AMp does not display any LED read out

Sounds like it's overheating or otherwise overloaded. Check the front panel channel status indicator to see if it's a heat issue (hot vs. norm). I'm guessing there's a short at the output that's putting it into overload after 1/2 hr.
http://www.mackie.com/pdf/M800_om.pdf

i) I assume the fuse you mentioned was in the mains plug - did you also check the fuse in the TH15A mains input socket? This is accessed by pulling out the tab in the bottom section of the socket (below the centre pin). This is a 3.15Amp antisurge fuse, 20mm type.

ii) If this fuse has blown, then replace it & all may be well ...... but if it blows again, then move to step iii).

iii) With mains disconnected, remove rear panel (outer screws) & check the power supply PCB for damaged components, especially R111 & R112 (100ohms). If the latter are burnt or open circuited, then the amplifier module may have blown.

regards, Dave

Sorry to hear that you have been the victim of a common plague associated with the inter spa.
if your unit is no longer in warranty then you will have to buy the new head. The head being the part held in place by the three hex socket screws.
Remove the screws, lift the head and unplug the harness, when the new one arrives just install in reverse order.
this happened to me and my replacement head is still going strong three years later.
look up intel parts on the internet and find the part you need and order direct.
my replacement head cost $34 then.

Most likely this is a broken lead on one of the 15 volt buss regulators. Very common problem.

Replace transistor Q91 with a 2SD1264A transistor.
Replace resistor R205 with a 10 ohm 1/4 watt resistor.

These will be located on the small board that the fan plugs into.

This is a fairly common problem with this amp. Parts can be found on the net for a few bucks. The shipping is usually more than the parts.

This probably means there is a failure and the internal protection circuits have activated. It will probably have to go to a shop for repair.

check the grounding resistors, 300-470ohm 5 watt, big ones. they may need to be resoldered to the board, they get hot and break solder we;ds as they cool.

missmatched impedance, insufficient ground, blown transistor.

check the solder joints from the fan to the board and if they are fine u will need to get a new fan

chenge battery