NAD 7140 repair-HELP

I recently picked up a NAD 7140. When plugged in it lights up and the relay audibly clicked, but no sound from any source or from headphone jack. I found the preamp does work with another power source. I understand that NAD products have had reliability issues. So, is anyone out there aware of a common fail in this line of receivers, where is the first and best place for me to check? I will try DIY repair as well with some direction, where to start? I don't see any obvious leaking caps or fried resistors. I also cleaned pots, buttons, and connections with electrical cleaner. One last thing, when I opened it up there were two slow burning fuses burnt out, neither being the main power fuse. I replaced them and they held when I turned the unit on. I may sound like I know what I'm doing, but I am brand new at tackling a self diagnosis and fix. I do find it a challenge that I want to take on and learn something along the way. I have scoured the internet for answers without any success.  
I hope someone in this community can help and give direction.
Thank you!
Sorry if this sounds like a dumb question, but just need to make sure you are not missing the pre/main jumpers. When you tried the preamp with another amp, did you have to physically remove a jumper between pre out and main in on the 7140 like the ones shown in this picture.

Those jumpers are required for the 7140 if it is only used with speakers and a source.

The jumpers were in fact present plugged in, then removed to test preamp section. 
Thanks for responding, any other thoughts...
Make sure the tape monitor  button is not engaged!
Those fuses for tuner section only.
If both channel of Amp section not working, start with power supply to diagnose. You can download service manual from
Thanks, it's good to know what those fuses are for.
I did download a service manual. I'm not a tech, and after looking at it I am absolutely certain I do not know what to do😁.  Is there a laymans step by step guide to identify component, test proceedure, multimeter settings, expected voltages, etc? A pictorial or a video? Again, I have scoured the Internet and cannot find what I am seeking.
Thanks again
If I were you, after cleaned the speaker selector, relay contacts etc, if the amp section still not working, I will leave it as is, find a cheap used Adcom, B&k or Parsound power amp to pair with it.
Again, please make sure the receiver is unplug from the AC outlet before you working on any thing inside.
Thanks for the link and precaution. I will not fry myself!!! But, I must continue on this journey until I succeed or at least gain understanding of basic troubleshooting.  I like reviving the broken...
wish me luck!
I will post when I succeed.
Did you ever find a solution to your 7140 with no sound output?
I'm in a similar situation with a 7130 with no sound output (albeit very minimal output on full volume)

I've sprayed everything with contact cleaner, and can't see anything visibly wrong, but I'm desperate to find the problem.

Let me know if you did manage to sort your 7140, and if so, how!

Many thanks

Dump this unit and get something good.