I think with these all the lights come on when power is first applied, then they go out almost instantly when the SoC starts to run. Except the power LED, because it is connected directly to the power supply rail and not controlled by a GPIO.
If you don't get anything on serial look for any activity on the SPI lines to the flash chip.
If it isn't even trying to load the bootloader out of flash it is very likely a hardware problem with the RAM. Check for adjacent pins shorted. Check for the 2.6 volt power supply, the 1.3 volt reference voltage, and the clock signals.
That is the right chip to use. 512 Mbit = 64 Mbyte. I have installed several of that exact same chip.
Part of the part number is 12 = 512 Mb, and 16 = 16 bit data bus.
The 2.6 volts comes from Q3. It is a simple PNP transistor linear regulator drawing from the +3.3 V bus. There is a circuit inside the SoC to drive the base of Q3 and regulate the voltage. It is not adjustable.
Is any part getting hot, Q3, the RAM, the SoC?
Also with the power off, put your meter on diode test and walk the leads down each side of the RAM chip testing for adjacent pins bridged together.
Thanks for your support. We reattached the old 32 MB RAM, but there is still the same picture of the behavior of the RE730 v2....
I guess maybe it's unfortunately really broken during attaching the new chip via hot air gun.
Now we're struggling to proceed with my Mr3220 v2, WA801 and WR841v8.
As far as I understood, it should work to replace RAM with all of these devices, don't we?
Any suggestions how to proceed? - How did you succeed? I was also thinking about just trying by soldering, but you need to put a lot of soldering material and I get short circuit on the chip... I'm actually struggling now what to do because I let this already do from some professional people who do this already for 30 years and it unfortunately failed...