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

For $800, if you like the amp, it may be worth paying a tech to diagnose; otherwise, it's practically worthless.  

If you cut your losses, you can start over and find a really good amp under $2000 used.  

Just ask and you'll have responses coming out of your ears.  You could start a thread, "HELP BUILD ME A SYSTEM FOR UNDER $XXXX.00"  There's ALOT of us who have been around long enough to remember great amps from the 80s and 90s that's still great today and built like tanks--stuff I drool over today.

you can start over and find a really good amp under $2000 used

that sounds reasonable but I didn't buy an amp for $800 because I had 2K. For now I just have to figure out how I can get a working amp. I can stay near $800 if I can sell this amp for $400

For now I just have to figure out how I can get a working amp.

@parkergetdean you have a working amp. Just don't turn it off is all. Keeping it on 24/7 is what real audiophiles do anyway. What kind of person turns their gear on and off? That's how you get a broken switch!! Please.

What kind of person turns their gear on and off? That’s how you get a broken switch!! Please.
 

Lol

all jokes aside, that amp consumes about as much as a 100w light bulb if left on 24/7. Just don’t say nothing to nobody about your significantly increased carbon footprint. You don’t want the California authorities knocking on your door…

You probably already know all this but based on the symptoms you've described for your Musical Fidelity A308 the problem is likely a failing DC protection circuit or deteriorating electrolytic capacitors in the power supply or output stage.

Likely Causes:

• Leaking DC Voltage: The "popping" sound upon startup is often a surge of DC voltage hitting your speakers. In a healthy amplifier, a relay delays the speaker connection until the internal voltages have stabilized. If this relay or the sensing circuit is failing, it may allow a DC "thump" through or, conversely, detect a fault and immediately trip the protection mode.
• Capacitor Degradation: The A308 is known to have issues with original capacitors leaking or losing their ability to filter surges as they age. When these capacitors are cold (first thing in the morning), they may struggle to stabilize, causing the pop. Once they have "charged" or slightly warmed up, they might fail to discharge properly or maintain a stable state, preventing a successful restart.
• Protection Circuit "Lock-out": Modern high-end amplifiers like the A308 have sophisticated protection circuits. If the amp detects a DC offset or a thermal anomaly during that initial "pop," it may enter a "Protect Mode". The fact that it won't turn back on for hours suggests a component is staying "latched" in a fault state or is failing to discharge a residual voltage that the protection circuit interprets as a persistent short.
• Transistor Instability: This model uses specific Sanken Darlington transistors which can be fragile. An internal failure in one of these could cause the midpoint voltage to drift, triggering the protection relay to stay open (preventing power-on) to save your speakers from damage. 

Immediate Troubleshooting Steps

1. Disconnect Speakers: Try turning the amp on without any speakers or source cables connected. If the "no-start" issue persists, the problem is definitely internal to the amplifier.
2. Check for DC Offset: If you are comfortable using a multimeter, you can check for DC voltage at the speaker terminals (with no speakers connected). Anything above 50-100mV is a sign of trouble.
3. Visual Inspection: If you feel safe opening the chassis (unplugged!), look for "bulging" or "leaking" capacitors, which often look like they have a crusty residue at the base or a domed top. 

Note: The Musical Fidelity A308is a high-voltage, high-current device. Because it is a "legacy" high-end component, it is highly recommended to have it serviced by a professional who can "re-cap" the power board and reset the bias to factory specifications. 

FYI - I have an NAD 275BEE in great shape that I would send to you to try it out, or purchase. Only ask $300 for it. I don't have the original box, so it would take some time for me to get a box and pack it properly, but I thought I would throw it out there as an option. 

Here are the specs:

https://www.crutchfield.com/S-ekCVFS5408T/p_745C275BEE/NAD-C-275BEE.html?XVINQ=D74&XVVer=6F3&awcr=632463186226&awdv=c&awnw=g&awug=9007356&awkw=dsa-823367458691&awmt=&awat=&gad_source=1&gad_campaignid=18795435785&gclid=Cj0KCQjwgr_NBhDFARIsAHiUWr6pUODI0gt67OmFdUlnF5YNCSFGtZN9SaYdv0SQkmyWBzYJb1kIipYaAs6yEALw_wcB