Sundown SAZ3500D

[caraudioguy2100]

Yes the outputs were in circuit

 

[Perry Babin]

Do you have clean audio, without any significant DC, from the op-amp that's feeding the driver board?

 

[caraudioguy2100]

I don’t get this amp .

If I put outputs in locations Q16,15,14,13 the amp goes into protection even without the driverboard in the amp .

I know the outputs are good since they are brand new outputs .

I can have all the other outputs in the amp besides the ones I listed if I do then the amp protects .

Any ideas what might cause this

 

[Perry Babin]

Does the DC voltage measured from gate to source on those FETs remain at 0v when you try to power up the amp?

 

[caraudioguy2100]

No when powering up the voltage goes up to 35 volts between gate and source

 

[Perry Babin]

With no driver board, how are they being driven? Follow the circuit back (FETs out of the circuit). If you can't find it, desolder all of the gate resistorf ro those outputs to see if the problem is coming from before or after the resistors.

 

[caraudioguy2100]

The amp has no outputs and no audio driverboard in it right now .

With the gate resistors removed the voltage between gate and source pads remains at 0.00 volts

 

[Crazylogix]

Do the output fets have pull down resistors? If not when you install them without a driver board they can get turned on and go boom.

 

[caraudioguy2100]

With the gate resistors pulled the voltage remains at 0

 

[Perry Babin]

Do the gate resistors now have DC voltage?

Black probe on the source pad for the FETs?

 

[caraudioguy2100]

Yes now the gate resistors have voltage on them

 

[Perry Babin]

With no driver board, where is the voltage coming from?

 

[caraudioguy2100]

Not sure I will have to trace the circuit back now and see where the voltage coming from

 

[caraudioguy2100]

I found the problem .

The board became conductive under a capacitor .

Cleaned the board scraped out the section of board where it became conducive and now the voltage remains at 0.00

 

[caraudioguy2100]

Ok amp is all back together and powers up and idles fine .

Now the problem is I get no rail to rail oscillation on the outputs.

Any ideas where to start looking ?

 

[Perry Babin]

If you drive a strong test tone into the amp, do you get any sort of drive at the gates of any of the output transistors?

 

[caraudioguy2100]

No

 

[Perry Babin]

Do you see signal on:

The input to the driver board?

The output of the TL072?

The output of the LM211?

The input to the driver ICs (pin 1)?

 

[caraudioguy2100]

Do you see signal on:

The input to the driver board? Yes

The output of the TL072? Yes

The output of the LM211? Yes

The input to the driver ICs (pin 1) No

 

[caraudioguy2100]

Amp is up and running finally .

U1-KA78T12. Was defective .

I wanna thank you for taking the time to help me with this repair.

I greatly appreciate it !