Replacement adapter for MP 790

I've been looking for a non-OEM replacement AC adapter for my MP 790, and came across this thread from a couple years ago: http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=8451&posts=3

I know I need 9v and minimum 1000 mA. I've been looking on eBay and came across several possibilities, but I'd like to be sure I'm getting the right thing. Would something like this work: http://cgi.ebay.com/9-Volt-1000mA-AC-to-AC-Wall-Wart-Adaptor-US-Robotics-9V_W0QQitemZ300314647798QQcmdZViewItemQQptZBI_Circuit_Breakers_Transformers?hash=item45ec25dcf6

The only difference I can see is the input is 12.9 W, and the original MP 790 adapter is 13 W.

Edited by PDXMark 2009-11-01 11:59 PM

Well, another issue is whether or not the tip size is correct since any standardization seems to beyond my "junkpile" experience. Obviously a non-issue if you have a non-function OEM transformer on-hand (just make sure the tip polarity is correct).

The power listed is the input (AC) power draw. There's some amount of (normal) inefficiency since the DC output power is 9W (from P = V*I = 9V * 1A). 1A (or 1000 mA) isn't some magic number; any less translates into a longer charging time. The 1A value allows the unit to operate while charging at some acceptable rate. Somewhere else on this site (good luck finding it!) its been reported that they were able to run off of as low as 400 mA (IIRC, but who knows...), but charging only occured when the unit was off.

For that price ($13 after S&H), you might be better off visiting Radio Shack on a sale day (they sell a unit with interchangeable plugs; the first is free) or looking for R/S transformers at the thrift stores (and then picking up the right modular plug, if needed).

Alancomputeech has the AA adapter pack for $9 (plus $8 shipping...) as well as the desktop battery charging cradle (which I ended up getting since I started worrying about the charging circuit dying ... which it did 2 months later (on an OEM charger)).

What about a universal adapter, like this one: http://www.newegg.com/Product/Product.aspx?Item=N82E16882143076&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Mobile+Electronics+Accessories-_-jWIN-_-82143076

PDXMark...that universal adapter looks just like what the doctor ordered....good find.

One thing I just noticed is that it's rated at 18W, and the OEM MP adapter is only 13W. Does that matter? (you can tell how much I know about this.....)

It's more power than you need, but the device will limit itself. It's really not an issue; if it suddenly decides that it wants to draw 18W, you have other problems that the OEM adapter wouldn't help anyway... The power ratings are basically maximums. When the unit is fully charged and off, the power consumption is very low. When the unit is on and running fully, it should be current limited so that it'll only draw 10-11 W maximum. Said another way, as long as the unit really only providing a 9V potential, it'll never want more than 1A.

Thanks, everyone. I'm thinking I'll go the universal route. OEM adapters are hard to come by these days, unless you buy the device with it.

Wise decision. That's what I'm doing with my 790 - I use my trusty Tekkeon universal power supply when it's time to charge it up.

The 18W shows the maximum when set in the 12V position...when set in the 9V position the power will be less....

So the adapter arrived tonight.....I set it to 9V, selected the only one of the 6 included tips that fits in the 790.....and it's not working. :-( I know the battery is good, because the unit powers on OK with battery power. But it isn't drawing any juice when plugged in - doesn't light up and the power screen doesn't indicate that it's charging.

Could it be that the tip size isn't quite right (even though it seems to fit)? I don't have my OEM adapter here (I gave it to someone to try to repair), so I can't compare the tip sizes. Or could it be an issue with the jack? How would I check for that?

It could be that the tip is not quite right. The jack in the 790 (and 900) seems to be a somewhat less common size - and it seems to get loose rather easily. The tip I use with my Tekkeon is a bit oversized and thus tight in the jack, but this prevents the connection from wiggling loose.

Also look down the barrel and the diameter of the hole and see if it appromates the size of the center pin. I've had tips that fit in the device, but the center hole was so large it didn't make contact with the pin...requiring me to insert some aluminum foil to make up the space. I had another that the insulator on the tip was too long and had to run the adapter tip on the grinder and take it down a mm or two...

How did you fit the foil in there?.....the space is pretty tight. The tip seems like it's going in all the way, but some is left outside when it's fully inserted. I'm a little hesitant to grind off the end because then I can't return the adapter.

If it is tight...then it is probably fine....and if there is some and it's not going all the way in...well it might just be a longer plug which is okay too. Look at the insulator at the tip and if it is thin then no sense in grinding at all...but if it is big...like 3/16 of an inch, then perhaps it is preventing contact with the contacts in the Mobilepro.

If you have a universal adapter, one that takes those tips with the two pins...which is the common style/factor, then go to Radio Shack and compare the tips and sizes as they sell the adapter tips separately there....

You didn't say, but you did check the tip polarity, right?

Also, if you have a multimeter (or another device that fits), check that the PS itself it working.

Otherwise, I'm all out of easy troubleshooting...