^You also swapped channels on the outboard power amp to verify it isn't that channel of the amp?
Repair centers which are also retailers are often jerks about fixing stuff they didn't sell you. It is childish, immoral, and illegal, but it happens. It is their way of getting back at you for buying elsewhere.
If you can't send the unit to Marantz directly, I'd look for another repair center.
Testing to see if the front Left channel is dead from the internal tuner also, verifies it isn't a problem with the AV7005's input section. Try that.
The repair ticket must be worded with this percise, specific level of detail [for example]:
"Using the DVD input,
with analog RCA connections,
in stereo mode,
Audyssey and all other effects off,
Pure Direct off,
the front left channel output is very, very faint."
If a diagnostic tester dude isn't replicating exactly the way you use it, it could be that's why they are reporting "NPF".
Ideally, lug your source machine, interconnect wire, power amp, speaker wire, and one small speaker to the shop to demonstrate it actually not working, in person. Call ahead and explain you will be glad to do all the connections yourself and all you are asking for is to use an AC outlet they have and have them listen to it once you've set it up.
Testing to see if the left headphone jack out is faint also may help prevent you from having to lug anything beyond a pair of headphones to demonstrate the problem.
Edited by m. zillch - 10/27/13 at 10:11am