Digital Designs Z2HV

[Perry Babin]

Post the gate pad waveform for the FET location that's loaded.

 

[caraudioguy2100]

Scope set to 5us 5volts/div

 

[Perry Babin]

I don't see a problem if all locations look like that.

Could you have had a solder bridge on one of the FETs?

 

[caraudioguy2100]

I will clean the board again but don’t think so .

Could it be bad fets ?

 

[caraudioguy2100]

Reinstalled 3 fets out of 6 here is what I get on the gate legs for the fets 2 of them get hit within 10 seconds

Scope set to 5us 5 volts Div

 

[Perry Babin]

Measure the resistance from the gate pad of each FET to the emitter of the driver transistors that are driving them.

 

[caraudioguy2100]

I get 47 ohms from gate pad to emitter

 

[Perry Babin]

Swap the FETs between this bank and another to see if the problem follows the FETs.

 

[caraudioguy2100]

I see a problem with that bank of fets .

I pushed on a couple of the drivers with my finger then checked for drive signal on the gate pads .

i have no drive signal to the gate pads of 3 fets I also do not get drive signal to the drivers I’m missing drive signal on the emitter of the pnp and npn drivers that control 3 fets in that bank

 

[caraudioguy2100]

Ok fixed the issue there now I will try swapping fets to see if the problem follows

 

[caraudioguy2100]

I replaced the fets and the problem is still there just the one bank of fets gets hot .

So the fets are not the issue it’s something else that controls that bank of fets

 

[Perry Babin]

If all 3 of those waveforms were driven by the same NPN driver transistor, it would seem that there is a problem between the emitter of the driver and the gate pads. That would leave traces and gate resistors.

 

[caraudioguy2100]

I will check the traces and gate resistors to see if I can locate the problem

 

[caraudioguy2100]

All traces are intact also all gate resistors are new and measure fine .

Could I possibly have a bad transformer ?

 

[caraudioguy2100]

I reflowed the solder and loaded to spots with caps here is what I get on the gate pads for the fets . Scope set to 5us 5volts div

 

[Perry Babin]

That looks OK.

When you checked the FETs, did you confirm that the FETs read OL from the gate to the other two terminals?

 

[caraudioguy2100]

I checked all 6 fets here is what I get

1-2:OL
1-3:OL
2-3:3.99Mohm

probes reversed
1-2:OL
1-3:OL
2-3:OL

 

[caraudioguy2100]

I have another question as well the original drivers were A1275 and C3228 I replaced them with A1013 and C2383 they work in 5 out of 6 banks but I have an issue with the last bank of fets . Would these drivers cause issues or should they work if they work in the other 5 banks . Just asking covering all the basics before I trouble shoot more since the drive signal looks fine with loading caps but as soon as I put fets in then the problem appears

 

[Perry Babin]

In post #65, what are the circuit board designations of the 3 FETs for the 3 waveforms?

 

[caraudioguy2100]

Q9,Q9B,Q12