Dear Sir,

I have this car amplifier 'US amps' which is going into protect mode. It is using tl494 pwm IC.

The pin 16 was going high 12v. so i removed the connection going to the pin and the amp started good. when i removed the connection and checked the voltage on pin 16 and it was still showing 0.8v some times 1v and some times 0.6v. it suppose to be 0v without any input. why is it showing some voltage. what about be wrong? somebody please show some light on this. thank you in advance.


Regards,
Imran

 

The TL494 is a pwm switch mode ic, pin 16 is an (+)input for the op amp, pin 12 is the supply, chances are its being pulled down by a mosfet or rectifier diode on the pulse transformer outputs.

Datasheet
https://www.google.co.uk/url?sa=t&s...gghMAA&usg=AFQjCNEbDmPLD_FQdbVwnFHAMHJoDMtfYQ

 

Dear Sir,
How to find which mosfet is pulling it down. it have total so many mosfets. what about transformer? when i force to ground the pin 16 i am hearing some kind of sound near transformer side. not sure if it is transformer or mosfet. how to find the place where it is pulling down.

 

You need to measure the voltages in the circuit first, ideally get a circuit diagram of the car amp.

 

I dont have circuit diagram. it is not available in the net.
even though i remove the +input it is still showing 0.6v and also pin 3 is 4.6v which is high also.

when i remove the connection of pin 16, pin 15 is 2.6v and pin 16 still have 0.6v. dont know where it is pulling. where is the short? all the mosfets looking good.

 

You aren't going to be able to repair it without a circuit diagram easily, you're going to have to make voltage tests and post pictures of it, otherwise bin it!

 

My first suspicion would be that the shorted component is in the audio output side of the amplifier not the power supply side.

A shorted switching mosfet on the power supply would give you an instant dead short resulting blown fuses or blown up mosfets when you hooked it up to 12 volt power.

A sort circuit the audio amplifier side would cause the power supply to go into protection mode since a short circuit there is something the power supply has some degree of control over.

 

i removed all the mosfets and i am still having the same readings. nothing change. so it is not mosfet. and i have checked output transistors but nothing is short. also rectifiers are good too.