mtx 4250d powers on but lights out when sub hooked up

[ford06f150]

amp powers on. led red but when i hook up a sub to any speaker port sub cone sucks down and i get a thump and a hum or buzz. cone stay pulled down and led goes out but as soon as i unhook subs led goes back red. very new to this how do i tell whats output or input transisitors? i see theres is 6. i know 2 for in 2 for out but not sure on other 2 i did find one that did not move my muliti meter so i took it out. saw a youtube video where a guy took out the bad ones and tested it with them out to see if it helped and it fixed it. that way u can see if thats whats doing it and it worked for him. i still get the same with it out. thanks shaun

[nigelwright7557]

The output transistors are the larger ones.

Could be an output transistor(s) gone.
They usually go short S-D or C-E.

[ford06f150]

i saw that in my other amps but this one they are all the same in size. any one know how to test them with mulimeter. there are 2 next to the speaker outs guessing thats them. thanks shaun

[nigelwright7557]

Originally Posted by ford06f150

i saw that in my other amps but this one they are all the same in size. any one know how to test them with mulimeter. there are 2 next to the speaker outs guessing thats them. thanks shaun

Test them with a multimeter on low ohms setting.
There shouldnt be a short between any two pins.

[ford06f150]

on one my meter does nothing acts like im not even touching anything no mater witch 2 its on. other it jumps up and drops fast no mater witch ones its on. thanks shaun