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Atari 7800 power replacement


DarthLister

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Has anyone tried replacing the 7800 power supply and power connector? I replaced mine with a smaller 9v 1A supply and a modern connector and I'm getting what is surely elec interference in bands of interference that scrolls up the screen.  I replaced the caps, but that actually made it worse. Any ideas?

 

Thanks,

          Rich

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6 hours ago, DarthLister said:

Has anyone tried replacing the 7800 power supply and power connector? I replaced mine with a smaller 9v 1A supply and a modern connector and I'm getting what is surely elec interference in bands of interference that scrolls up the screen.  I replaced the caps, but that actually made it worse. Any ideas?

 

Thanks,

          Rich

The caps aren’t the cause of the noise in your system - it’s the modern switching-mode power supplies used today. The produce lots of high-frequency noise that affects vintage systems pretty badly. You can try to find some ferrite beads (Amazon or eBay) to snap over and around the power the cord and possibly your video output from the 7800, but the real solution is to go back to the original Atari PSU and just replace the connector on the pigtail. If you can’t do that, you’ll have to experiment until you find a better, less noisy PSU.

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Not sure if Best has replacement connectors for the main board, but I have made up a few wire harnesses that would allow you to plug into the 7800's power port, and then provide you with a more common barrel jack on the end. But I made them up wired specifically for using with a Genesis, SMS, or Jaguar power supplies due the polarity. Not a perfect replacement, but great if you have other power supplies that can be used and don't have a spare 7800 one handy.

 

Best does sell a replacement power supply for the 7800 though. I've not purchased one myself, but they are spec'd proper and those that have bought them, say they work really well.

 

BTW...I tested my wire harnesses using a modern day switching power supply that is sold as a Genesis or Jaguar (But also works well for my Roland modules) power supply from Console5 for about $10.

 

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1 hour ago, -^CrossBow^- said:

BTW...I tested my wire harnesses using a modern day switching power supply that is sold as a Genesis or Jaguar (But also works well for my Roland modules) power supply from Console5 for about $10.

Good to know, because indeed, all modern switch-mode PSU’s are *not* the same.

 

I have a cute little 9VDC supply that came in a giant Elegoo-branded Arduino kit I bought several years ago. When I was messing with 555 timer circuits for fun a few months back, I powered my little breadboard power module with it. This module is basically a few SMT-based voltage regulators that you can plug in a 5VDC - 12VDC source to give your breadboard 3.3VDC and/or 5VDC. Using the Elegoo PSU, my scope showed beautiful, clean signals out of the 555 chip. I bought a second 9VDC generic “Arduino power supply” and tried the 555 circuit with that and my scope was filled up with all kinds of noise and crap. I experimented with several different values of ceramic and electrolytic caps on the power rails of my breadboard to clean up the noise in that PSU but although I could reduce it, I couldn’t get rid of it entirely.

 

Similarly, when I bought a 4-port 5200 a few years ago, the original PSU died several months later when I used it to diagnose problems with a second 4-port that evidently has a shorting problem on the motherboard. I replaced it with a 12VDC supply from an external hard drive that had died. That PSU is super-quiet, noise-wise, and works great powering my 5200. When I got a 2-port 5200, I tried a second 12VDC supply I had around (from an old router), and there was just all kinds of noise in the picture - really terrible. 

 

All of the above are modern, switching PSUs but they are decidedly not equal. 

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Yes, I have other similar unknown brand PSUs laying around and noticed that my roland modules are especially sensitive to the PSUs I use on them. In fact, most modern switching supplies tend to put a very audible hum on them and due to that I was using spare Genesis PSUs I had laying around to power them initially since those provided clean power without adding anything to the modules. Eventually, I got around to buying actual Roland branded replacement switching PSUs for them that work great. But having said that I have my Edirol SD-20 powered using one of the $10 Genesis replacement PSUs from console5 without any issues and I don't have any reason to not believe Console5 when they state they have done their testing to ensure these are noise free supplies. Same with their 2600 replacement supplies as well although, those do cost a tiny bit more.

 

Now that I think about it, I probably should have changed the polarity on my adapter harness so that you could actually use a 5200 PSU to power a 7800 if you wanted but I figure a Genesis or same specc'd PSU is easier to find for a cheap price these days?

 

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2 hours ago, edladdin said:

Mouser has an old school non-switching 9v, 1A Power supply with a modern barrel plug:

Power Supply

 

Here’s a link to a matching jack:

2.1x5.5mm panel mount jack

 

Edit:  Using the link feature.

 

Traid make good supplies. I use their 5v model as a replacement for earlier Neo-Geo consoles and it works excellent for that!

 

Here is an earlier one of the adapters I made up but the prices for the wire harnesses and barrel jacks make these a bit too expensive to offer cheaply to people for the time being.

 

Genesis_to_7800_PwrAdpt.thumb.jpg.11aeb6d6880d9680a41e07d3bd10bb42.jpg

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