Roomba 780 right wheel resistance with battery

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Re: Roomba 780 right wheel resistance with battery

Postby pawel2m » February 15th, 2014, 4:10 am

Thx, Gordon I will switch the roomba into the Test Mode and check it the way you suggested. This Roomba was damaged by customer who "did not have the time to think" and washed out the doggies poop with running water direct to CHM (without taking the battery out).

PS. I have uploaded hires photo of 7xx mainboard for future reference.

two.jpg


one.jpg
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Re: Roomba 780 right wheel resistance with battery

Postby Gordon » February 15th, 2014, 2:30 pm

Thanks for the pix. After scanning them I see no evidence of any "Quad NOR-gate" ICs, hence, my notion that iRobot's EE designer of the 7XX motor-control circuits decided to forwarded that logic service onto the 7XX-main_PCA is incorrect!

Thus, with that in mind, I can only guess that all four reversible motors are now directly controlled by three or four MCU ports, per motor.

An older R2-Roomba wheel schematic may now be more relevant to 7XX than my suggested R3 version. If interested, search for schematic5, and while viewing that diagram mentally substitute dual-MOSFETs for the illustrated BJT power xstrs, and modify the number of buffer xstrs (looks like four are used as 7XX FETs' driver/buffers, vs only three in the R2-circuits).

While measuring signals on your 7XXX CHM-motor's circuit, you might check for activity at base pads of Q71, Q85, Q41, Q13 after engaging that motor's BiT#. Level shifts ought to be seen--I'm guessing.

If those level shifts are seen, then make sure the collector voltages of those xstrs also follow. Verify that corresponding shifts occur at all gates of: Q66 & Q67.

If all of that works OK, then shift attention to the 7XX's right-wheel bridge and repeat measurements on its buffers and bridge gates.

Also: Are you certain that the PCA is totally dry?
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Re: Roomba 780 right wheel resistance with battery

Postby pawel2m » February 15th, 2014, 5:27 pm

Hello, yes it's completely dry now. Cleaned with IPA and dried in 60 deg (Celsius).
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Re: Roomba 780 right wheel resistance with battery

Postby fishpepper » March 3rd, 2016, 5:08 pm

Hi!

First of all thanks for sharing that information. It helped me to bring my 780 back to life :)
I want to give some information back, maybe it is useful to others.
My 780 was water damaged, not very much but to some degree. I had to replace the connectors for the CHM and one Wheel (got them from a dead 5xx circuitboard). My symptoms were: resistance when rotating the left wheel, wheel not working at all.

The first thing i would like to share is that indeed the C3035LD and STS8C5H30L are interchangeable. I replaced two dead C3035LD with the STS8C5H30L ones and they work fine.
I had to replace a broken 0.1R resistor that brings GND to the left H Bridge. Two of the 7.5V Zener diodes (SOT23, marked as Z6, BZX84C7V5) were broken (instead of measuring 0.5xxV voltage drop with my multimeter they got ~1.9V).

Two small Mosfets labeled 702 were broken as well (SOT23, 2N7002).

Things without warranty / were i am not 100% sure:
- the sot23 transistors labeled H2 could be BCW70 transistors
- the sot23 transistors labeled 2T could be mmbt4403 transistors
But i am not sure with those, the markings have three digits on mine, i guess those might be the plant or some datecode. But please be careful, this might be the wrong types. I did not verify this further as i did not have to replace those at all...

When testing this stuff make sure to use a limited current power supply. And as stated above, make sure the mosfet control signals (gate) are valid before soldering in new mosfets and the 0.1R shunt ;)

My measurements on the good motor showed:
Forward: G0 = 0V, G1 = PWM (switching from 7-15V), G2 = 5V, G3 = 15V
Reverse: G0 = 5V, G1 = 15V, G2 = 0V, G3 = PWM (switching from 7-15V)
(G0, G1 = the left mosfet, G2, G3 the right one, counting from left to right when the front of the roomba is facing you).

Just for the records, my broken one had: G0 = 5V, G1=PWM, G2=5V, G3 = PWM -> shorting VCC and GND :-\

Maybe it saves someone some time ;)

Simon
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Re: Roomba 780 right wheel resistance with battery

Postby whitecube » July 21st, 2016, 2:35 am

In advance, sorry for my bad english ;)

i bought a faulty roomba 780, the right wheel wasnt moving.

over Q60 the plastic changed to white from the heat. i unsolderd Q60 and as fispeppers mosfet it is shorted.
then i replaced Q59,Q60 and the R96 (0,1ohm), now its moving forward, but the right wheel isnt turning backward.

can anyone help me to find the error?
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » July 21st, 2016, 6:01 am

Remote troubleshooting.
Check continuity between transistors and wheel connector, Vbat and Gnd.
You may need to add a jumper between the transistors and one of the above, bad board trace or solder joint.
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Re: Roomba 780 right wheel resistance with battery

Postby whitecube » July 21st, 2016, 8:12 am

didnt found a schematic for 7xx series, does someone have one?

or some testpoints that i can check and verfiy voltage?

edit: does anyone know where i can buy the Z6 diodes?
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » July 21st, 2016, 2:58 pm

No schematic for 700s as of yet.
500 schematic, the transistors from 500 have been replaced with the duo n/p channel FETs on the 700s.
http://www.robotreviews.com/chat/viewtopic.php?f=1&t=16618
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Re: Roomba 780 right wheel resistance with battery

Postby TnT » September 12th, 2016, 3:46 pm

Has anyone identified the specific issue (electrical connection), for the 5 Right Error, and given the additional details:
Battery removed, Right wheel has twice the resistance as the Left;
Right wheel assembly removed, Wheel now same resistance as left (while left wheel assembly is still installed);

Plug right wheel assembly back in (battery still removed), and resistance doubles again. Remove and resistance is same as left.

