greetings companions I get this equipment with the failure that does not turn on, check the source and the sub-transformer comes out 15v that go to transistor q5721 and there the voltage dies, so I do not feed the regulator ic 5701, I guess it You are protecting for some reason and have not yet managed to find the cause of the problem. Friends if any of you have been presented with this type of failure and can guide me I will be grateful. I hope your valuable and prompt response friends