780 getting stuck 'pushing down' walls

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780 getting stuck 'pushing down' walls

Postby Wazzu8 » February 11th, 2018, 6:42 pm

I have a Roomba 780 and the right wheel tread got worn out due to roomba try to 'plow' through a wall repeatly and not redirect itself another direction. I replaced the wheel tread with some toy RC rubber tread, replaced the IR sensors for the walls and the bumper sensors, and have done a full cleaning of the robot. It does a bit better but is still doesn't act like it use to... any suggestions? Symptoms is that it keeps trying to go forward into a wall and now eventually turns another direction for the most part. When it hits the left bumper it works pretty good (changes directions) but the right bumper is really bad. I haven't seen any error codes and cannot get it into diagnostic mode either.. (following the press the clean button, dock and spot etc..).

Update: Added video for better understanding.. https://www.youtube.com/watch?v=6nDo5bHN4Ek

Thanks!
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Re: 780 getting stuck 'pushing down' walls

Postby vic7767 » February 11th, 2018, 8:49 pm

Wazzu8 wrote:cannot get it into diagnostic mode either.. (following the press the clean button, dock and spot etc..).
Use two fingers of one hand to press down both the clean button (keep it pressed down) and also press down the dock button and keep it pressed down. While those two buttons are pressed down with your other hand press the dock button down and release it 6 times in a row, then release all buttons. The Roomba will play a tune and you will be in the manual bits mode.
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Re: 780 getting stuck 'pushing down' walls

Postby Wazzu8 » February 11th, 2018, 9:52 pm

"with your other hand press the dock button down and release it 6 times in a row" you mean spot? either way, I've tried it and no dice unfortunately...
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Re: 780 getting stuck 'pushing down' walls

Postby vic7767 » February 11th, 2018, 11:29 pm

Wazzu8 wrote:" you mean spot?
Yes, lol. When pressing down the Clean button, it should not light up during this procedure until after the 6 pushes of the spot button and releasing of all buttons.

BTW, your video does indicate that the right bumper sensor is not working.
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Re: 780 getting stuck 'pushing down' walls

Postby TechGuy » February 12th, 2018, 12:02 am

My guess is that one or both wheels does not rotate in reverse direction. When it bumps into wall, it does not move backward and keep driving forward-stop-forward-stop... sequence.

Use a masking tape to tape the bumper to Roomba body to simulate bump sensor failure. If it doesn't move backward in circle, wheel does not rotate backward.
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Re: 780 getting stuck 'pushing down' walls

Postby Wazzu8 » February 12th, 2018, 12:37 am

@ TechGuy - I think you are on to something. It does look like the left wheel cannot go in reverse which would cause this symptom! The right wheel for sure can go in reverse.
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Re: 780 getting stuck 'pushing down' walls

Postby TechGuy » February 12th, 2018, 1:08 pm

Test the left wheel motor with a 9v battery. If it rotate both direction by changing the voltage polarity. If it works both directions, the left wheel H-bridge is the problem. I have not successfully repaired a 700/800 serires H-bridge yet. Wait for a1robotrepair to give you repair tips. You may search this forum for his notes. Good luck.
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Re: 780 getting stuck 'pushing down' walls

Postby Wazzu8 » February 17th, 2018, 10:29 pm

Thanks TechGuy... I unfortunately didn't have cabling / banana clips etc to test the wheel with a 9v so i bought a Left Wheel... Of course, it still has the same issue... Probably why the 700 series was discontinued... I'll be looking for the H-bridge fix...

Thanks
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Re: 780 getting stuck 'pushing down' walls

Postby TechGuy » February 18th, 2018, 3:06 pm

Wazzu8 wrote:Thanks TechGuy... I unfortunately didn't have cabling / banana clips etc to test the wheel with a 9v so i bought a Left Wheel... Of course, it still has the same issue... Probably why the 700 series was discontinued... I'll be looking for the H-bridge fix...

Thanks

If you cannot do a simple test on a motor with a battery, you may not be equipped to do H-bridge repair on your 780 motherboard which you need a hot air rework station to replace the surface mounted driver chip. It will be easier for you to replace the 780 motherboard.
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Re: 780 getting stuck 'pushing down' walls

Postby Wazzu8 » February 21st, 2018, 11:51 pm

Probably will get a new board... or a new robot.. but was going to run this pic by you guys to see if R168 would be the issue and if it would be a quick easy fix for a right wheel not going in reverse?
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IMG4235 copy.jpg
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Re: 780 getting stuck 'pushing down' walls

Postby vic7767 » February 22nd, 2018, 12:29 am

Q51 is not looking too well either as well as R168. Actually several soldered connections on that board are suspect. It may be easier to replace that board.
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Re: 780 getting stuck 'pushing down' walls

Postby Wazzu8 » March 8th, 2018, 10:37 pm

Replaced the board (about $80 on eBay) and everything is working. Thanks!
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