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hoserama99

Atari 800 12V DC adapter problem

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Hi all, I'm not an electronics expert by any stretch so I'm hoping for some guidance.

 

If someone plugged a 12V *DC* adapter into a beige Atari 800, what are the odds of lasting damage to the computer? I'm talking to a seller who said they plugged it in, saw the red light briefly turn on then nothing.

 

Going on just that little bit of info, I'm trying to figure out if it's worth my while to take a gamble that the computer is still OK.

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More than likely the damage will be limited to the power supply section in the Atari's case. I would look for a decent discount and repair or replace the power board in the Atari...

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Believe it or not, it might actually be okay if they didn't leave it on very long. Of course, the seller could be lying. 

 

In my experience, it's worse to plug an AC power supply into something expecting DC - sparks and hilarity can ensue. Don't ask me how I know that ... 🙄 

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Yeah - usually passing DC through an AC device will create some heat, but not do immediate damage.  The DC passes through half of the full-wave rectifier creating heat in those 2 diodes, but that should really be about it.

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Thanks guys - I appreciate the risk analysis!

 

I actually advised the seller to plug it in and see if it powered up. It's only when he told me the result that I looked closer at the picture of the power adapter and realized it was completely wrong for the A800.

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8 minutes ago, Stephen said:

Yeah - usually passing DC through an AC device will create some heat, but not do immediate damage.  The DC passes through half of the full-wave rectifier creating heat in those 2 diodes, but that should really be about it.

correct, it heats up and handles full duty and magnitudes more current (more than twice) as it has no waveform and only passes through half the rectifier. That normally cooks the rectifiers or diodes...

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1 hour ago, hoserama99 said:

Thanks guys - I appreciate the risk analysis!

 

I actually advised the seller to plug it in and see if it powered up. It's only when he told me the result that I looked closer at the picture of the power adapter and realized it was completely wrong for the A800. 

 

Yes this is why it's not good to ask a seller to power on an old computer or device.  If the seller doesn't know the A8 platform but says "it powers on I see the light" that's actually a bad thing to me as a buyer. That lowers the value.  He/she could have damaged it at that moment.  Now if the auction photos show the correct power supply then that's better but never have I seen a seller say "First I verified the correct voltage from the power supply using a volt meter, then tried powering it on." 

 

Much more important is to ask the seller to use a lot of bubble wrap or excess padding to keep it from breaking in transit. Every. Single. Time.  Sometimes I even offer, before they ship it, extra shipping compensation if it arrives safely. This is especially important for 800's which have such fragile cases with a heavy block inside. The very thought of an 800 breaking in shipping is worth preventing with an offer of an extra $10 to $20 to the seller if it arrives safely and was packaged well.

 

 

Edited by Sugarland
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Those are all great points. If I'm being honest with myself, I think there's a chance I also would have attempted to power it on with the adapter that was offered, without first verifying it. I'll definitely ask for extra bubble wrap and hope for the best. I've never owned an 800 so I'm not fully aware of how heavy or fragile it is. I've got a 400 that seems pretty solid and kinda light, so I assumed the 800 was similar.

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1 hour ago, hoserama99 said:

Those are all great points. If I'm being honest with myself, I think there's a chance I also would have attempted to power it on with the adapter that was offered, without first verifying it. I'll definitely ask for extra bubble wrap and hope for the best. I've never owned an 800 so I'm not fully aware of how heavy or fragile it is. I've got a 400 that seems pretty solid and kinda light, so I assumed the 800 was similar.

Probably not a danger in your case as the PSU is not the right type anyhow, but always be sure to have the PSU bubble-wrapped separately and secured. I had a 400 case completely smashed beyond repair by a PSU separated from the unit by a few balls of newspaper. That old plastic is brittle and all those large grilles are easy to break and hard if not impossible to glue together. 

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1 hour ago, slx said:

Probably not a danger in your case as the PSU is not the right type anyhow, but always be sure to have the PSU bubble-wrapped separately and secured. I had a 400 case completely smashed beyond repair by a PSU separated from the unit by a few balls of newspaper. That old plastic is brittle and all those large grilles are easy to break and hard if not impossible to glue together. 

Yeah, I actually asked the guy to toss the PSU and ship just the computer to try and be safe. I don't know if I would have considered any of this before this thread so it's been very helpful advice.

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The DC power supply would have been great for perhaps an indus drive, or 5200 etc. depending on the supply block.

