Tv wont switch on. i have a onn lcd tv it wont switch from standby transformer is a 12v 5amp i

Question

i have a onn lcd tv it wont switch from standby transformer is a 12v 5amp i plugged another transformer in and worked i just need to no which part of the transformer is faulty so i can replace the part,the broken transformer lights up the stand by light but will not boot up the tv when pressed to switch on can you help the transformer model is