OK, while waiting for my mtx 6500D parts to come in I decided to get back to the kicker zx750.1 in working on. So I replaced both input and output MOSFETs on the board(all 8 irf3205s), all irf640 and irf9640s because a couple were shorted, and my gate driver transistors were fried. I saw someone else's post where they replaced the input 47ohm gate resistors to 100 ohm because they stated the circuit allows enough dead time to use 100 ohm resistors. So after bench testing and confirming it works great now, I hook it up in my car for the real test and it Buzz's real bad, no problem because it still plays great and I read another article stating the sink needs the proper grounding to get rid of the noise. Now its working great pushing my 8" Rockford p2d4 wired down to a 2 ohm load with the gain barely turned a quarter of the way up, when it cuts off due to overheating. The only side that got really hot was my rail of input output MOSFETs. Should I have left the input gate resistors stock or do I need to do some more research when I get home? Attached are pics of the burnt gate transistors and burnt MOSFETs b4 replacement. Thanks
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Could you determine if the 47 ohm gate resistors were factory and in fact 47 ohms? The correct value for the gate resistors is 100 ohm.
Assuming you replaced all 8 mosfets w/ IRF3205 (preferable batched matched and not conterfiet or bogus parts) and KTA1504GR drivers and of course 100 ohm gate resistors and based on your comments the power supply may not be the issue. Unless the grounding issue you refered to may have caused one or two mosfets to become weak. When I firsted stated seeing this amp come back for repair this was a common problem-the plastic stand off would not allow a good connection to the chassis and would cause the amp to blow out on the test station.
The shorted outputs may have been a result of the output inductor/s. The rubber sleeves on the input and output leads become perforated and intermittantly short to the inductor windings and should be replaced. Whenever this amp comes back for repair to Kicker's electronic repair department, regardless of the issue we replace the sleeve with braided or woven fabric tubing.
The amp cutting out at 1/4 volume may be due to the preamp board biting into C169 10uf/200v SSP across the spkr terminals. Check for any knicks or tears in the capacitors outer coat and use cardboard to insulate.
If I can help in any way please let me know. The cutting out issue can be a real bear. Also, you may want to move your post to the Car Audio sub forum where you will find a wealth of good information and help!
Assuming you replaced all 8 mosfets w/ IRF3205 (preferable batched matched and not conterfiet or bogus parts) and KTA1504GR drivers and of course 100 ohm gate resistors and based on your comments the power supply may not be the issue. Unless the grounding issue you refered to may have caused one or two mosfets to become weak. When I firsted stated seeing this amp come back for repair this was a common problem-the plastic stand off would not allow a good connection to the chassis and would cause the amp to blow out on the test station.
The shorted outputs may have been a result of the output inductor/s. The rubber sleeves on the input and output leads become perforated and intermittantly short to the inductor windings and should be replaced. Whenever this amp comes back for repair to Kicker's electronic repair department, regardless of the issue we replace the sleeve with braided or woven fabric tubing.
The amp cutting out at 1/4 volume may be due to the preamp board biting into C169 10uf/200v SSP across the spkr terminals. Check for any knicks or tears in the capacitors outer coat and use cardboard to insulate.
If I can help in any way please let me know. The cutting out issue can be a real bear. Also, you may want to move your post to the Car Audio sub forum where you will find a wealth of good information and help!
Finally got some time check everything out again. Yes they were 100 ohm, not 47 ohm resistors. I was taking a reading on the board and I'm guessing the shorted transistor was giving me a false reading.
Now that you mentioned it, I did have to replace 4 of the IRF3205s after doing a bench test. I was testing the buzzing issue, which was definitely from the improper grounding of the sink, in and out of the sink. It would only buzz in the sink. And yes all parts are from digikey from same batch.
I didn't see any knicks or tears by c169, but did notice C08 is looking a little puffy on top. I'll replace all four in this group to b sure.
How do I move this thread?
Thanks for the helpful reply. Will get back after replacing those caps.
Now that you mentioned it, I did have to replace 4 of the IRF3205s after doing a bench test. I was testing the buzzing issue, which was definitely from the improper grounding of the sink, in and out of the sink. It would only buzz in the sink. And yes all parts are from digikey from same batch.
I didn't see any knicks or tears by c169, but did notice C08 is looking a little puffy on top. I'll replace all four in this group to b sure.
How do I move this thread?
Thanks for the helpful reply. Will get back after replacing those caps.
When I designed a irs2092 based class d amp I used 10R gate resistors as the mosfets were high power ones and so had a high capacitance gate.
I suspect your 100R resistors are causing the mosfets to switch on and off too slowly putting the mosfet into its linear region and so soaking up lots of power and over heating.
Also check dead time is not too small and causing cross conduction.
I suspect your 100R resistors are causing the mosfets to switch on and off too slowly putting the mosfet into its linear region and so soaking up lots of power and over heating.
Also check dead time is not too small and causing cross conduction.
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