No 5V and 3V3 on Duet3 6HC

Krzysztof

Hi,
my new Duet3 6HC board has developed an issue that affects its opreation. It happened when I was testing PWM outputs on OUT4 and OUT5 with different frequency settings. After few iterations of turning off and on board's power, I could not connect to the DWC. After inspection I have noticed that STATUS, ACT, 5V and 3.3V status LEDs are dark. V_FUSED and 12V status LEDs are on. From my point of view it looks like the 5V step down converter chip is the problem. It outputs voltage in the range of 1V.
Same problem occurs when I connect the board to my computer with USB-C cable (without connecting VIN).

I was powering my Duet with 24V from laboratory power supply. Duet was running on RRF 3.4.6 (or 3.5.2, I can't remember exactly as I have several main boards with different fw).
I have installed more than 10 Duet3 6HC boards without any issues. This is the first time when any problem with Duet board occured.

Can I check something more and what can I do next?

Best regards,
Chris

droftarts

@Krzysztof Sounds like the 5V voltage regulator has failed. You can disable the 5V regulator in case it has internally shorted (see https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Mainboard_6HC_Hardware_Overview#h-5v) and try and supply 5V externally (eg via USB), to see if 3.3V comes on, and check nothing else has failed. Is it possible you shorted 5V to ground when testing OUT4/5, or fedback more than 5V onto the 5V rail? It may be possible to repair it yourself, there's a list of the voltage regulators here: https://docs.duet3d.com/en/User_manual/Troubleshooting/Parts#voltage-regulators
Otherwise, it's probably a warranty replacement.

Ian

Krzysztof

@droftarts I have followed your advice and connected external 5V supplied to 5V_EXT connector. The current was from laboratory supply set to 5V and current limit of 0,5A. It looked like there was a short circuit as the board drawn full 0,5A from the supply. I have immediatley disconnected the power but have noticed that 5V and 3,3V LEDs blinked for a moment. I have repeated the test two or three times until a smoke appeared near D33 and U22 but after that a very strange thing happened- 5V and 3,3V LEDs turned on. Next I have connected 24V to VIN and the board is alive and connects well.
Do you know what could happen? I'm confused

Chris

droftarts

@Krzysztof D33 is an ESD protection diode:

U22 is part of the USB circuit.

See the schematic here https://github.com/Duet3D/Duet3-Mainboard-6HC/blob/master/Duet3_Mainboard_6HC_v1.02/Duet3_MB_6HC_Schematic_v1.02.pdf

I don't know why these have blown, but at a guess they've burnt out because of the short, which now doesn't short. However, this probably makes repair difficult. I think @T3P3Tony or @dc42 will need to advise you further, but probably unplug it before there is any more damage!

Ian

Krzysztof

Hi @droftarts, the board is unplugged, and I'm waiting for further instructions. From what I can see, there's no way for me to solder the element manually- it's too small and too close to other components. I'm not sure how D33 could have shorted, as I’ve been very careful when handling the electronics. Either way, it happened

Chris

Krzysztof

Hi guys. I would like to ask @T3P3Tony or @dc42 for further instructions.

Chris