Mower 5VP, 3,3VP voltage troubleshotting

[slatkowski]

Hi All,

Yesterday my mower stopped responding. I can't connect it via bluetooth. When connecting with USB cable and testing I2C Arduino DUE could not find any device. 5VP and 3,3VP LED on ver. 1.3 PCB are off. All others are on. I've read through the docs and schematics for the PCB 1.3 and I couldn't find the cause of this issiue. Could someone guide my how to diagnose this, please?

Thanks in advance.

 

[slatkowski]

Hi,

I've measured the voltage and current on the first 9V->5V LM2940CS-5.0 voltage regulator. The voltage drops to ~1V. Current is very high at the beginning up to 2A after the board starts and drops to ~500mA after a while, but the voltage is still very low. The 9V->5V regulator is super hot in the failure state.

I see that sometimes the board starts normally, but after a while it returns to the failure state.

From the board schema I see that the voltage regulators 9V->5V and 5V->3,3V feeds the I2C devices. When I've removed all of them including RTC, BT, and disconnected all I2C devices, the error still persists. Do you think that some component on the 1.3 PCB is broken? I've ordered new voltage regulators to replace them, but I'm not sure they're causing the problem.

Do you have any idea what to test next to find the source of the problem?

All advices willl be appreciated!

 

[FelixP]

Hej,

As far as I know, the high current is caused by the big capacitors which you have most probably soldered on the back of the board.

Does any of the capacitors is dented on the top? They should be absolute flat. If not, then they are broken and have to be replaced.

You cannot run the board without the RTC device, because that would leave the I2C bus not terminated and from my understanding this would block booting the firmware. So you can remove the IMU sensor.

Which firmware are you using? Sunray or ...?

Best regards, Felix

 

[slatkowski]

Hi Felix,
thanks for your reply!

Hej,

As far as I know, the high current is caused by the big capacitors which you have most probably soldered on the back of the board.

Are you sure? Maybe in the failure state I have now this could cause the problem. I think in normal operation the curret should be < 1A, because the voltage regulator is able to handle 1A max.

Does any of the capacitors is dented on the top? They should be absolute flat. If not, then they are broken and have to be replaced.

No, they're flat (see the photo in attachment). I've checked other capacitors and they're also flat. The mower is new. I've ended constructing it this spring. The problem occured in a warm (25oC) day, but it persists in a room in my house where I have ~19oC.

You cannot run the board without the RTC device, because that would leave the I2C bus not terminated and from my understanding this would block booting the firmware. So you can remove the IMU sensor.

Ok. RTC inside, all other I2C devices not connected, and I have still the same issue.

Which firmware are you using? Sunray or ...?

I use AzuritBer. But I think the 5V and 3,3V power supply is not dependent on the software (but I can be wrong...).

I've soldered a brand new LM2940-5.0 regulator, and this didn't help. Any ideas?

I think this is a problem with some component on PCB board, but I don't know how to track it.

 

[FelixP]

The voltage regulator is independent of the firmware.

Then I would check all connections if there is a bad soldering. And if they all look fine, then I would take the schematic and start following the power with a voltmeter.