Atari 7800. Fire button stuck on and 2600 games not working

[mamejay]

Hi Guys,

 

Got myself a PAL 7800 and decided to do a basic AV mod on it.

Got the video working fine so I decided to do the audio. I disconnected the the 2 x resisters for the audio and was going to grab the audio from there.

When i fired the system up the built in Asteroids games automatically went into a game. The fire button does not work but everything else does. Seems like the fire button is stuck on.

 

If I try a 2600 cart now I get a flickering bar on screen.

 

It was working for a short while before it died.

 

I reverse the mod but I get the same symptoms now.

 

Any idea of what could be the problem?

[A.J. Franzman]

You broke it.

[mamejay]

Very clever of you. I didn't realise.

 

Now if someone could tell me what chip on the board that could be the problem that would be great.

I suspect the TIA may have a problem as I believe it controls the controllers and the 2600 video.

 

I have some spare 2600Jnr's here that I can steal chips from. Will the TIA from a JNR work on the 7800? From what I can tell they are the same chip.

[DanBoris]

Hi Guys,

 

Got myself a PAL 7800 and decided to do a basic AV mod on it.

Got the video working fine so I decided to do the audio. I disconnected the the 2 x resisters for the audio and was going to grab the audio from there.

When i fired the system up the built in Asteroids games automatically went into a game. The fire button does not work but everything else does. Seems like the fire button is stuck on.

 

If I try a 2600 cart now I get a flickering bar on screen.

 

It was working for a short while before it died.

 

I reverse the mod but I get the same symptoms now.

 

Any idea of what could be the problem?

 

Do 7800 cartridges work?

[mamejay]

I have a PAL 7800 and have only tried the built in Asteroids game. I have a few PAL 7800 games but they are all sealed and I didn't want to open them.

I will try one out and see if that works.

 

The problem happened when I tried to grab the audio signals from R33 and R32. I checked on the schematics for R33 and saw that it it feeds back to the TIA chip. That is why I am suspecting that its that chip.

[Video]

It's possible one of the chips for 2600 gaming is damaged (or unplugged, are those socketed on the 7800) Taht would let the 7800 still run for the most part, at least for stuff that doesn't use the faulty 2600 parts, but not work with the 2600.

 

I doubt your controller broke it though, the systems don't really care how the buttons are held or anything, it just means the stick wouldn't work for it's purposes.

[mamejay]

Thanks for that. From what I have read the TIA controls the Atari 2600 side of things and just the buttons for the controllers. This would make sense that the fire button is stuck on and that the 2600 won't run games if I killed the TIA.

Everything on this board is soldered to the MB but I have a desoldering gun coming and will add sockets to the MB. I have some spare TIA chips that i got to repair some 2600 JNR's.

From what i can tell these are the same for the 2600 and 7800.

[mamejay]

Thanks for that. From what I have read the TIA controls the Atari 2600 side of things and just the buttons for the controllers. This would make sense that the fire button is stuck on and that the 2600 won't run games if I killed the TIA.

Everything on this board is soldered to the MB but I have a desoldering gun coming and will add sockets to the MB. I have some spare TIA chips that i got to repair some 2600 JNR's.

From what i can tell these are the same for the 2600 and 7800.

Finally found out what the problem was. I must have fried the TIA chip.

I got myself a desoldering gun and removed the TIA chip and added a socket and replaced with another TIA. System works perfectly now.