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Inky

7800 power supply replacement?

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I bought the cable below for my atari 65 XE, and it's been a godsend in getting it working.  If a form of the 7800 proprietary plug could be feasibly reproduced, would something like this be a decent substitute?

 

Looking at my post, I realize this is a dumb question...

https://www.8bitclassics.com/shop/computers/atari-8-bit-computer/atari-xl-xe-usb-power-cable/

 

[attachment=637597:axl-usb-power-cable.jpg]

Edited by Inky

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My only concern with something like this, is that consoles like the 5200, 2600 and 7800 actually require a higher voltage on the input in order for the voltage regulator to actually kick in. When I was a kid and scaring my parents taking stuff apart and mixing components from different old electronics together... I had a universal power supply from Radio shack that I used on my 2600. One day I decided to move the voltage slider down instead of up from the 9 volt setting. I believe the next setting down was either 7.5v or 6v. Anyway, as soon as I moved it down one notch, it was still working but all the colors were crazy in the games. That was when I learned that VRs require a certain amount of input voltage in order to do their job properly.

 

So if you are only provide +5 to the 7800, that might not be enough voltage to kick the VR into action and hence it won't work or could work in very strange ways. In a case like this, it would be best to remove the internal VR entirely and then bridge everything so that the input voltage from the power plug is going straight to the system but you would want to add some protection in there just in case.

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My only concern with something like this, is that consoles like the 5200, 2600 and 7800 actually require a higher voltage on the input in order for the voltage regulator to actually kick in. When I was a kid and scaring my parents taking stuff apart and mixing components from different old electronics together... I had a universal power supply from Radio shack that I used on my 2600. One day I decided to move the voltage slider down instead of up from the 9 volt setting. I believe the next setting down was either 7.5v or 6v. Anyway, as soon as I moved it down one notch, it was still working but all the colors were crazy in the games. That was when I learned that VRs require a certain amount of input voltage in order to do their job properly.

 

So if you are only provide +5 to the 7800, that might not be enough voltage to kick the VR into action and hence it won't work or could work in very strange ways. In a case like this, it would be best to remove the internal VR entirely and then bridge everything so that the input voltage from the power plug is going straight to the system but you would want to add some protection in there just in case.

 

I kinda knew there would be something more needed, as I am a dummy, but I know things are generally not as easy as they seem to be.

Heh, once I had a 2600, but the original power supply went out, and the replacement had a "breakaway" plug portion that uncoupled the wire if someone were to trip on it.  Lo and behold, a friend tripped on the cord, the cord uncoupled, and he reversed the polarity by accident when he recoupled the plug, and my 2600 went bye bye!

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Ive attempted to used 12V supply on 2600 and 7800's before and this caused some strange results on the consoles.  Which is kinda stage as regulators usually are fairly forgiving on larger voltages being used.

 

A 5V input shouldn't work either and might actually cause damage if attempted for a length of time, as the components are powered but (as a result) are attempting to draw more current with the too low a voltage.

 

Ive seen panel meters and digital display go crazy with too low a voltage and with some irretrievable damage in some cases. 

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Ive attempted to used 12V supply on 2600 and 7800's before and this caused some strange results on the consoles.  Which is kinda stage as regulators usually are fairly forgiving on larger voltages being used.

 

A 5V input shouldn't work either and might actually cause damage if attempted for a length of time, as the components are powered but (as a result) are attempting to draw more current with the too low a voltage.

 

Ive seen panel meters and digital display go crazy with too low a voltage and with some irretrievable damage in some cases. 

12v shouldn't be an issue unless that was the actual input voltage you had with a load on it? My 7800s supplies test out at about 12 - 14v without a load in most cases. They drop down to about 10v on the input once plugged in with a load. 12v should be fine and if anything would just make the VR run hotter to dissipate that extra voltage off it I would think but shouldn't behave any differently. I don't know the exact specs on the original VRs but most of them today can handle at least to 15v input and some even more depending.

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yeah - bit weird, i powered up a 2600Jr and a woody 4 switcher last week with a 2amp 12VDC PSU and neither would behave despite being a brand new PSU. (wasnt a charger or anything like that - proper PSU)   7800 might be ok but i do recall this being an issue before.

 

Ive always been ok with 9V however on any of the TIA based consoles.

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On your XE the voltage regulator was most likely in the external power brick. So the input is looking for a steady 5v. You can really use anything that supplies a steady 5v, which USB does. But on the Atari home consoles the regulator was built into the console itself.

Generally speaking 7805s require 2-2.5v over the output 5v. So if you have a power supply that can provide a steady 7.5v, in theory you can use it and generate minimal heat with the regulator.

Of course you could remove the 7805, bridge/jumper the input and output holes on the PCB and then feed 5v in to the console. As long as the supply you are using has enough amperage. Edited by nick3092

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USB is limited to 5V, so no luck here. Youd probably have to rewire the internals of the 7800 to connect the USB power input directly, bypassing the voltage regulator.

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USB is limited to 5V, so no luck here. Youd probably have to rewire the internals of the 7800 to connect the USB power input directly, bypassing the voltage regulator.

That's still not good enough, since the color delay expects at least 8V.

 

If you employ a USB 3.0 communication chip, you can convince the USB source to increase the output voltage up to 20V.  Alternatively, you can use a DC-DC buck converter to reach higher voltages.  I have a switchable 9V or 12V USB-powered supply that does this.  It can run a 7800 with no problems.

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Best Electronics sells a modern PSU with an improved quality plug that fits the original receptacle at a rather reasonable price.

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Best Electronics sells a modern PSU with an improved quality plug that fits the original receptacle at a rather reasonable price.

 

My plan is to get one of these at some point.

I find it odd that an Atari 8 bit computer can work on a ordinary smart phone USB charger, but the consoles can't.

Again, I'm ignorant on all of this.

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I find it odd that an Atari 8 bit computer can work on a ordinary smart phone USB charger, but the consoles can't.

 

As I also learned from one of the above posts, the Atari 8-bit computer is content with 5V while the 7800 needs more for its graphics chip, and normal USB charges don't provide more than 5V.

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Another thing I would add is that using a modern PSU can introduce quite a bit of noise. I run my A8's with Raspberry Pi PSUs, but straight in they are noisy buggers due to a distinct lack of filtering in the A8's themselves (it was probably in the original PSU). I ended up making a little filter box with caps in it with a modern DC jack on one end and the A8 plug on the other. That does the job nicely. I suppose that's sort of what your cable is in essence in the original post, just smoooother ;) My 7800s I've put a DC jack on and run with some big Uniross PSUs. They work just fine.

Edited by juansolo

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Another thing I would add is that using a modern PSU can introduce quite a bit of noise. I run my A8's with Raspberry Pi PSUs, but straight in they are noisy buggers due to a distinct lack of filtering in the A8's themselves (it was probably in the original PSU). I ended up making a little filter box with caps in it with a modern DC jack on one end and the A8 plug on the other. That does the job nicely. I suppose that's sort of what your cable is in essence in the original post, just smoooother ;) My 7800s I've put a DC jack on and run with some big Uniross PSUs. They work just fine.

 

Also interesting to note that I've installed quite a few DC-DC switching regulators in 7800s and haven't experienced any additional noise on the video or audio in the process. I've also used Genesis PSUs and similar to power 7800s when needed. Naturally that requires either changing out the original DC input jack or adding an additional input jack in parallel to the original so you can use either or.

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