7800 works for 7800 games, not for 2600 games.

[homestar92]

I bought a 7800 yesterday and it's only partially working. It works great for 7800 games, but I get no signs of life at all aside from a black screen when I fire up a 2600 cartridge. I tested every cart in my collection (including my harmony cartridge) and only a single one of my 2600 carts shows even a slight sign of activity, which is Moon Patrol. It shows a bunch of garbage on the screen (picture attached). Are there any components on the board used exclusively in 2600 mode where I could start my diagnosis?

[CPUWIZ]

Does it have sound?  If not, the TIA chip is probably broken.

[homestar92]

3 minutes ago, CPUWIZ said:

Does it have sound?  If not, the TIA chip is probably broken.

It does have sound. In fact, I swapped the TIA from my working 2600 and the TIA from the 7800 works in the 2600, and the TIA originally from the 2600 results in no change in the 7800

[CPUWIZ]

Ok, cool.  I am rather busy, so I am going to move this for you to the 7800 forum, as I know a bunch of engineers are reading it over this forum and may be able to help you out quicker.

 

 

[alex_79]

Maybe a bad RIOT ram?

[homestar92]

5 hours ago, alex_79 said:

Maybe a bad RIOT ram?

Pulled the RIOT chip and swapped it with the one from my 2600 and it worked!

Is there any difference between the chip in the 2600 and the 7800 and is there any problem in using it like that while I wait on a replacement?

[alex_79]

The chips are the same.

I think 7800 games only use the RIOT to read the joysticks and console switches, and not for the ram, so they'll probably run fine with the bad chip.

Edited March 27, 2022 by alex_79

[johannesmutlu]

On 3/25/2022 at 4:58 PM, CPUWIZ said:

Does it have sound?  If not, the TIA chip is probably broken.

 

On 3/27/2022 at 9:57 PM, alex_79 said:

The chips are the same.

I think 7800 games only use the RIOT to read the joysticks and console switches, and not for the ram, so they'll probably run fine with the bad chip.

I wonder why atari didn’t added a pokey chip in their atari 7800 and instead just rely on the pokey chip externally from supported games, what atari should,ve done is adding the pokey soundchip to run alongside the mario video chip in atari 7800 mode but switch them off in atari 2600 mode, also i wonder if the tia chip could run alongside the maria chip in atari 7800 mode because if so then you could have an extra background and sprite layer on top of the maria chip,if not then atari should,ve done that too to make the most off out their system.