Kenwood KAC-729S

[mike49504]

Got this in for repair..

I replaced 2 defective outputs in the left channel..


Amp will not power up.. No voltage on the 1st leg of the power supply fets..

Any ideas>??

 

[Perry Babin]

Post the voltage on the 494.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:

 

[mike49504]

Pin 1: 0
Pin 2: 4.98
Pin 3: 0.07
Pin 4: 0.31
Pin 5: 1.66
Pin 6: 3.66
Pin 7: 0
Pin 8: 13.83
Pin 9: 5.12
Pin 10: 5.11
Pin 11: 13.83
Pin 12: 13.83
Pin 13: 4.98
Pin 14: 4.98
Pin 15: 4.98
Pin 16: 0

 

[Perry Babin]

You should have ~5v on the gates of the FETs.

 

[mike49504]

Ok i fixed that one i had a broken solder connection...


I have another one in for repair also..

when i power the second one up it draws excessive current...

If i only hook power and ground up it will draw excessive current also..

I removed the fets and they all test fine..

Any ideas?

 

[Perry Babin]

Power it up through the limiter and measure the DC voltage on the power supply FETs (black on leg 3, red on leg 1).

 

[mike49504]

I get -3.38 volts on all of them

 

[Perry Babin]

It can't be negative. Are the meter leads in the correct locations in the meter?

 

[mike49504]

Sorry my mistake.. I get 3.38 volts

 

[Perry Babin]

Did you have your probes backwards?

If so, did you have them backwards when you read 0v on the gates?

 

[mike49504]

I found the problem C206 (3900 16 volt) cap was installed backwards from someone else trying to repair it before i got the amp..


Now to put the outputs back in and see what i come up with..

 

[JLH]

Do you already have the service manual? If not I can e-mail it to you. Its too big to attach to a post. PM me if you want it.