Power Acoustic LT1920-2

[caraudioguy2100]

When the board is out of the heatsink it will power up and idle perfectly fine .

Once the board is back in the heatsink it will power up and after a second or 2 it will draw excessive current.

It almost seems like when the secondary ground comes in contact with the heatsink the amp will start drawing excessive current .

Any ideas what might cause this ?

Now the amp seems to do it even with it out of the heatsink

 

[Perry Babin]

Have you tried twisting the transformers to see if they have an intermittent short?

Monitor the secondary ground to see if 12v or a square wave is ever driven to it.

 

[caraudioguy2100]

This is what I get for drive signal on 1 bank of fets .

Any ideas ?

 

[Perry Babin]

Is that with a loading capacitor?

If not, the drivers are likely defective.

 

[caraudioguy2100]

Yes that’s loading the drive with a 0.1 uf cap

 

[Perry Babin]

I think it may be OK.

Do the other banks look different?

 

[caraudioguy2100]

The other bank has a perfect square wave .

The bank in question all the fets bet hot instantly and the amp draws excessive current

 

[Perry Babin]

Are you saying that the other banks have a square wave with the loading capacitor?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

That's not likely unless you're before the gate resistors or the gate resistors are a very low value.

 

[caraudioguy2100]

I dont get it the thermistor had a broken solder connection and I reflowed the solder to 1 pad and now the amp works perfectly fine

 

[barber02]

I had an amplifier similar to that one come into my shop a while back. It had multiple cracked and broken solder joints, particularly on the larger components and the large resistors in the output section, and check the the solder joints for all those jumper wires as well.

I say that to say this. Go over that amp thoroughly while wiggling and moving components and looking at the solder connections on the bottom of the board.

David

 

[Perry Babin]

I agree that there is likely a bad connection. There is no way that the thermistor connection could affect the drive signals.