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Step 9: U2/U4 Fix

What causes this? While the cause is not completely determined, one reason may be charging your completely discharged battery.

In most cases, both the U2 AND the U4 mosfet need to be replaced. This part will not only fix it, but make your Roomba less susceptible to this type of damage in the future. http://www.mouser.com/ProductDetail/STMicroelectronics/STN3PF06/?qs=du%252bo5tJIeNKF3dCiL6LdRg%3D%3D The whole procedure should only cost 3 dollars!

To remove and install this part, a SMD Rework Station will be used. (An Aoyue) Just use your hot air soldering iron to desolder the part, dispose of the part so you don't get it mixed up, then put solder paste on the pads and install your Mouser part. The Parts you need to be replaced are on different sides of the board,  and labeled U2 and U4 hence the name. First picture is of U2, second is U4. Schematic made by RobotReviews Member Gordon: http://mysite.verizon.net/gsplews/misc-pix/charging_n_control_schema.GIF

To reassemble, just follow the steps backwards. 
<p>Just purchased in Ali Express as well! will let you know once it was fixed :)</p>
<p>Hi, does the parts from Aliexpress fix the charging problem? Thanks</p><p>Nguyen</p>
<p>Didnt work for me unfortunately, but feel free to try for yourself</p>
<p>Thanks, I'll try anyway. Still waiting for the mosfets from aliexpress</p>
<p>Where exactly are the both mosfets located</p>
My roomba would not charge, it would slowly blink red while charging and then green after many hours. I unplug and try to turn on and get nothing. Plug it back it and get the same slow red pulse as if i never chargwd it. Anyway, i did exactly as this post said and i also took the advice of jasontaylor71 and upgraded both mosfets. You dont have to completly remove the board. Just enough to get at the 2 mosfets. Reassembled and it works perfectly. I almost threw my roomba in the trash but tried this fix for $7(ordered 3 just in case). Fun little project. THANKS!
<p>Thanks to JasonTaylor71 the parts from </p><p><a href="http://www.aliexpress.com/snapshot/6813300145.html?orderId=68433872188537" rel="nofollow">http://www.aliexpress.com/snapshot/6813300145.html...</a></p><p>Worked great. It was a small pain to get the board out; however very worth it. </p><p>Carlos Leon</p>
<p>Regarding step #9 only (the charger circuit repair), I'd recommend upgrading both of the failed mosfets. ss_star9 sells a set of Diodes Incorporated ZXMP7A17GTA P-ch 70V 3.7A SOT-223 for $3.32 including shipping. Current webpage is <a href="http://www.ebay.com/itm/301534034343" rel="nofollow"> http://www.ebay.com/itm/301534034343 </a> . (Mouser charges a lot for shipping so their cost is not only $3 for two STN3PF06.) The old parts could handle only 2.5A. <br>I hope this helps anyone doing this repair.<br>Cheers,<br>Jason Arthur Taylor<br>jasontaylor.us</p>
What's going on between step 8 and step 9? After step 8 there's still about 30 connections of wires, springs, mounts, etc to the main board.
I have a roomba 400 that the beater bar/brush assembly runs constantly. Pressing the CLEAN buttonturns the unit on and it goes through the cleaning motions but depressing it again to turn the unit off turns off everything except the beater bar/brush assembly. Suspect a shorted driver chip or transistor. Are there schematics available for these older model Roombas and if so where? Thank you.
great video for others having problems with charging circuit <br>i use Gordons schematic alot for repairs and upgrades <br>i have alot of roomba's for different robot designs i am testing <br>like TURTLEBOT using ROS software,and SERVERBOT design and yours <br>i like it better then my IROBOT CREATE,its low cost,plenty of room once you remove the vacuum parts and can handle up to 35 lb carring load

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