I am trying to fix an audiobahn a2300hcx amplifier that had burned out a couple of years back. The amp had pop spilled on it and it went through one of the fans and nothing seemed to happen at that time. The next morning the amp was fired up and it blew out and the protection turned on. I opened up the amp and noticed that three of the mosfets were definitely blown up so I replaced them with new IRFZ44n. There was some blackening on the resistors (gate?) right in front of them so I tested them to check their resistance and they tested out at the proper level. So I reassembled the amplifier and hooked it up to a battery to see if it would function properly and it blew two of the same fets again. One of the fets that I replaced appears to still be in good condition. I removed the two damaged fets and powered the amp up again. The fans and everything turn on but the protection circuit is still on. Can someone please tell me what would cause just these two mosfets to keep blowing up.
Alright, I will try replacing all of the fets on the bad channel and test the outputs. Then I will replace all of the outputs on that channel. I will also be replacing the resistors for each mosfet and output. I will have to wait a little while before I can actually replace these components because I will have to order some more mosfets and some outputs. Thanks for your help and I will post how everything turns out after I do the repairs.
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.
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?
http://pdf1.alldatasheet.com/datasheet-pdf/view/51677/FAIRCHILD/FFPF10U20DN.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.
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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