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-   -   Blown IRFZ44N (https://www.diyaudio.com/forums/car-audio/78522-blown-irfz44n.html)

cruck00 28th April 2006 09:06 PM

I have tested the output pnp's (TIP35C) and the mosfets now. Here's how the pnp's measured on the bad side from farthest to closest to the mosfets: pnp's 1,2,4,5,6 all read 4.7 ohms from legs 1-2 and .2 ohms from legs 2-3. The #3 pnp's readings were .2 ohms for legs 1-2 and 0 ohms from 2-3. 7 measured 5.28 M Ohms 1-2 and legs 2-3 just kept going up. # 8-12 all read 5.28 M Ohms 1-2 and the measurement kept jumping around so I never got an exact reading(I am counting the legs from left to right while looking at the front of pnp). The mosfets(IRFZ44N) read (starting from the end of the pnp's): 1,2,3,4,5, legs 1-2 422 Ohms, 2-3 96 Ohms. #6 which had been replaced when the other two (7,8) that blew measured 1 Ohm for 1-2 and 96 Ohms for 2-3. 7 and 8 measured 243 Ohms for 1-2 and 0 Ohms for 2-3 without mosfets in the positions. 9 and 10 measured 0 Ohms for 1-2 and 96 Ohms for 2-3. I can honestly say I don't really know waht to make of this for sure and any help would be greatly appreciated. Otherwise I am just going to replace all of the pnp's, mosfets, and resistors that are just off of the mosfets.

cruck00 28th April 2006 09:07 PM

I also have the measurements from the good side of the board. That side is using TIP36C pnp's instead of TIP35C pnp's though.

cruck00 28th April 2006 09:20 PM

Sorry my reference to the TIP35C's being pnp's was wrong, they are actually npn's.

TO-3 30th April 2006 02:06 PM

Quote:

Originally posted by cruck00
I have tested the output pnp's (TIP35C) and the mosfets now. Here's how the pnp's measured on the bad side from farthest to closest to the mosfets: pnp's 1,2,4,5,6 all read 4.7 ohms from legs 1-2 and .2 ohms from legs 2-3. The #3 pnp's readings were .2 ohms for legs 1-2 and 0 ohms from 2-3. 7 measured 5.28 M Ohms 1-2 and legs 2-3 just kept going up. # 8-12 all read 5.28 M Ohms 1-2 and the measurement kept jumping around so I never got an exact reading(I am counting the legs from left to right while looking at the front of pnp). The mosfets(IRFZ44N) read (starting from the end of the pnp's): 1,2,3,4,5, legs 1-2 422 Ohms, 2-3 96 Ohms. #6 which had been replaced when the other two (7,8) that blew measured 1 Ohm for 1-2 and 96 Ohms for 2-3. 7 and 8 measured 243 Ohms for 1-2 and 0 Ohms for 2-3 without mosfets in the positions. 9 and 10 measured 0 Ohms for 1-2 and 96 Ohms for 2-3. I can honestly say I don't really know waht to make of this for sure and any help would be greatly appreciated. Otherwise I am just going to replace all of the pnp's, mosfets, and resistors that are just off of the mosfets.
You'll want to replace any of the components that are shorted like your first bank of 1-6. As for the mosfets, remove the shorted bank from the board and measure the pads where the devices were.

cruck00 30th April 2006 09:54 PM

Is it going to be necessary to replace the two transistors that are in between the mosfets and the npn's?

cruck00 1st May 2006 05:00 PM

I have been able to identify the part numbers of these transistors but have not been able to find a decent supplier for them yet.

TO-3 1st May 2006 05:56 PM

Quote:

Originally posted by cruck00
Is it going to be necessary to replace the two transistors that are in between the mosfets and the npn's?
Those should be 7815s and 7915s. The two-legged ones are high power diodes. You should not need to replace them.

Quote:

Originally posted by cruck00
I have been able to identify the part numbers of these transistors but have not been able to find a decent supplier for them yet.

This place has just about everything you need.

DIGIKEY

cruck00 1st May 2006 06:25 PM

I can't remember for sure but I think they were three legged and looked exactly like a transistor without the metal backing on them. I have ordered all the mosfets, npn's, and resistors that I think I need, just not these two parts. What kind of readings should I expect when testing the pads after I remove the mosfets and npn's?

cruck00 2nd May 2006 12:38 PM

The part number on the two components is F10U20DN.

Perry Babin 2nd May 2006 01:37 PM

http://pdf1.alldatasheet.com/datashe...PF10U20DN.html

If these are the components you have, you will check them like a normal diode. Look at the datasheet to see the orientation of the diodes.

After replacing the components, you should use a series connected current limiter in the power wire. A 1.5-2 ohm 25w-50w (watt) resistor will work for most amps. You can also use a car headlamp. Use a dual beam type with the large reflector housing. Connect the filaments in parallel. Mount the amp back in the heatsink (transistors clamped) before applying power. This will help protect the new transistors if there is another problem.

With the components removed, you should see no low resistance readings between pins 1 and 2. You may see a relatively low resistance between pins 1 and 3 but it should not be a direct short.


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