This would seem to be some type of resistor, or other electrical connection (sorry, not in any way an electrician... or savvy with electrical connectors)... :(

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Re: Roomba 780 right wheel resistance with battery

Postby vic7767 » September 12th, 2016, 6:36 pm

Your drive motor becomes a voltage generator when turned by hand. The H-Bridge components for that wheel have a defective component on the main board.
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » September 12th, 2016, 7:06 pm

Q59 & Q60 N Channel Fets Source pin1 = 0.15ohm to GND.
Q59 & Q60 P Channel Fets Source pin3 = 0ohm to VBAT.
Q59 N Channel Drain pin7/8 & Q59 P Channel Drain pin5/6 0ohm to Wheel Connector pin 1, my notes wheel Reverse
Q60 P Channel Drain pin5/6 & Q60 N Channel Drain pin7/8 0ohm to Wheel Connector pin 2. ...Forward +V 2 to 1
Without running the bits and the board exposed, turn the bot on standby mode. Green LED Lit not running.
Read Voltage from pin 2 of wheel connector to GND. Should be 0V, if much higher problem Q60.
Read Voltage from pin 1 of wheel connector to VBAT. Should be 0V, if much lower, negative, problem Q59.
Last edited by a1robotrepair on September 14th, 2016, 12:52 pm, edited 1 time in total.
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » September 12th, 2016, 9:56 pm

I have been trying to get my head around wheel resistance with battery removed.
After long thought, the only explanation is one of the duo Fets has internally failed allowing a short between the N & P channels. Now I need a board to trace a drive circuit and verify.
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Re: Roomba 780 right wheel resistance with battery

Postby TnT » September 13th, 2016, 10:35 am

vic7767 wrote:Your drive motor becomes a voltage generator when turned by hand. The H-Bridge components for that wheel have a defective component on the main board.


Is there an easy way to isolate the mainboard problem? I would assume fixing the issue would be much less expensive than replacing the mainboard (that is, if the mainboard can be purchased and replaced).
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Re: Roomba 780 right wheel resistance with battery

Postby vic7767 » September 13th, 2016, 2:35 pm

Read the reply prior to mine by a1robotrepair for the suspected device that needs replacing. 600 through 800 model Roomba main boards (PCAs) are more expensive since they are newer models offered at higher prices.
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Re: Roomba 780 right wheel resistance with battery

Postby whitecube » September 14th, 2016, 2:09 am

Look at eBay, there is a Guy from Japan with new boards. Take the cheapest. The rf Module is on the smaller Board so you only habe to replace the big one
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » September 14th, 2016, 8:22 am

Checked my notes. Forgot about D63 & D64 reverse biased Schootky diodes used to collapse the motors EMF while stopping or slowing down.
They are from the motor connection contacts pins 1 and 2 to System Return, bypassing the motor current sense resistor.
They will have a very low forward break over voltage, below 0.2V current dependent.
If one of the FETs has failed closed or driver circuit is exciting the gate, spinning the wheel will try to push current against itself.
Last edited by a1robotrepair on September 15th, 2016, 7:47 am, edited 1 time in total.
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » September 14th, 2016, 9:43 pm

This drawing is from NOTES I made from the 1 700 right wheel I repaired, replaced Q60 and D63 Schottky diode.
Most importantly, the wheel module caused the PCA malfunction, it was also replaced.
Resistor are SMD code values, not OHM values.
fishpepper wrote'
I had to replace a broken 0.1R resistor that brings GND to the left H Bridge. Two of the 7.5V Zener diodes (SOT23, marked as Z6, BZX84C7V5) were broken (instead of measuring 0.5xxV voltage drop with my multimeter they got ~1.9V).
I have these as 26 as opposed to Z6 marking, D214 & D215. I think fishpepper is correct as my old eyes aren't what they used to be. Note this during your repair. BZX84C7V5-V Vishay.
Corrected D214 & D215 and Duo FET numbering. Edit 2, added 2nd page of notes. Third and fourth pages coming soon.
700-RIGHT-WHEEL-2 (3).png
Last edited by a1robotrepair on November 15th, 2016, 4:32 pm, edited 9 times in total.
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Re: Roomba 780 right wheel resistance with battery

Postby TnT » September 15th, 2016, 9:10 am

a1robotrepair,

You've done a great job explaining and documenting this, very much appreciated!!

Tom
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Re: Roomba 780 right wheel resistance with battery

Postby TechGuy » September 16th, 2016, 5:54 pm

It is the time for me to take the water damaged 880 with the error 5 left wheel problem out to do some measurement on the H-bridge components. Testing it with known good left wheel did not fixed the problem.
Charging battery directly: 400 Series, 500 Series,.H-Bridge Repair How to Desolder
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Re: Roomba 780 right wheel resistance with battery

Postby a1robotrepair » September 16th, 2016, 7:52 pm

Let me know and I'll open the drawing document so hopefully you can verify and add to it.
My measurements on the good motor showed:
Forward: G0 = 0V, G1 = PWM (switching from 7-15V), G2 = 5V, G3 = 15V
Reverse: G0 = 5V, G1 = 15V, G2 = 0V, G3 = PWM (switching from 7-15V)
(G0, G1 = the left mosfet, G2, G3 the right one, counting from left to right when the front of the roomba is facing you).

I would verify these readings on the the left wheel, looking at my drawing I would expect Q60 P to Q59 N forward and Q59 P to Q60 N reverse. Not Q60 P to Q59 P .......
The motor connector pin nos. may be 5 & 6 as opposed to 2 & 1. The difference between electronic/electrical codes.
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