Kicker ZX750.1 Makes Squealing sound when powered up

[bigpun4fubu]

Ok I finally have a DC clamp meter and it pulls 8 to 10 amps at idle with no input signal or speaker connected , removed all the output mosfets and the squealing stopped, then checked them all twice with diode check and ohm check, found three oddball ohms readings on the IRF9640 mosfets under 1 megaohm so i replaced those , and put all the rest back in and the squealing is back anyone have any ideas?

 

[bigpun4fubu]

also the 3 yellow 2200uf capacitors by the power and ground connectors are getting hot

 

[bigpun4fubu]

does anyone know why this would be doing this and pulling excessive current at idle?

 

[Perry Babin]

Does it pull excessive current if you pull the rectifiers?

Do you have a scope?

 

[bigpun4fubu]

I do have a scope, and ill pull them and check

 

[bigpun4fubu]

it pulls 1.06 amps at idle with rectifiers removed which is normal

 

[Perry Babin]

Remove the output transistors, reinstall the rectifiers, solder a jumper between legs 1 and 2 of U11. Do you see a clean square wave on the gate pads of all of the output transistors.

 

[bigpun4fubu]

this is the result on the gate pads

 

[Perry Babin]

Adjust the trigger level to see if you can get the scope to lock on the waveform. If it won't do it with DC coupling, switch to AC coupling and set the vertical amp to 2v/div.

That's the high-side FETs. Also check the low side FETs.

 

[bigpun4fubu]

here you go

 

[Perry Babin]

If you get that on all of the high and low side FETs, you may have a bad inductor.

 

[bigpun4fubu]

i get that on all fets, how do i check the inductors?

 

[Perry Babin]

With all FETs in the circuit and all semiconductors tightly clamped to the heatsink, power it up through a 15 amp fuse and monitor the current draw. If it's drawing ~10 amps of current like before, twist the output filter inductors to see if the current draw changes significantly.

Also look for individual windings that are slightly darker than the others.

Does the board show any signs of heat stress (darkened or brittle) under/around the inductors?

 

[bigpun4fubu]

ok i didnt really get much change there it did fluctuate anywhere from 4 amps to 13 amps but it did that even without twisting inductors the power fets got very warm i noticed but im sure thats just because of the excessive current draw. no darkened or brittle heat stress on board, and inductors were barely even warm when i handled them

 

[bigpun4fubu]

the current draw dropped as the frequency of the squealing increased and as it got lower or louder it increased

 

[Perry Babin]

Does twisting the power transformer make a difference?

 

[bigpun4fubu]

didnt really make a difference at all did the same without touching them

 

[Perry Babin]

Did you do any work on the power supply?

 

[bigpun4fubu]

i tried the transformer again, no difference , gets really warm

 

[bigpun4fubu]

no sir, havent messed with the fets or anything