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I think a have an explanation, and You will not like it. Don't measure voltage, just check "short" connection by multimeter. Remove RAMPS and Arduino out of the printer. Disconnect it from everythig and remove drivers. Use it to check the GND pins under the drivers. If you will find them "disconected" from "-" on PSU clamp or USB cover (no short detected) than the pins or traces on RAMPS burned when the drivers were set to Vref 1.6V = 3.3A.
If that is the case, remove RAMPS out of Arduino and check it from the bottom side. If you can measure short between soldering of GND pin and "-" on the clamp, traces are good and the pins are gone otherwise you will have to find where the trace is interrupted.http://domoticx.com/wp-content/uploads/2017/05/RAMPS-Shield-1.4-print-layout-beide-kanten.png
If the GND line on RAMPS is OK, GND pins (just the pins) on your drivers are gone. You can check them separately by checking short between tip and soldering.
Anyway you will have to solder a bit or buy some new parts.
EDIT: Last thing I can come up with is that the RAMPS is not inserted into the Arduino properly or some pins are gone there, as it is strange you cannot measure Vref across trimpot and USB cover and there is not 5V on Fault pin of the driver.