audio pipe 1500

[timwebb]

ok i got this amp the neg side of the out put keeps shorting out. i checked the resistors they are good

 

[Perry Babin]

Can you post a photo showing a larger area of the board?

Do you mean that the output transistors connected to the negative rail fail repeatedly?

 

[timwebb]

yes.they keep failing.

 

[Perry Babin]

That looks like a version of the massive/SinusLive amps.

Remove all of the outputs and short the positive and negative speaker terminals together.

What is the DC voltage for the high and low side FETs when you place the black probe on leg 3 and the red probe on leg 1?

 

[timwebb]

5volts

 

[Perry Babin]

That's about what I'd expect.

Are all of the gate resistors within tolerance?

Are there any traces that could open intermittently?

Does the same FET on the low side blow every time or do they fail randomly?

Do ALL of the low side FETs fail (checked out of the board) EVERY time they fail?

 

[timwebb]

Are all of the gate resistors within tolerance? yes.
Are there any traces that could open intermittently? no

Does the same FET on the low side blow every time or do they fail randomly? theyblow everytime.

Do ALL of the low side FETs fail (checked out of the board) EVERY time they fail? yes.

 

[Perry Babin]

It's odd that ALL 4 of the FETs fail at once. This would tend to indicate that the drive voltage is spiking.

Is the center leg of these 4 FETs directly connected (~0 ohms) to the output filter inductor?

 

[timwebb]

no im getting a very high ohm reading

 

[Perry Babin]

Check the other 4 FETs (center leg to inductor).

 

[timwebb]

i read 0 ohms on them.

 

[Perry Babin]

The ones with their center legs connected to the inductor are the low side FETs. That would mean that the high side keep failing.

Is there a diode on the board that has its striped end connected to the gate leg of an output transistor and the other end connected to the source leg of an output transistor (probably the same transistor that has the striped end connected to its gate)?

Do they fail with the amp idling or do they only fail when the amp is driven hard into a speaker load?

 

[timwebb]

they fail while idling.

 

[Perry Babin]

Is there a diode on the board that has its striped end connected to the gate leg of an output transistor and the other end connected to the source leg of an output transistor (probably the same transistor that has the striped end connected to its gate)?

 

[timwebb]

yes its one.

 

[Perry Babin]

If you still have a set of 4 that failed together, see if the gate is shorted to the other 2 legs on all 4 transistors.

 

[timwebb]

im going to sit this to the side till the parts get here. i read 10ohms on the output transistor gate. is this correct?

 

[Perry Babin]

Precisely where were the probes when you read 10 ohms?

If this was on the outputs you removed, did all 4 read the same?

 

[timwebb]

thats the ohms of the gate resistors for the out put.

 

[timwebb]

first one high side second low side