Edited by _The Doctor__
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Hope it powers up ok when you use the correct PSU, remember AC power has no +ve/-ve terminal, so if the DC

PSU used connected up the wrong way round, the 5V and 12V regulators would have +ve on the ground terminal

and -ve on the input, also all the electrolytic capacitors would reversed which (if the Caps are old) may damage them.

 

Basically proceed with caution, chances are that the polarity was correct (relatively speaking :))  ) as he said the red

light came on briefly, the red light is from the -5V supply, this part of the circuit needs AC to continue, so with DC

applied you would see the LED light briefly as the in-line capacitor charges.

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2 hours ago, TGB1718 said:

Hope it powers up ok when you use the correct PSU, remember AC power has no +ve/-ve terminal, so if the DC

PSU used connected up the wrong way round, the 5V and 12V regulators would have +ve on the ground terminal

and -ve on the input, also all the electrolytic capacitors would reversed which (if the Caps are old) may damage them.

 

Basically proceed with caution, chances are that the polarity was correct (relatively speaking :))  ) as he said the red

light came on briefly, the red light is from the -5V supply, this part of the circuit needs AC to continue, so with DC

applied you would see the LED light briefly as the in-line capacitor charges.

Looking at the picture of the incorrect adapter, negative was on the "outside" ring and positive was on the "inside" - if you'll pardon my ignorant terminology. :) I believe this means -ve was connected to ground, so hopefully not a complete disaster. I'll definitely take some care powering it up the first time though.

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Consider this: The input changes from +9v to -9v 60 times per second on a normal 800. So, no immediate damage will occur and polarity does not matter. There are voltage doubler circuits in the 800 power supply which will not work with a DC input, but they won't blow up, either.

 

Bob

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either the power block fizzled or something in the power supply fizzled, 12VDC can certainly do damage after a bit, 9vac at 60 hz puts the duty cycle into play where as the 12vdc pegs it at 100 percent and above input. The doubler should have tolerated it.. the rest not so much. So it still stands to reason either the power adapter block died or the 800 lost a couple diodes etc in the internal supply as evidenced by the 800's light going out. It's still more than likely a cheap fix.

 

I didn't catch the current rating on the 12vdc supply block either, so who knows maybe it died, tripped, blew a fuse... hopefully it gracefully went south and didn't spike or hopefully just cut out and didn't do anything silly.

Edited by _The Doctor__

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I'm impressed with what this discussion has sparked, and have enjoyed reading the feedback, positive and negative. I'm glad the subject hasn't been too polarizing. ;)

 

Here's the only pic I have of the incorrect supply. It's 11.5V DC, 1.95 amp. I'll give a final update when the A800 arrives and I've got it confirmed working.

 

 

Screen Shot 2019-06-20 at 1.53.07 PM.png

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part of the fun is to get all the information and then get the grey matter in everyone's skulls active. Tidbits of knowledge, know how, and trivia can help folks learn quite a bit and apply it. Some things might not be applicable in the instance sited but can be used elsewhere. Good times.

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FYI, the final update on this: the computer arrived today and fired right up with the proper AC adapter!

 

The only thing I noticed is that some keys don't register on the first press (or at all) but I haven't done any diagnostics on that, and probably won't have time to look at it further until the weekend. For now I'm going to assume it's unrelated and easily fixed, for no reason other than blind optimism. :)

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Cool, the dc power supply must have popped. and the Atari is fine.

That's wonderful, use the keys a lot, sometimes surface oxidation on the swipes will wipe away...

does the space bar work?

Edited by _The Doctor__

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48 minutes ago, _The Doctor__ said:

That's wonderful, use the keys a lot, sometimes surface oxidation on the swipes will wipe away...

does the space bar work?

Space bar works, yes. Most keys work, but some (about 30-40% of them) require multiple keypresses to register, and some don't seem to register at all (maybe 10%). I'm assuming because some of them require multiple presses that it's (hopefully!) just an issue with dirty contacts either in the keyboard or on the connector, but that's just blind speculation. I did try a quick search of the forums but indexing still isn't complete so I'm not getting any useful hints. I'll ask about the keyboard in a new thread in a few days, after I've had time to do some bare-minimum troubleshooting, if it's still wonky after that.

 

Thanks again all!

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Like I said oxidation, the more you use them the better they should get, light deoxit can make this much better. Be careful to us a key puller and to do so with the plastics warm... the risers in these old keyboards can be quite brittle and crack otherwise if cold and / or pulled on any kind of an angle...

 

one step at a time...

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