Macross_VF1 Posted December 9, 2018 Share Posted December 9, 2018 I fairly recently got my hands on a 7800 intended for the scrap heap. The power supply plug was in somewhat bad shape and the power jack was broken off. When I opened it up I discovered that the soldering points for the power jack was almost completely ruined, as you can see below. However with some careful consideration I managed to find a work around, fitted a new power plug and jack, and got it to power on.However I got nothing but a black screen and some humming/buzzing. Also, I found it strange that the plug wasn't a standard RF jack, but rather the same type found for connecting a monitor to an Atari ST computer. Curious that I am, I decided to open it up further and well, as you can see in the second picture, someone has been a busy little bugger. It has certainly been heavily modified during its lifetime. Still, this brings me no closer to a solution. Anyone know what might be wrong with the system or is it a lost cause? Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 9, 2018 Share Posted December 9, 2018 That is a pal RGB 7800. Mitch 3 Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 9, 2018 Author Share Posted December 9, 2018 (edited) So... it's like this from the factory then? But it's looks so shoddy! Still, I need help in getting it to work again. Edited December 9, 2018 by Macross_VF1 Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 10, 2018 Share Posted December 10, 2018 Do you have the 13 pin din to scart cable? Mitch Quote Link to comment Share on other sites More sharing options...
Shawn Posted December 10, 2018 Share Posted December 10, 2018 So... it's like this from the factory then? But it's looks so shoddy! Still, I need help in getting it to work again. Yep, those are legit Atari pcbs. I agree the work is pretty rough. Never thought I'd see Atari using hot glue on a retail product to secure the power jack like that! Quote Link to comment Share on other sites More sharing options...
+slx Posted December 10, 2018 Share Posted December 10, 2018 Its a French unit, they had mandatory SCART. It should work with an ST to SCART cable (or ST to RGB), maybe also with an SC1224, but those are rare, too. IIRC correctly the ST cables have a resistor on one line which the 7800 doesnt need for optimum picture quality. The power plug might be a DIY fix and you might want to change it for a more common plug when you have to replace it anyway. Id be interested to know whether your unit shows color for 7800 carts. Mine doesnt. 2 Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 10, 2018 Author Share Posted December 10, 2018 Its a French unit, they had mandatory SCART. It should work with an ST to SCART cable (or ST to RGB), maybe also with an SC1224, but those are rare, too. IIRC correctly the ST cables have a resistor on one line which the 7800 doesnt need for optimum picture quality. The power plug might be a DIY fix and you might want to change it for a more common plug when you have to replace it anyway. Id be interested to know whether your unit shows color for 7800 carts. Mine doesnt. Interesting, I had no idea that it was French. Sacre bleu and all that. Now it does 'work' with an Atari ST scart cable as I have one of those lying around, but as I write above, while it powers on (and no sign of the magical blue smoke) I only get a black screen and some background noise. What might be the problem? Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 10, 2018 Share Posted December 10, 2018 Are you trying it with a cart or the builtin Asteroids game? Mitch Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 10, 2018 Author Share Posted December 10, 2018 Both, though to be fair only 2600 carts. I've never actually owned a 7800 cart. Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 11, 2018 Share Posted December 11, 2018 Do you have much soldering experience? Mitch Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 11, 2018 Author Share Posted December 11, 2018 I am decent with a soldering iron so yeah, I know what I'm doing. All I need to know is what to do, what to solder or what to test. Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 11, 2018 Share Posted December 11, 2018 I would start with checking voltages. Make sure the voltage regulator is putting out a steady 5 volts. If you a spare tia chip you could try swapping that out next. Mitch Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 12, 2018 Author Share Posted December 12, 2018 Voltage from the PSU is about 13.5V but under load it drops to about 10.5V which is rather typical of this type of old style PSU. The voltage regulator then does its' job and converts it to around 5V as intended so that's certainly not the problem. I've checked the chips and not one of them seem to become abnormally hot when the power is on. Is there some kind of OS in this machine or is everything directly hardwired? Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 12, 2018 Share Posted December 12, 2018 There is a limited os chip. I don't recall offhand where it is on that board. I would have to pull one apart and check it. Mitch Quote Link to comment Share on other sites More sharing options...
Lynxpro Posted December 13, 2018 Share Posted December 13, 2018 Would it be difficult to clone that SCART board? Is it an Atari Inc or Atari Corp design? And does it export real RGB? Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 13, 2018 Author Share Posted December 13, 2018 It does say Atari on the extra boards so it does seem like a legit design. As for real RGB, well I can't tell, though I'm certain there are ways to find out. Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 14, 2018 Share Posted December 14, 2018 It takes composite video off of the 7800 Maria and TIA chips and splits it out to RGB. So not really a true RGB output. Mitch 1 Quote Link to comment Share on other sites More sharing options...
fluxit Posted December 14, 2018 Share Posted December 14, 2018 Is the result typically better than just outputting composite or s-video over SCART? Quote Link to comment Share on other sites More sharing options...
+SmittyB Posted December 14, 2018 Share Posted December 14, 2018 It should certainly be better than the standard RF but my guess is that a modern video modification will output a cleaner signal given there's a lot of extra processing going on to turn it into an RGB signal here coupled with Atari's world famous quality control. 1 Quote Link to comment Share on other sites More sharing options...
Lynxpro Posted December 15, 2018 Share Posted December 15, 2018 It should certainly be better than the standard RF but my guess is that a modern video modification will output a cleaner signal given there's a lot of extra processing going on to turn it into an RGB signal here coupled with Atari's world famous quality control. Hey now, Atari Inc's quality control was far different than the later Atari Corp's quality control. This SCART board could've been developed by Atari Inc. And I know one of the last things Dan Kramer worked on before he left the Tramielian Occupation was finishing up the SECAM versions of the Atari XL computers. And he left before 1985... If this is a decent board, I'm surprised nobody has cloned it. I'd take SCART over Composite or SVideo. Then again, a lot of 7800 mod boards come from the States and SCART wasn't popular here plus not too many enthusiasts here own French 7800s... Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 15, 2018 Author Share Posted December 15, 2018 So from what you guys are discussing, this console might actually have value to others, if for no other reason than learning how to reverse engineer the parts? Neat! I suppose if I can't get it to work, I can consider donating the unit to someone with the know-how to clone the extra boards.That said, if at all possible I would like to get it operational. Since I do seem to get the appropriate power, but it doesn't boot up any games, should I consider replacing some of the chips, possibly the ones that hold the OS? Quote Link to comment Share on other sites More sharing options...
+Mitch Posted December 15, 2018 Share Posted December 15, 2018 The OS chip is an easy way to start. You can burn the ROM to an EPROM and it is a straight swap. If there is room for a socket under the daughter boards then you may considering putting one in to make it easier to swap in the future. The OS chip should be labeled C300558. You can burn it to a 27C128 EPROM. If you look at this pic: http://www.atari7800.org/boardscans/C300633.jpg you can see it in the middle of the bottom row of chips. This is the same board that you have minus the daughter boards. ROM file is here: http://www.atari7800.org/bin/pal/a7800p.zip Mitch Quote Link to comment Share on other sites More sharing options...
Macross_VF1 Posted December 16, 2018 Author Share Posted December 16, 2018 I'll try it though it will have to be some time after Christmas. Anyway, thanks for the help. Quote Link to comment Share on other sites More sharing options...
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