Ughh, It took me about an hour to decipher what you said.
lol i try chinglish here, fewer words to get the most infos... i tried standard english (longer words) people dont understand me anyway. dig deeper into the circuit may reveal some of the senses...
1. The bottom left TO-220 packages are YG225D2 and obviously(now after my scratching my head for an our) on the secondary side of the transformer.
yes refer to 1a.png below... a bit strange you have 2 rails for each Vcc and Vee, 4 rails all. the few i repaired only 2 rails, so i had the green rectifiers removed only (i guess thats the 2 black chips on the bottom on pcb. now you have another rectifiers purple in picture, but i guess thats for low powered rails to feed drivers and 15V ic's.. i draw each side secondary and primary for you so you dont have to watch hours of youtube video that usually have many unrelated rants to figure out what... red are highly suspects, those 4 mosfet top left on your pcb, have them removed all and checked/replaced for damage status. yellow are mosfet driver or protection something, less likely to be damaged, blue is the heart of smps TL494 (Vac that you have a headache of how is generated) very less likely to get damaged. you can probe those pins output to have square signals, if not, that probably dead and no power no over current warning, not your problem. your problem is dead short, have that red color mosfets checked asap.
According to the schematic it looks like these rectify the L&R +33/-33V rails?? There is a 5T:12T transformer just before so i assume 14V from the car battery through the 5T:12T to get 33V?
??
yes. thats the big toroidal transformer you are talking about, very hard to miss on the board. thats the heart of the power.
(though i havent figured out where and how that is getting converted to AC before being sent to the transformer yet)
you can study later it can be wonderful thing how 12Vdc can get electrocuting high voltage Vac on the output. but first you have to make sure components are ok first, check the red color and then we can continue talk.
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2. The 4pack of fets in the top left are FQP50n06. all the gates are being fed by pins 9 and 10 of the TL494CN (this chip i assume sets up the PWM carrier of a class D amp?)
yes thats what we keep talking about, have that checked. no, its not for class D amp, your amp is AB only (no digital), class D is different beast, but only difference on secondary side, primary side still the same as your AB, the PWM is what makes Vac, for higher rails to feed your class AB (and D, not yours) amp on secondary side.
3. These guys are TIP 35(6)C's and they carry an amplified sine wave from the +/-33v rails to the speakers??
now you bring us to secondary side, refer 2a.png... red are those tip 35/36 pair giants (red colored) have those checked as well, another highest suspects on secondary region. forget about me talking to isolate secondary side. have them all checked is the easiest without moving a brain cell (all the red colored, and then later green and purple rectifier all those are hard to miss on the pcb, the all black box transistors 3 legged alike).
I wasn't lying when i said it's been a LONG time since doing any electronics work at all.
you ask dave to repair tv or something else he can get nuts. different device needs different experience to repair. we have people here expert in digital or RF, but know rat arse about power electronics. vice versa. this is very broad field, some are highly specialized into one area, some are jack of all trades, but not so expert, only armchair keyboard warrior like me
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