MTX thunder 2300x

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Hi Guys
Im fixing a thunder 2300 and i am having an issue with it powering up ,i have checked and replaced all the faulty FETS (supply and outputs) ,checked the RECT(all good) there are no signs of damage to any resistors or capacitors that i can see but when i apply power all i get is the fan running and no power light the left and right channel is producing nothing also, just need some help with what to look at next or if someone has come across this problem before i start checking all the diodes and transistors. the board is marked TA2300X REV F.
 
these are the results i got not to sure if you required it to GND or +12 so i have got both ,supply voltage is 12.55v

Pins to GND Pins to 12v+
pin 1: 0.604 pin 1: 11.940
pin 2: 2.276 pin 2: 10.270
pin 3: 0.060 pin 3: 12.490
pin 4: 2.357 pin 4: 10.21
pin 5: 0.469 pin 5: 12.09
pin 6: 0.998 pin 6: 11.56
pin 7: 0.003 pin 7: 12.55
pin 8: 12.37 pin 8: 0.081
pin 9: 0.003 pin 9: 12.55
pin 10: 0.003 pin 10:12.55
pin 11: 12.37 pin 11: 0.181
pin 12: 12.37 pin 12: 0.183
pin 13: 2.370 pin 13:10.91
pin 14: 2.370 pin 14:10.91
pin 15: 2.370 pin 15:10.91
pin 16: 0.004 pin 16:12.55
 
The list was provided so you could copy and paste it.

Please read the basic repair page on the car audio site. It states repeatedly that you use ground as the reference (black probe).

The IC appears to be defective. Pins 13-15 should have 5v.

It could be that something is dragging the voltage down but without a schematic diagram for the amp and considering how complex it is, it's probably easiest to replace it.
 
No not at this stage im just starting with the most common problems first ,the amp is drawing 0.79 amps which appears to just be from the fan when tested with a dc clip on meter, i will do more testing before i order in a new IC or anyting else i dont want to replace it if it's ok (looks time consuming)
 
Just posting what i have done so far .Removed IC 494 first,tested all ok fitted back into board and removed anything that come of pins 13,14,15 followed that circuit and found when i removed transistor Q409 my voltage when back to 5v ,tested transistor all ok so followed the cicuit back to the other side of the board and found diode D404 faulty ,fitted new diode voltage is now stable so will reinstate everything and see if amp powers up.
 
found more faulty components this time it's transistor Q412 (2N6491) which i can get from mouser but transistor Q425 (MPSW56) i am having difficulty finding a replacement ,has anyone got suggestions on a replacement as this is an obsolete part i have looked at other data sheets and are unsure what to use that will work with out damaging the amp
 
is it stiil ok to use that transistor compared to the original MPSW56 as the collector current is only 0.5A instead of 1A and the VCBO,VCEO voltage is -80V instead of 80v does this matter im only a newbe so i am unsure ,i did have a look at a ST micro electronics tranistor (STX817A) ?
 
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