I just searched for any help for my just bought MDS-JE480, it was described as "dead not working" and stumbled upon this page, so I would like to add this information for future reference:
I had these symptoms on a MDS-JE480 - no standby light, one or two clicks from the power supply relay when I plugged it in.
Checked all voltage regulator transistors, they all showed all the correct voltages.
So I swapped the transport with a known good one from a working deck, the unit powers up and works just fine.
Put the transport from the (apparently not) dead deck into the good deck: again, the good deck shows no standby lamp and is dead.
Ok, I thought I will change the infamous loading belt: again no change, still dead. (By the way, it is between 1-1.2 mm square profile, 17mm diameter or 30mm folded length)
So something's amiss on the board under the transport: Someone had re-inserted the flat cable in the wrong place, between the circuit board and the plug itself! Put the flat cable back in the plug's slot, problem solved.