Thursday, March 14, 2013

AV RECEIVER PROTECTION MODE

                                                AV RECEIVER PROTECTION MODE

How to find the fault

First of all remove all the speaker connections from the amplifier. After that power the amplifier and check the protect show or not. If not, then any of the speakers is damaged. If then also it shows protect you have to check the amplifiers hardware.
AV receiver shows protect mode, when there is a hardware fault in side it. It’s a warning that some thing is wrong.
Normally AV receiver’s show this when any of the output amplifiers get some problem. There are six amplifiers in this AV receiver. May occur when the output diver transistors of any of the amplifier become shorted. if the output transistor get shorted this will lead to flow of current through the speakers. To prevent this there is a protection circuit for each channel. One combined output of this protection circuit is connected to the system control. When the any of the output amplifier fails, the protection circuit detects it and switch of the speaker and sent data to the system control. When the system control gets this data it will give a warning to the customer through display that PROTECT. 
You have to check the amplifier. 
For that you need Digital Multimeter, Soldering iron screwdrivers etc
open the amplifier, then power it on. Connect the negative terminal of the multimeter any where in the chase (metal body of the amplifier). Then connect the positive terminal to all the output transistors emitter pin one by one. The voltage should be bellow 0.5V. If any of the emitter of the transistor shows voltage more than 0.5V., then that amplifier stage is faulty. Remove the transistors and check it. if it is shot then replace with a new one. 

After replacing the transistors do not power up the amplifier directly from the main. You have to put a bulb of 60 watts in serial. 
You can do this easily remove the mains fuse. put the bulb in a holder. now you have to wire from the holder. Connect one of it to the one end of the fuse holder and the other wire to the other end of the fuse holder. Why using a bulb is, if there is any further problem in the amplifier stage on which the transistors replaced, there is a possibility of the new transistor get damage. if we use a bulb in serial with its mains supply ,when any overload in the amplifier occur the bulb will drop the current, by lighting itself.
After connecting the bulb in serious power on the amplifier. watch the bulb. It should light for one or two second and go dim. If so check the display, is there is protect mode is on or not. If not and come back to normal operation, then remove the power, remove the bulb insert fuse and check
connect the power and check.
If the bulb shows bright light then there is some component also faulty in the same amplifier section . After removing the power you have to check again the amplifier stage of which the transistor is replaced, for any other faulty components.