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Replacement adapter for MP 790

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PDXMark Page Icon Posted 2009-11-13 11:03 PM
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Don't have a multimeter, unfortunately. And I'm a bit confused on the polarity of the adapter. There's nothing to indicate the polarity, and no instructions came with it. I've done a bit of searching online to figure it out, but haven't found much direction yet - at least nothing that helps with this adapter.

Rich, the tips have the two prongs, like you said. And at this point, I'm pretty sure I've had the tip on both ways and plugged the adapter into the wall both ways (both prongs are the same size), and I'm still getting no juice. At least the battery is still working, so I haven't damaged it.

I may get time tomorrow to stop by Radio Shack and look at tips. It may just be that the tip is too small. If I can't find something that works, I'll return the adapter....I have a friend working on repairing my old broken 790 adapter, and that may end up being the best option.

Anything else I should check?
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hmascience Page Icon Posted 2009-11-13 11:18 PM
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There should be a mark on the tip (plug, really, since the plug has a tip and a shaft that are the contacts for power) and one on the jack (directly connected to power supply). The mark will mean that the tip (of the plug) is positive or that the tip is negative (and the shaft has the corresponding opposite polarity). To change the polarity, you take the plug off and rotate it 180 degrees.

I think somewhere on this site (or maybe Rich's), there is either a reference to the Radio Shack plug (type C maybe) which will lead you to the actual dimensions or somebody had posted the dimensions. I know I did it with the Fujistu and I know I was in your shoes a few years ago, but I don't remember if I found the Radio Shack dimensions online (and a corresponding NEC reference ... maybe it was an e-bay ad) or I just took my unit down to the store and went through the available plugs (they have a keychain and you just experiment until you get one that works).
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PDXMark Page Icon Posted 2009-11-13 11:52 PM
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Quote
hmascience - 2009-11-13 8:18 PM

There should be a mark on the tip (plug, really, since the plug has a tip and a shaft that are the contacts for power) and one on the jack (directly connected to power supply). The mark will mean that the tip (of the plug) is positive or that the tip is negative (and the shaft has the corresponding opposite polarity). To change the polarity, you take the plug off and rotate it 180 degrees.

I think somewhere on this site (or maybe Rich's), there is either a reference to the Radio Shack plug (type C maybe) which will lead you to the actual dimensions or somebody had posted the dimensions. I know I did it with the Fujistu and I know I was in your shoes a few years ago, but I don't remember if I found the Radio Shack dimensions online (and a corresponding NEC reference ... maybe it was an e-bay ad) or I just took my unit down to the store and went through the available plugs (they have a keychain and you just experiment until you get one that works).


I finally found the marks on the plug....man, they're small. I keep putting off getting bifocals, but if they keep making things so tiny, I may have to reconsider.....So I don't think it's a polarity issue, cause I've had the plug in both ways and it made no difference.

I think I'll take the 790 down to Radio Shack tomorrow along with the adapter and see if they can find a plug/tip that fits better.

Thanks!

FYI, the plug I'm using has "4.0 x 1.7" inscribed on the side, so I assume that's the size.

Edited by PDXMark 2009-11-13 11:56 PM
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PDXMark Page Icon Posted 2009-11-22 10:33 PM
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OK, time for an update....the friend who's been working on my broken adapter returned it to me this morning fully repaired. However, when I plugged it in.....nothing. I know the battery and the unit both work, so I'm guessing there's an issue where the plug connects to the unit......right? Does anyone have experience with this kind of problem? What should I be looking for?

Also, Rich graciously included the AA adapter with the 790, so I have that option. But I've found that AA's don't hold a charge for long, especially if I'm doing any word processing or reading PDFs. Is there a certain type of AA cell that works better, or is any AA just as good? And will rechargable AA's work?
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hmascience Page Icon Posted 2009-11-23 7:28 AM
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Umm, how much do you like your 790 and how are you charging the lithium battery pack (BA14A)? I ended up getting the desktop charger (since the charging circuits on my two MP's gave out). The Li packs are good for 4+ hours for word processing use (original packs). Right now, they are being used by my kids, but I anticipate that a cell replacement/rebuild will be needed soon and I have some 2600 mAH cells to put in (to replace the stock 1700 mAH). You can compare those numbers to "standard" AA batteries. I don't know if NiMH AA rechargables will work, but I also don't think it'd hurt to try. I'd be interested in hearing of any experiences, also.
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PDXMark Page Icon Posted 2009-11-23 1:52 PM
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I may have found a solution. I came across an old post (http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=5698&start=1) saying that NiMH rechargeable AA batteries work in the AA adapter. I went scrounging through surplus supplies at work (we downsized recently and have an overabundance of stuff) and found 25 NiMH AA rechargeable batteries (they had been dumped in with spent alkaline AAs) and a universal charger. The first 4 batteries are charging now. I don't know how many charges these batteries have had, but I figure that out of 25 I should be able to find some that still hold a decent charge.
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PDXMark Page Icon Posted 2009-11-27 1:35 PM
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I've found 12 batteries so far that still hold enough of a charge to be useful, plus two surplus battery chargers that were going to be junked or given away that still work just fine. So now I can recharge at work and home. Looks like I'll be using batteries for now, until I can figure out what the issue is with the ac adapter.

The nimh batteries work well - I get a few hours of use between charges. I'd probably get more time with new batts.
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