Help with Roomba 581 repair - Burned out FB14 [Solved]

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Help with Roomba 581 repair - Burned out FB14 [Solved]

Postby Wickeido » July 8th, 2013, 4:35 pm

Hello,

searching for information about Roomba repair I've landed on this website, and it seems to be a nice source of information :D

I've bought a faulty Roomba on Ebay, and the seller described it as "Faulty battery". When it came home, it won't charge, but also it doesn't do anything more, no lights, nothing.

I've measured the battery pins and there is no power, so the problem seems to be in the motherboard. I've taken out the motherboard and yes, there is a problem, a blown up burned area.

You can see the burned area in the attached picture, and the arrow points out the burned component.

Could someone tell me what component it was? And also where it was connected (the area around the component is also burned, so I can't see where it was connected).

That way I may be able to fix it and get it working again.

Thank you very much!
Attachments
281.jpg
Last edited by Wickeido on July 14th, 2013, 1:57 pm, edited 1 time in total.
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Re: Help with Roomba 581 repair

Postby Gordon » July 9th, 2013, 12:11 pm

That device is a P-channel MOSFET that operates as the switching transistor in Roomba's buck-convertor to down convert battery voltage to a regulated five-volts source that is used many places on that main board. See its (Q7 board marker) P/N in the schematic diagram shown in this post: viewtopic.php?p=83059#p83059

IMHO, if the PCB's surface is scorched as badly as you claim I think there might be more wrong with that main_PCA than just the failed Q7 MOSFET. The +5VREG supply bus is not heavily loaded. I does not drive any of Roomba's motors. You can try replacing Q7, but don't be surprised if that fails to make Roomba function properly.
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Re: Help with Roomba 581 repair

Postby Wickeido » July 9th, 2013, 1:32 pm

Hello Gordon,

thank you very much for your answer. If I understand well, it's not the MOSFet that is blown up, it's a Ferrite bead marked with FB11 (I've been looking to pictures of another boards and it looks like it).

I've managed to take a picture of the area. My idea is to wire directly the components, as there are no pads left. I would try to measure where the conections go, but as the pads are burned out, I can't figure where they've gone.

I don't see the FB11 in the scheme in the link you provided :(

Thank you very much for any asistance!
Attachments
Tue Jul 09 18-47-21.jpg
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Re: Help with Roomba 581 repair

Postby Gordon » July 9th, 2013, 4:37 pm

Wickeido wrote:...thank you very much for your answer.
Welcome!
... it's not the MOSFet that is blown up, it's a Ferrite bead marked with...
FB14 (not "FB11").
... My idea is to wire directly the components, as there are no pads left. I would try to measure where the conections go, but as the pads are burned out, I can't figure where they've gone. ...I don't see the FB11 in the scheme in the link you provided ...
Now that you have the correct marker you can see FB14 in the schematic diagram, upper right, grouped with components L1, C287, and D55.

I don't have any procurement data for a FB14 replacement, but, for starters I measured its chip size at ~= 3.3 mm LG X 1.7 mm W X 1 mm THK.

You might also start worrying about D55's health, since it is in series with FB14!

D55 is a bottom mounted, axial leaded discrete power diode located next door to the toroidal inductor L1. In the schematic I show D55 to be a Schottky type diode. I believe I did so because switchers usually require Schottky characteristics, however, I am certain that I did not dismount D55 so I could read its package marking! IOW, I don't know its P/N.

Good luck with the repair.
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Re: Help with Roomba 581 repair

Postby Wickeido » July 14th, 2013, 1:56 pm

Good news!

I managed to repair the poor thing! After reading the scheme that Gordon showed me, I rewired some of the paths, and cut other ones. And, voila, it worked!

Below you can see what I have did, in case someone has a similar problem. Maybe what I did is barbaric or ilogical for someone who understands electronics (I've only basic knowdledge) but it works!

Thank you again Gordon for the information!

1. First thing I did was to measure continuity between the pin that comes from the D55 Diode to the lost Ferrite Bead and the ground pad near. There was in fact continuity, and there should not be, because the Ferrite bead is not there to act as bridge between ground and the D55.

2. I measured continuity between C287 and the D55 pin. Looking at the scheme, there should not be continuity, the missing FB14 is breaking the line.

