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Android8675

800 + 5200PSU = AHHHHHH! Nonononononooooo!

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So.... I accidentally powered on my 800 with my 11.5v, 5200 ps, Quickly realizing my mistake I found the correct adapter and when I powered it on, nothing. I re-seated my ROM/RAM cards and now the text on the computer looks like this...20307_10151194072113171_1776632903_n.jpg

 

What did I hose? Is there a util I can use to diagnose the problem?

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I'm surprised it did any damage. The first thing that happens to the incoming AC power is rectification to DC.

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Well then maybe my old a8 just gave out at that moment. I haven't run the system in a few months. been sitting next to me since. (right before Incognito too :_( ).

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Here's the schematic of the 800's power section. You can check to make sure you're getting the proper voltages out of it now.

 

The 5200 supply is tip positive, so it would have powered up without the -5v rail (and with a droopy 12v rail). I believe the -5v only goes to RAM, so it's possible the RAM was damaged by being semi-powered. It works enough to show the MEMO PAD. I'd see if games carts work on it. Also, try it with one RAM card at a time.

800pwr.pdf

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Couldn't you get that sort of thing if the 4050 luma buffer IC was faulty?

 

That's an OTS part - you can pick up for maybe a buck fifty from most electronics places.

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Couldn't you get that sort of thing if the 4050 luma buffer IC was faulty?

 

That's an OTS part - you can pick up for maybe a buck fifty from most electronics places.

Hmm.. now that you mention it the symptom appears to be that if the text graphics are on for more than a few pixels, it stays on too long. Short segments seem fine.

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Here's the schematic of the 800's power section. You can check to make sure you're getting the proper voltages out of it now.

 

The 5200 supply is tip positive, so it would have powered up without the -5v rail (and with a droopy 12v rail). I believe the -5v only goes to RAM, so it's possible the RAM was damaged by being semi-powered. It works enough to show the MEMO PAD. I'd see if games carts work on it. Also, try it with one RAM card at a time.

 

Thanks for the suggestion, I pulled all but one RAM and tried each one, seemed to have the same problem. Will double check in a moment.

 

Oddly I came in when the Atari was in the screen save color change thingy and the characters looked OK. When I pressed a key they returned to how they looked in the original photo. Was odd.

 

Thanks again,

-A.

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Couldn't you get that sort of thing if the 4050 luma buffer IC was faulty?

 

That's an OTS part - you can pick up for maybe a buck fifty from most electronics places.

 

I'll keep it in mind for when I've exhausted all other options. Thanks!

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Oddly I came in when the Atari was in the screen save color change thingy and the characters looked OK. When I pressed a key they returned to how they looked in the original photo. Was odd.

 

That's a good clue right there. The thingy is called Attract Mode and one thing it does is to zero the high luma bit. So if the smearing only happens when the high bit is on, then that lends cred to Rybags' diagnosis. Either the 4050 or the GTIA itself is bad, or maybe one of the video amp transistor circuits saturating and blooming?

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So must be some problem with the high luma bit.

 

Could be GTIA, the 4050 IC or some stage of the video circuit. It's as if it's holding too long when there's more than 2 pixels of bright display.

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So must be some problem with the high luma bit.

 

Could be GTIA, the 4050 IC or some stage of the video circuit. It's as if it's holding too long when there's more than 2 pixels of bright display.

Easy to fix? Never popped open this 800 save for the rom/ram slots. I assume the GTIA I'd have to find a replacement from another Atari? Can I pull a GTIA off a 800XL mobo and use it in the 800?

 

The other IC, is this something I could pick up at Digi-Key or somewhere?

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The bit is being picked only in specific character set rows. The only chip that knows what row is output is the ROM, isn't it? Did you try the ROM board?

 

Bob

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I still think it's where there's more than 2 bright pixels adjacent, check the "-" before "memo pad", it's about 2 pixels longer than normal. Plus, he's proven it to look normal if you darken the text (ref #13)

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The bit is being picked only in specific character set rows. The only chip that knows what row is output is the ROM, isn't it? Did you try the ROM board?

 

Bob

 

Not sure how to troubleshoot the ROM board, I don't have another one to try out. I'm getting an incognito soon, and I think that replaces the ROM board so I guess if it does turn out to be that I'll have a solution in a few weeks.

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You might want to make sure that your 800 is 100% before you add anything to the hardware. No way to know what the failure might look like if you put in an incognito in there.

 

Bob

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You might want to make sure that your 800 is 100% before you add anything to the hardware. No way to know what the failure might look like if you put in an incognito in there.

 

Bob

 

That's good advice. Just 'swapping out' ICs or boards isn't always a good approach. If something has failed then there may be a good reason for it - power rails should be the first thing you check for example.

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That's good advice. Just 'swapping out' ICs or boards isn't always a good approach. If something has failed then there may be a good reason for it - power rails should be the first thing you check for example.

 

ok so what do I want to try first the ROM board, or the 4050 ic? Can someone link me to the IC, I tried to just find it an am not really sure what a 4050ic is or where to find one.

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If I had to guess at this point, I'd say it's a problem in the video amplifier circuit. When it's driven to a certain point, a transistor isn't shutting off correctly.

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ok so what do I want to try first the ROM board, or the 4050 ic? Can someone link me to the IC, I tried to just find it an am not really sure what a 4050ic is or where to find one.

The CD4050 is a non-inverting hex buffer, there are threads about A/V mods/upgrades for the 2600/Atari 8-bits that recommend using the CD74HC4050 instead. The lower propagation delay of this chip is supposed to reduce color bleed.

 

http://www.futurlec.com/4000Series/CD4050.shtml

http://www.ti.com/product/cd74hc4050

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So bob1200xl sent me a CPU and a ROM board for my ailing 800. I replaced both (first just the rom board, then the cpu, then both), no change. So I got some contacts to send me some CD74HC4050E samples, I might try that next unless other suggestions can be given in the meantime.

 

Thanks for the help all,

-A.

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