 2600 games. I hooked it up and all the 2600 games played perfectly and never any problems with the color. All of the 7800 games that I tried in it had problems with the color. Most of the time on the opening Atari splash screen you would see mostly black & white with brief intermittent color and then, depending on the game, it would be in black & white or very faded color. I cleaned both the cartridges' PCB contacts and the connector on the machine with a pencil eraser and rubbing alcohol and that improved, but did not fix the situation. After the cleaning, the 7800 games would come in full color for both the Atari splash screen and the game a good deal of the time. Other times it would do the same as before I cleaned it.

 

So, the next time that it came in black & white, I pushed the cartridge forward just slightly from the top of the cartridge (toward the TV) and it instantly went into full color. After that I could wiggle the cartridge back and forth all I wanted while the game was running and it stayed in full color. I tried it on all the 7800 games and that worked every time, without fail. Evidently the machine's cartridge connector is worn just enough that it isn't making a great contact with the cartridge's PCB contacts and that slight push forward is enough to fix it. I don't suppose the 7800 connector is easily replaceable like in a front-loading NES is it?

[+Mitch]

You have to unsolder it so I guess it depends on how good your soldering skills are. You might try looking to see if it's just one of the pins that's bent.

 

Mitch

[Bruce Tomlin]

The cartridge connector should have nothing to do with the color. The game would crash before it would lose color.

 

What you are probably doing is flexing the motherboard and causing a bad solder joint to make contact. There are few things more frustrating than a bad solder joint with a ring crack around a pin.

[MaximRecoil]

I am not pushing it hard enough to flex anything. It is only a slight nudge and the color comes right in.

[MaximRecoil]

This shows how hard I am "pushing" the cartridge to make it go from B&W to color:

 

[Bruce Tomlin]

The fact is, the cartridge slot is only a simple 8-bit bus through which both the CPU instructions and data go through. If it's broken for one, it's broken for all. The chroma doesn't exist until after it comes out of the Maria chip. Like I said, if it were affecting data going into the Maria, it would affect data going into the CPU and cause a crash. And the data going from the cartridge to the Maria doesn't contain color information, just palette indexes. I've seen the 7800 schematics many times. There is NO WAY that a flaky connection between the cartridge slot and the Maria can cause color loss and nothing else.

 

You may think you're not flexing anything, but you are. A cold solder joint can take just a little bit of flexing force to make contact. Torsion on the cartridge slot should be enough.

[MaximRecoil]

Well you were right (or maybe not?). I did find a bad solder fillet but it was on the cartridge connector pins:

 

 

I resoldered that bad fillet and it works perfectly now, color every time no matter how I put in the cartridge. The bad fillet on the cartridge connector; wouldn't that have the exact same effect as if one of the cartridge's PCB connectors was not making a good contact with one of the console's external cartridge connector pins?

[CPUWIZ]

The bad fillet on the cartridge connector; wouldn't that have the exact same effect as if one of the cartridge's PCB connectors was not making a good contact with one of the console's external cartridge connector pins?

 

Yes, 100% the same.