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Atari 800 (not XL) blank screen

falter

falter

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Jan 22, 2011
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Location
Vancouver, BC
About 17 years ago I got a bunch of computers from a Vancouver place called Cal's Computer Warehouse. They had a little museum set up at the front of their store which they eventually shut down, and I managed to swoop in as the last of it was being cleared out. Among the various machines was an Atari 800 that I got sans power supply. Amazingly, I never bothered to try and getting it running until last week, when I finally got my hands on a power supply. Anyway, tonight I fired it up.. and.. yeah. Zip. Just a brown or beige screen. Reset sometimes changes it from one to the other. That's it.

I have two carts.. QIX and BASIC.. neither produce any change. I also tried removing/rotating RAM cards.. this also did nothing. So I'm wondering if others have hit this predicament before me. Wouldn't mind seeing what this thing can do.
 
Thanks! So even the Memopad is not coming up when carts are out of the machine. Seems like I have a more serious issue here. Wonder if my ROM card is bad.
 
What are you using for a display? If it's the RF cable connected to a TV, work the channel selection switch on the Atari back and forth a few times. That really switch likes to be spotty. If you have the computer connected to a composite display, make sure you have a compatible cable. Many other similar computers of the time used the same DIN connector, but wired things differently.
 
It's to a TV. I get a solid color display.. sort of a beige/rose colour. It doesn't fit what they describe in the flowcharts... unless that's what they consider to be 'grey'.
 
Well, I've made a bit of progress. I purchased a replacement ROM board, and after fiddling I do periodically get Memopad. I was also able to get BASIC up and run a short program before it froze. But it is still erratic.. sometimes nothing comes up onscreen at all, or sometimes it'll come up and then throw garbage out. I feel like I'm battling a RAM problem. I'm looking around for a way to make a diagnostic disk or get a diagnostic program onto the 800 to test more fully.
 
Nice to see you made some progress.

Are the voltages on the DRAM chips within specs ? (+5Volts, +12Volts and -5Volts)

These old DRAM chips need all three of them to be present. If not, check the power supply, especially the voltage doubler made with CR2024, CR2025, CR204, CR205 and A201 (12V regulator).

The negative current to generate -5Volts flows through (!) the power LED and is stabilized by CR201 (a 5.1 Volt zenerdiode).

I assume you are using the original Atari (9Volts AC output!) power supply.
 
Yes original PSU.

I have noticed that pressing down firmly on the board results in more reliable operation. I'm thinking either the contacts are not good or the board maybe has some fractures in it.
 
I would pull that puppy completely apart, cleaning all the edge connectors with a soft pencil erasure, and working all the connectors on and off, even pulling out and re-inserting the IC's. There may well be a crack in a circuit board somewhere, but spotty contacts seem much more likely.
 
Yeah that's what I'm thinking. But how do you clean well inside the sockets?? They don't come apart do they?
 
For the IC sockets, I just work the chip out and back in. This has been sufficient for all but the worst cases. Usually if I clean the card edge connectors, then work the card in and out of the socket a few times, that takes care of it. I did have to go a step further with the cartridge slots. I wrapped a very heavy paper shop towel around the contact edge of a cartridge (the board removed from the cartridge case), then wet the towel with isopropyl alcohol and work that combo in and out of the affected slot. It has to be a reusable type of paper towel so that it won't just disintegrate, or a very thin cloth.
 
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