FYI. Raspberry Pi CM4 with 5V to Gnd Short

People may not be familiar with BTT’s Manta controller boards - they have a built in 5V power supply and sockets to take a Raspberry Pi CM4 to eliminate the need for a separate 5V power supply and wiring in your Klipper system.

In trying to setup a Manta M8P, I inadvertently used a fresh out of the box Raspberry Pi CM4 that has a 5V to Gnd Short. The CM4 is part number CM4101000 which means it has a WifFi module (external antenna required), 1G of DDR and no eMMC Flash (also called the “Lite” version).

When I put in the CM4, none of the expected Raspberry Pi LEDs came on and the fan LEDs flashed about once per second. I left things running for a total of about five minutes, after which the Flashing LEDs stopped and when I checked the 5V supply on the Manta, the voltage was 0.1V.

In looking at the situation, I discovered that the resistance between 5V (measured at the VUSB jumper pins on the Manta - the VUSB jumper was never installed) and Ground was 0.2Ohms higher than lead resistance. After removing the CM4, the resistance was infinite - which was also not good as when I applied power to the Manta, the 5V supply was dead.

There is no visible damage/problems with the two 100 pin connectors either on the Manta or the CM4.

When I look at the TPS5450 datasheet, the 5V regulator chip on the Manta, I see that it has a “hiccup mode” which turns off power when it encounters an overcurrent condition and then restarts - which explains the flashing LEDs. Unfortunately, I seem to have left it running for too long and I burned out the TPS5450; I may attempt to replace the chip but it has a large thermal pad on the bottom which makes hand repair difficult (I do have the right tools to replace it, it’s just “difficult”).

Fortunately, I had a spare Manta and CM4 - checked to see that there isn’t a short between 5V and Gnd, put them together and things seem to be running fine.

I’m putting this in for information in case anybody has a similar problem. It might be worth checking the resistance between 5V and Gnd on a Manta/CM4 combination before applying power.

Interesting, thanks for the heads up!

I run a couple of these manta boards and a bunch of the CB1’s on their own, so I will have to make sure I keep an eye out for anything fishy going on.

Thanks again,

1 Like

Is the 5v supply that you fried only used to power the Pi? If so would you be able to power the CM4 through its GPIO pins? There would be some advantages to being able to have it powered independently from the Manta.

The 5V supply is also used by the Manta.

I don’t see any advantages to this when I look to using an Octopus/Monster board with a Raspberry Pi that is powered separately.