Sencor SVC7020BK robot vacuum cleaner problem

[Awesomerp]

Hello I have been trying to identify and fix a problem with a robot vacuum cleaner, which when switched on cleans for like 3-4 seconds and stops, all the driving, sweeping and vaccum motors stop.
On the pcb from a battery connector up to a main microcontroller everything seems to be fine (vcc pin input is 5v constant when a switch is switched on).
And the switch itself is fine looking at the quality of my soldering
Red LED keeps blinking during those 3-4 working seconds, and when the robot stops LED just remains lit.
The green one for some reason does not even blind/shine i think the volage does not even reach it or not enough to say at least.

What I figured so far:
Battery charges( but as previously said green LED should blink when it charges but doesn't and i tested led is good, when i put my Multimeter probes across it, I can see clearly that it blinks but when i remove it ,it stops, so it means not enough voltage is supplied from the main controller?)
5V linear regulator is working
All the motor drivers look in shape, but stop working after 3-4s period
Step down regulator does bring down voltage to 8.3V which is good.
The D16 diode when checked with a multimeter on diode mode shows 3.2V in reverse biased but when i remove it and test it, its 0 don't really know why.


If someone has any ideas or tips of what could be the case of this problem, would really appreciate your insights
It is interesting what makes him switch off and I assume that the main microcontroller does the switching right?
I am pretty new and trying to understand the whole working principle so shared knowledge would be awesome.
I am also attaching images of pcb layout and schematics.
Only the photos are mine so credits to the person who made the reverse engineering of pcb and schematic.

[stj]

you should find a manual to see what the leds mean.

looking at the schematic, 2 things i noticed.
1: the "charge circuit" is bullshit, charging a 14v battery from 19v with a 6ohm resistor is sooo cheap!
2: the psu for the motors has a sense circuit - maybe it's detecting an overload?
did you check the 8.3v??

[Awesomerp]

Yeah the vacuum cleaner it self was pretty cheap, I guess they could not be bothered to make a better charging circuit
1.And about the power monitoring circuit yeah 8.3v across the R7-R6 resistors is present, if you were talking about this circuit.
2.They claim that red lit led means: the battery is flat or the cleaner is lifted of the floor. The battery seems charged to me. 14.4V on the meter. The green one seems not to get a proper voltage.
3.Maybe you know why the D16 diodes "Reverse" voltage is displayed 3.2V while in circuit. (while in diode checker mode on multimeter)?

[stj]

change the LM393, it's the only thing that could show a low battery if r6,7,8 & 9 are o.k.

d16 if you look, has a bypass - r8,9,10,5 and j28
all in series allows the diode to be bypassed via ground.

[Awesomerp]

R6- Measure- 6.8kΩ, Schematic - 18kΩ
R7- 3.9kΩ, Schematic - 4.7kΩ
R8- Measure 50kΩ, Schematic - 68kΩ
R9- Measure 16.7kΩ other polarity 30-45kΩ(increases over time), Schematic 56kΩ.
I can't tell if i can't get a good reading of how small they are or their resistance is actually lower than has to be. (strange that all of them act up)
I tried with 2 multimeters and the results were similar.
Voltage across (R6,R7) to ground is 8.3V and across (R8,R9) to ground is 13.8V.
I think i will try ordering and replacing resistors first, if the problem will still occur ill replace the comparator.
Thank you for your help I will update when the parts arrive and how it goes.

[petehall347]

resistors might be fine if as i suspect you measured in circuit ?
i would look more towards the motor itself . it could be running at the wrong speed .. maybe jammed slightly from hair balls or something .

[stj]

lift one end of each resistor before testing, your metering the internals of the lm393 at the moment!

[Awesomerp]

Yeah i did it in circuit

[Awesomerp]

Sweeper motors draw 7.4V
Drive motors draw 8.2V
Vacuum motor draw 12.2V
Tested while it operates those 3-4 seconds until it stops.

[petehall347]

this is where the figures lose me . need to know what is expected .

[Awesomerp]

About the motors:
1. Drive motors are 8V 8000rpm
2. Sweeper motors are smaller rated at 8V 6000rpm
3.Vacuum motor is rated 8V 6000 rpm but bigger than sweeper ones.

1.Drive motors seem fine since they do get 8.3 while running
2.Sweeper motors get about 7.4 while running but when the robot stops it goes up to 8V.
3.Vacuum motor while running draws about 12.5V, when the robot stops voltage rises to 13.5.

I have shown the the voltages in the circuit diagram (in vacuum and sweeper motor parts).
1. Red values indicate voltage after robot stops.
2. Blue values when it is running those 3-4 seconds.

I suppose that initially the diode drops 0.6V from 14.4 which we can say is 13.8V approximately 13.5.
The question would be is the Voltage suppose to drop to from 13.5 to 12.5 while its running?

Also looking at the JP1 of vacuum motor connector on:
Pin1 voltage is present but I think Q22 transistors is being turned off (not getting proper voltage at base I assume) after 3-4 seconds that's why pin 2 does not get a voltage and the vacuum motor stops operating? ("well all of the motors stop operating").

[stj]

if you turn the motors by hand, is there any friction or are they spinning o.k.?

[Awesomerp]

Yeah they are okay, spinning freely.
There are ceramic caps on each of the motors is there any chance they could cause the problem?
Do not have an ESR meter to test them.

[stj]

ceramics either work or go shorted - and then they would burn.

[Awesomerp]

I see, thank you for the info, what about coils or electrolytic caps? Can they impact this behaviour? Now talking about the main circuit.

[stj]

get back to that lm393 - maybe check it's output signal under load

[Awesomerp]

Black probe on the ground and went through all the pins with the red one here's what i got. (picture)
Voltage was constant with load and when it stopped.
Only 8 pin changed a little:
Load - 13,05V
Stopped - 12,85V

[stj]

that makes no sense, how can the battery voltage rise under load?

[Awesomerp]

My bad:
Stopped - 13,05V
Load - 12,85V

[Awesomerp]

Well something with the charging circuit seems to be wrong too.
Left a battery to charge for an hour and now it is 16.3V instead of 14.4.
R72 got real hot.
The values of the resistors are good.
I suspect Q11 and Q12 surface mount transistors to be the culprits, will test them tomorrow.
What do you think?