Hifonics XX-Zeus has not the full power

[tobi320i]

hi,i am Tobi from Germany.Advance,sorry for my bad Englisch .

i bought a defect Hifonics XX-Zeus class d mono Amp (1600 watts RMS) and repaired it.
in the output stage part 3 transistors had a short circuit.(Two IRF640N and one IRF9640).
the consequence was a blown power supply (eight IRFP064N plus the drivers 2SA1275)

a final test shows that the amp does not bring the full power.you can hear clipping
very early and the amperage to the amp is only 12 ampere at 4 ohm load in the
moment when the clipping begins.

so i made a test.the voltage from the amp-power supply is about +- 60 volts(so 120 volts)
at 12 volts input.
i connected a 1,4kw heater to the 120 volts.they remained nearly constant and the amperage to the amp was about 138 ampere.so i think the amp power supply is ok.

in the link below you can see a video where you can hear the clipping noise inside the amp,but without a connected speaker.input signal is 30 hz.
I increase the volume level until the clipping,then you can hear it.it comes from the four blue
capacitors.

in the other link you can see and hear with connected speaker.

why does this amp have not the full power?

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[Perry Babin]

Confirm that you have a good drive signal on every individual gate leg of the output transistors. It should drive approximately 10v from the rail.

 

[tobi320i]

hi perry,thanks for the answer.
please lock at the attached pictures.
the GND of the oscilloscope,i connected with the minus of the external power supply.is that correct or do i need another GND-point
for this measurement?or can i measure with an multimeter too?on AC or DC?
on every gate-leg is a signal

 

[Perry Babin]

Does the amp clip at the full rail voltage with no load?

Does the output clip symmetrically top and bottom when it clips?

 

[tobi320i]

the rail voltage stays constant when the amp is clipping with no load.
127,4 volts without an input signal,127,6 volts with high input signal when the amp clips.

i think it clips symmetrically yes.the picture shows the output with no load

 

[Perry Babin]

Does the rail-rail square wave on the outputs and on the input of the output filter inductor remain the same amplitude (swinging ±60v) when the output clips?

 

[tobi320i]

I do not know exactly what you mean.
what points should I measure? point 1 and ?
see picture

 

[Perry Babin]

You can check on the drains of the FETs or where the drains connect to the larger inductors.

 

[tobi320i]

ok.yes,the amplitude is the same when the output clips

 

[Perry Babin]

Does the audio clip early at points 3, 4 or 5 (in your photo)?

 

[tobi320i]

no it don´t.
do you have a guess?

 

[Perry Babin]

The only things between point 5 and the speaker terminal are the relay and the wire.

 

[tobi320i]

do you have a schematic for this or another amp which works with the
IRF640N and the IRF9640?

 

[Perry Babin]

I don't have one that uses this drive circuit.

Do you need a schematic? If there is no drop in signal on the inductors and it doesn't clip at a low level on the inductors, the problem has to be beyond the inductors.

 

[Perry Babin]

This one may be close enough but doesn't show the driver circuit.

 

[tobi320i]

thank you.
i dont know what i should do now.you told something from the gate voltage (10 volts)
in my case there are only 8 volts.you can see it on the pictures previously sent.

 

[Perry Babin]

8v is good enough.

If the output before the relay doesn't collapse under load, the problem is beyond the inductors.

 

[tobi320i]

now i have looked at the gate signal again.on the peaks the input signal can be seen(now 100 hz)here you can see the clipping too.

driverboard defect?
do you have a schematic of driverboard?

 

[Perry Babin]

I don't understand.

Is the signal before the relay collapsing under load or is it capable of swinging ±60v with a load?

 

[tobi320i]

it is not collapsing under load.it does not matter if the load is
affiliated or not.
it is swinging ±60v