amp I bought 3 days ago not powering on - electrical engineer advice wanted

All these people suggesting returning the item should give that a second thought.

I'm not sure how many times the OP used the amp before it quit, but he says "played it every day, worked fine".

So let's just assume that means a week. Are you seriously saying that if a piece of equipment you sold breaks down in a week, you are on the hook for it? It's a used amp, and I'm guessing it's at least 20 years old. To me the typical bar for used sales is that it works out of the box. Or at least it doesn't break during the first or second use. What is the implied warranty on a used item if not specified at the time of sale?

He can go back to the seller and ask for compensation, or whatever he's willing to do. But I don't think he's on the hook for it.

A refund on a cash purchase on Craigslist, that worked on delivery, is quite unlikely. Though can’t hurt to ask...Hopefully you only paid a few hundred...I’ve been surprised how many desirable items (and yours is), that are not working, selling for good prices on ebay....probably techs who can tell what’s wrong and repair it themselves...on a 20-25 year old high powered amp never know ...

it's going to most likely be in the turn-on mute delay circuit based on your description of the issue.  It would be difficult to troubleshoot without schematics.  I always suggest taking a peek inside your equipment, problems or not.  There are some extensive threads on a DIY board re this particular amplifier. Searching and finding that might threat give you some insight or lead you to someone who might be able to assist. 

Let us know what Musical Fidelity says...

@seasidelps thanks! I know that if I open something and touch it, it will likely stop working. I want to avoid a $350 service bill. But all this info from you guys in empowering!
@ozzy62 @jl35 

I paid $800. I have no regrets. 

I sold my less powerful amp 2 weeks ago on USAM, tracked the shipment, followed up with him immediately if it arrived unharmed and the buyer said it was all good. 2 days later he emailed me that it had a humming noise when turned on. He wanted to send it back. 

I asked him to check a few things and move it and see what is humming. Never heard from him ever since, I assume the humming wasn’t a flaw in the amp. But I was sweating. 

Since my current amp WORKED for 3 days, and then it gave up, I don’t think I have ANY moral ground to return it. If it was new under warranty, then I sure would. 

I don’t think I could get a 150Watts amp for twice this price, this quality, new.