+batari Posted October 25, 2014 Share Posted October 25, 2014 I picked up a 7800 on eBay for testing things. The usual "as is, not tested" deal and I took a chance. 2600 mode works perfectly, but 7800 mode does not work. I've cleaned everything, reflowed solder all over the board and reseated the one socketed chip (Maria) and nothing made any difference. This probably means the TIA, RIOT, 6502, the BIOS and all of the logic chips are good. This leaves just MARIA and the 6116 RAM chips. 99% of the time, when you insert a 7800 cart, the unit shows garbage when you turn it on. However, occasionally I get this screen (note the ATARI logo at the top, so BIOS is at least attempting to run, sort of): What do you think, MARIA or RAM? Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted October 25, 2014 Share Posted October 25, 2014 That kind of screen garbage looks like what was going on with my 7800 until I opened it up a couple weeks ago and tightened up the cart slots. The pins on the ends, extending beyond the standard 2600 pins, were key. Once I cleaned and increased the spring tension on all the pins, the problem went away. Interestingly, I had NO problems with any 2600 carts at all. But after I did my little tightening procedure, all my 7800 games are working okay again. I don't know if the pins on the ends are more susceptible to loosening, or if the 7800-specific signals are more susceptible to marginal connection to the cart. Might be worth a try to tighten up all the pins before you go replacing chips - FWIW, I used an ordinary toothpick, worked up behind each pin, to bend them gently inwards and tighten things up. Quote Link to comment Share on other sites More sharing options...
FireTiger Posted October 30, 2014 Share Posted October 30, 2014 I have one that only plays 2600 games but not 7800 games I wonder... Quote Link to comment Share on other sites More sharing options...
Lynxpro Posted October 31, 2014 Share Posted October 31, 2014 Has anyone ever installed replacement SRAM in their 7800 that was more than 4K? I'm curious whether that would cause more of the game code to load into there like a buffer; obviously, for a home brew or hack to truly take advantage of it, it would have to be mapped similar to the added RAM on the XBoard and XM... Quote Link to comment Share on other sites More sharing options...
Rybags Posted October 31, 2014 Share Posted October 31, 2014 Games usually run direct from Rom, there's no reason to copy code to Ram other than if it needs to be self-modifying. Whether a larger Ram would just slip into the memory map, kind of doubtful, would need to look at schematics and tech info. Regardless, it's unlikely any game would bother testing for more Ram than it was designed for, so beyond being a development aid it wouldn't be all that useful. Quote Link to comment Share on other sites More sharing options...
Andromeda Stardust Posted October 31, 2014 Share Posted October 31, 2014 (edited) I picked up a 7800 on eBay for testing things. The usual "as is, not tested" deal and I took a chance. 2600 mode works perfectly, but 7800 mode does not work. I've cleaned everything, reflowed solder all over the board and reseated the one socketed chip (Maria) and nothing made any difference. This probably means the TIA, RIOT, 6502, the BIOS and all of the logic chips are good. This leaves just MARIA and the 6116 RAM chips. 99% of the time, when you insert a 7800 cart, the unit shows garbage when you turn it on. However, occasionally I get this screen (note the ATARI logo at the top, so BIOS is at least attempting to run, sort of): badatari.png What do you think, MARIA or RAM? Your screenshot reminds me of an incident at my friends house as a kid growing up. He was playing an NES game, and the graphics corrupted across the entire screen. He told me that's what the inside of the cartridge looked like. Never having seen the internals before, I took his word for it there was some kind of magic that magnified the circuits and displayed them on the TV. Either way he got it working again after blowing and reseating the cartridge. Your screenshot reminds me of that moment from my childhood. Hope you get it working. If you have an additional 7800, you can very easily swap the socketed Maria chips and will know instantly whether it is suspect or something else entirely. Edited October 31, 2014 by stardust4ever Quote Link to comment Share on other sites More sharing options...
Rybags Posted October 31, 2014 Share Posted October 31, 2014 The Rams on 7800 use CS signals generated from Maria (one for each 2K chip) - I should think to add extra internal Ram that extra select logic would be needed. Quote Link to comment Share on other sites More sharing options...
Lynxpro Posted October 31, 2014 Share Posted October 31, 2014 The Rams on 7800 use CS signals generated from Maria (one for each 2K chip) - I should think to add extra internal Ram that extra select logic would be needed. So you don't think the MARIA would just grab hold of any extra RAM on its own? Wow, that's no fun. Quote Link to comment Share on other sites More sharing options...
Rybags Posted October 31, 2014 Share Posted October 31, 2014 Not really. It's a fixed config base system (disregarding 2600 modeswitch) so no need for Ram test and such like computers where it might be installed incrementally. Having Maria take care of that Ram select logic eliminates needing to do it elsewhere - again since it's a fixed internal config it makes sense to do such things as cheap/simple as possible, but does make it a bit harder for doing modifications later on. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted October 31, 2014 Share Posted October 31, 2014 So did Batari ever post again and tell us what the problem was with this machine? Quote Link to comment Share on other sites More sharing options...
omf Posted November 10, 2014 Share Posted November 10, 2014 "as is, not tested" this is eBay terms for tested and does not work its an easy get out clause imho for making cash out of dead hardware Quote Link to comment Share on other sites More sharing options...
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