3. I figured out that there was something wrong with the pad where the D55 pin goes. My idea was to isolate the Pad, and wire the componentes separately. Y cut the path at the sides of the pad, on the upper side of the board and on the lower side also. Also cut the D55 from the pad. I rewired the D55 with 3 wires. 2 to continue the original path, but outside the faulty pad area. The remaining one was soldered to a ... don't kown if it really is a Ferrite bead. I extracted the thing from a faulty graphic card, it was near the electric conection and had a low impedance, so... let's give it a try.

4. The upper side of the faulty Pad was serving as ground for a small connector, and it wasn't connected to the other pads around the board, so I wired it directly.

I've attached pictures of what I've did! Sorry if the explanation is not very good, my technical english is not the best. And a video of the poor Roomba living again!

Attachments
Image_3.jpg
Everything isolated with tape.
Image_4.jpg
Isolated Pad on the upper side, faulty ground Pad wired to another Pad. 3 wires from D55 pin to their respective paths, and 1 to the Ferrite Bead
Image_2.jpg
The possible Ferrite Bead and direct groud connection from the faulty pad of the upper side.
Image_1.jpg
Here te isolated D55 pad, and C287 wired directly to ground.
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Re: Help with Roomba 581 repair

Postby Gordon » July 14th, 2013, 4:52 pm

Wickeido wrote:Good news!

I managed to repair the poor thing! ...
Nice work Wickiedo, you pulled that robot back from its grave! I am surprised, because the severe charring of the PCB might very well have resistively connected surface tracks of copper to interior tracks, thus adding mystery to a repair attempt.

So, Roomba may be able to perform floor cleaning, but your video reveals two things that are not normal. 1) When a docked Roomba is told to start a mission, it should reverse travel away from its dock apron far enough so when it rotates to drive away there is no chance of dragging its Home Base with it. Yours began turning while still over the dock!

2) Roomba seemed to be driving faster than it should in the clutter of furnishings and exhibited some hard bumping. Some of those could have resulted from furniture structures that are too narrow to adequately reflect enough of the IR beams' (fanning out in front of Roomba) energy back to the robot. You might try watching your fast driving Roomba as it approaches normal (+/- 45 degrees) to a wall to see if it slows before striking the wall. That would be its normal response.

Regards;
---Gordon
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Re: Help with Roomba 581 repair - Burned out FB14 [Solved]

Postby Wickeido » July 14th, 2013, 5:47 pm

Gordon wrote:1) When a docked Roomba is told to start a mission, it should reverse travel away from its dock apron far enough so when it rotates to drive away there is no chance of dragging its Home Base with it. Yours began turning while still over the dock!


Yes, it dit turn on the Home Base! It's strange. Since the video I've taken it apart again, because for testing it I din't put all the screws on place, so it will be easier to open in case I needed to test something.

Since it was overall working, this time I assambled it completely. Now it seems to follow the correct routine, it moves away from the base first, and then it starts cleaning.

I'll keep an eye on it anyway...

Gordon wrote:2) Roomba seemed to be driving faster than it should in the clutter of furnishings and exhibited some hard bumping. Some of those could have resulted from furniture structures that are too narrow to adequately reflect enough of the IR beams' (fanning out in front of Roomba) energy back to the robot. You might try watching your fast driving Roomba as it approaches normal (+/- 45 degrees) to a wall to see if it slows before striking the wall. That would be its normal response.


Sometimes it slow down when getting near an object, other times it bumps it. It happens with my sofa that is black and some puffs that are dark also. The white furniture it's a gamble, sometimes it hits it other slows down. Could be the sensor? It's almost 2 years old, maybe the sensor is not in good shape...

Gordon wrote:Nice work Wickiedo, you pulled that robot back from its grave! I am surprised, because the severe charring of the PCB might very well have resistively connected surface tracks of copper to interior tracks, thus adding mystery to a repair attempt.


Thats why I isolated that burned Pad, there was something wrong with it. Truth is that I've been lucky with this repair, when I saw the black burned area, I don't expected to have a working Roomba in a couple of days. And even with some glitches like not slowing down on some furniture, it cleans allright and I got it for a good price, with 3 virtual walls and a remote controller. So I'm pretty happy!
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Re: Help with Roomba 581 repair - Burned out FB14 [Solved]

Postby Harry007x1 » August 16th, 2016, 8:02 pm

The reason it drags the base is due to a failed IR in the top of the dock, the halo IR. I have seen many fail and exhibit that exact same behavior. It will also crash into the dock during cleaning.
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