Twisted Sounds 8.5k

[Perry Babin]

That's better.

Now try it on the output FETs. Remember, you won't ground the scope to anything but the 12v PS (like it should normally be connected). For the probes, you will only touch the tips of the probes to the circuit.

Post photos of the drive waveforms.

 

[mnhiphop101]

Ok that's high and low side

 

[Perry Babin]

Did you have the 'negative' scope probe on the source leg for both waveforms? It looks like one was reversed.

Are you driving a signal into the amp?

 

[mnhiphop101]

Yes I am driving 100hz sinewave into it

 

[Perry Babin]

Are you losing input signal?

I don't remember ever seeing the drive from a 21844 do that.

 

[mnhiphop101]

I'm back working on this amp again. When I install the output fets I lose drive and have -28vdc on the speaker terminals. Without the fets i have drive and no dc.

 

[Perry Babin]

On post 99, you posted an image with the FETs in the circuit. What happened between then and now?

 

[mnhiphop101]

The fets on one side blew. I found out the inductor on that side was shorted. With the inductor out the amp works fine. When I dropped in a replacement inductor it went back to not switching again. It looks like its trying to start switching when I apply signal but cant
.

 

[Perry Babin]

Did you pull the replacement inductor back out to confirm that it will again power up?

 

[mnhiphop101]

Yes. With 1 leg lifted on both inductors i get rail to rail oscillation. When I put the legs back in it oscillates normally for 1 or 2 seconds then turns into the wave in the picture.

 

[Perry Babin]

I was referring only to the replacement inductor.

Does the amp pull excessive current?

Do you see DC voltage building on the speaker output (after the relays engage)?

 

[mnhiphop101]

No it does not pull current.

No dc on speaker terminals

 

[Perry Babin]

Post a photo of the PS driver board.

 

[mnhiphop101]

If I put either one of the inductor legs it i get signal on the terminals but when I put both in I get this on the terminals.

 

[mnhiphop101]

Here ya go

 

[mnhiphop101]

I just noticed with either one of the inductors in the wave on the center leg of the fets is normal for 1 second then starts to looks like this.

 

[Perry Babin]

That looks like the low side.

Didn't you say that the amp worked normally with only the original good inductor in the board (other inductor out)?

 

[mnhiphop101]

I was. I dont know what happened

 

[mnhiphop101]

The high side looks identical to the low side

 

[Perry Babin]

But it's not the center leg. It's the source leg, correct?

Without the inductors, do you still get rail-rail oscillation as you did post #110?

Is the amp going into protect with the inductors in the circuit?