Targa 2.8kz staying in protection

[Aqeeb127]

Hi im busy with a 2.8kz targa but its staying in protection ive checked outputs and drivers amp builds rail voltage then trips in protection any ideas what it could be thanks in advance. Pics will be taken tomorrow if need be

 

[Perry Babin]

Photos?

 

[Aqeeb127]

Hi i dont know how the quality but if need be i shall retake the photos

 

[Aqeeb127]

I also found burnt resistors but the power supply drive circuit by the buffer transistors i think it could be those that is causing the protection to kick in and i dont know the value it should be

 

[Perry Babin]

See if this file is close.

 

[Aqeeb127]

Thank you very much you are a star. Its almost exactly the same

 

[Aqeeb127]

Is it ok if Q7 and Q8 is replaced with bd139 and bd 140
And the power supply mosfets are replaced with irf3205

 

[Aqeeb127]

The amp was repaired by someone else and now im sitting with this problems

 

[Perry Babin]

You can/should use the BD transistors. Mount them well off the board and solder top and bottom. Replace all 4 PS drivers. If the remaining good drivers that you remove are still good, save them if they're hard to get from your suppliers.

 

[Aqeeb127]

Thanks but those transistors are in but its still going to protection

 

[Aqeeb127]

As soon as the rail voltage builds the amp shows the power on light for less than a second and then hits straight into protection with no output mosfets in

 

[Perry Babin]

Try installing the PS FETs but remove the rectifiers. Will it power up?

 

[Aqeeb127]

I am going to remove them quick

 

[Aqeeb127]

Yes it does power up with the rectifiers out

 

[Perry Babin]

Were any of the output transistors shorted?

Do you have a current limiter for your B+ line?

 

[Aqeeb127]

No mosfets shorted

 

[Aqeeb127]

And no i dont have a current limiter im using a 12v 3amp supply

 

[Aqeeb127]

There are no mosfets in the output section as i checked them out of circuit just in case and used the lcr tester to make sure

 

[Perry Babin]

Reinstall the output FETs and check the drive signals while the rectifiers are out of the circuit. With NO rectifiers and therefore no rail voltage, you can check the drive with the scope ground connected to the source leg of the FETs.

 

[Aqeeb127]

I dont have a scope yet is there any other way i can check it