Atari 2.6 DOM vs 4.2 DOM Diagnostic Eprom Chips

[Scooter83]

I got a bunch of Eproms in the mail from an ex Atari programmer. I have 2 2.6 Diagnostic Eprom that I plugged into my eprom cart and they fired right up . However the 8 to 12 4.2 Diagnostic Eprom chips they dont fire up. Any ideas to why? Is one a 4k or a 8k that im not aware of ? The board reads all my other eproms i have laying around. ( Pitfall , Night Driver, Outlaw, River Raid ) but for some reason my 4.2 DOM diagnostic chips wont read. Any thoughts?

[alex_79]

Can you read the markings on the eprom chip?
The 4.2 DOM eprom shown on atariprotos is a 2716 (16 kbits - 2 kbytes).
Some of the game you mentioned are 4k, some 2k. What type of eprom are they? (2k games work on 4k eprom if they're copied twice on it). Do your eprom cart accept both 4k and 2k eproms? In that case there should be a switch or a jumper to select betwen the two.
Also note that the 2.6 version requires two test plugs in the controller ports to work correctly, but it still display an image without them. Maybe the 4.2 doesn't display anything without the test plugs. Instructions for the 2.6 version can be found in the 2600 service manual which is available in several places on-line, but I found nothing about the 4.2. If you have access to an eprom programmer or can send the eproms to someone who has one, a dump of the rom might shed some light.

Edited October 6, 2016 by alex_79