blowing output transistor DD Z2

[yoppi]

Hello

I'm repairing a DD Z2. It came with the power supply and output burned.

I have repaired the power supply (all the new transistors, gate transistors, gate resistors and it works normally) I get + 175v and -175v.
In output, I changed all the irfp360LC, resistances 33 ohm and 100kohm.
I have repaired the output control card, changing the 4 irs21844, I have reviewed capacitors, resistors and diodes.

the amplifier has been running normally, but the last time I turned it on, 6 IRFP360LC has exploded.
the other irfp360lc seem to be fine ....

What could have happened to him? It does not make sense that it worked well all afternoon ...

 

[Achim1409]

I had it, That the big resistors in Front of the driver Board was out of tollerance. Should be 2 ohm i think.

 

[yoppi]

I have checked and are within tolerance. 2,2ohm

 

[Perry Babin]

Is it possible that you have an intermittent via on the driver board?

 

[yoppi]

I checked it completely and I have not seen anything wrong in drive board......

 

[Perry Babin]

The vias would be in the main board. They are the copper 'barrels' that connect one side of the board to the other and in this instance, where the pins of the driver board go into the main board. They are often damaged when the driver board is removed.

 

[yoppi]

I have reviewed all the clues and this is all correct. I have replaced the exploited transistors and 4 IRS21844
It has been working correctly for a couple of hours. I turned off and on again and exploded again 6 transistors .....

 

[MAAC0]

Yoppi. Check if You have fake transistors. Where did You get them ?

 

[Perry Babin]

When you switch it on, do you get rail-rail oscillation as soon as the rail voltage comes up or is there a slight delay?

 

[yoppi]

Yoppi. Check if You have fake transistors. Where did You get them ?

They are purchased in Mouser. they are original. all materials, irfp360lc, 21844, resistances, etc ...

 

[yoppi]

When you switch it on, do you get rail-rail oscillation as soon as the rail voltage comes up or is there a slight delay?

I'm going to check that with oscilloscope. the gate transistor pulse on power supply is correct.

 

[yoppi]

Is it possible that the 30 amp power supply I have in the workbench is too small for the start of the amplifier?

 

[Perry Babin]

What type of 12v supply is it?

 

[yoppi]

My 12v power supply is diamond gsv-3000 30 amp.

I have noticed that the resistances that I indicate in the attached image, are out of value, should be 10kohm and are very out of value ...
What function do those 4 resistors have?

 

[Perry Babin]

Are the resistors connected across the rail caps?

I'm not familiar with that supply. How were you powering the amp during previous testing?

Has it had trouble powering other amps?

 

[yoppi]

Yes, I think the resistors are connected across the rail caps...

They have started to smoke. As you can see, 2 of them are discolored.

What do you mean when you say that you had the source connected?

No, that source is the one I use regularly and has never given me problems.

 

[MarioRestucci]

If this is an unregulated power supply, when you not have any output fet installed and try to power up the amp, the rail voltages rise up much higher than normal (generally higher than the rail caps voltage value) and rail voltages pulldown resistors start to smoke.

 

[Perry Babin]

Did the value of the resistors go up or go down?

 

[yoppi]

If this is an unregulated power supply, when you not have any output fet installed and try to power up the amp, the rail voltages rise up much higher than normal (generally higher than the rail caps voltage value) and rail voltages pulldown resistors start to smoke.

What power supply do you recommend to use? diamond regulate voltage but not amperage

 

[yoppi]

Did the value of the resistors go up or go down?

the resistances lowered their value, between 5 and 8 kohm