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.