I have a Turning Pi 1 that I am getting my money's worth out of 🙂 Currently it has seven CM4s blades in it with memory capacity from 1 to 8gb and runs very well. However I've always wanted to get a RPi5 running in one of the slots. Which is a problem as they have not released a CM5s board in the 200 piun SODIMM factor. Well, now I have a CM5 module running in a Waverunner board. Hurray! The problem is power: It looks like the Waverunner board sources power from the VBATT signal on the CM3 side which in the Turing Pi is 3.3 volts. 5 volts is on the various GPIO pins, but that's sourced from the +5 regulator on the TP1 main board. The on-board 3.3 to 5v boost converter (the Pi5 compute module wants +5 input) either doesn't have the power or is not configured properly and as a result things don't work. Boo. So instead I hot-wired a connection from the +5 on the GPIO pins right into the Waverunner's +5 line after FIRST removing the zero ohm resistor at R6 or R7 and tying a wire into the TOP of R7. I first tried a 24 gauge wire-wrap wire and the light on the board lit up, but then went out. I think the CM5 detected an undervolt. I then used an 18 gauge wire and it's UP! So far: HDMI video does NOT work. This sucks. The board's wireless DOES work (it's a wireless equipped CM5 as I didn't know if ethernet worked The board is booting off an external memory card in the TP1's slot. So that DOES work. THE ETHERNET IS UP ON THE BOARD!!!!!! HOLY SMOKES THAT WORKS! I'll play with other stuff like the USB and such later. A big question is does the Ethernet run at 100mbps or 1gbps. Technically the switch in the TP1 is a 100/1gb switch and it would be REALLY COOL if I could run RPI5's in there at 1gbps. More later, but it can be done.

Hi @cz, nice project and hacking on the TP1. Mine is collecting dust ATM because i moved to the tpi2, but one question. I think the adapter plates used are these ones. Could you confirm that? https://www.waveshare.com/product/raspberry-pi/boards-kits/compute-module/cm4-to-cm3-board.htm

Yep. See that 0 ohm resistor on the left? That needs to be taken off and the +5 supply needs to be tack soldered to the top of where it was. That will feed +5 directly to the DC-dc converter on the waveshare board which will provide properly filtered power to the CM5 itself.