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Old 7th September 2006, 05:55 AM   #11
vypr is offline vypr  United States
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oh and one more thing.....it looks like someone fixed this amp before i got it because i see different color caps in the filter banks, but i was wondering on this amp the MTX Thunder 2300 do you know if this amp comes with heatsink compound on the mosfets from the factory, it looks like it has a mylar or something pad insulating the mosfets from the chassis. I want to get all that white stuff off of there because it is too messy, i recently fixed a MTX Thunder 240 and it didnt have any heat sink coumpound on it just the little removable pads under the mosfets, they felt rubbery.

I was thinking since i suspect someone was working on this amp before my friend bought it and blew it up now i have to fix it again maybe those black areas around the .1 ohm resistors are from maybe when the amp failed before it was fixed the first time.
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Old 7th September 2006, 07:30 AM   #12
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The 2300s used both metallic insulators and sil-pads (rubbery pads). All of the old compound needs to be removed. If you use an insulator that's designed to be used dry, you don't have to use compound. The sil-pads are generally designed to be used dry. If you use something like Kapton or mica insulators, you'll need to use compound. Apply just enough to coat the back of the transistors. If you use mica insulators, you have to apply compound to both sides of the insulator.

To get the bulk of the grease out, use a stiff piece of cardboard or plastic. Then clean the remainder with acetone and paper towels (outside with good ventilation).

Any areas that are discolored need to be investigated. If the area under the resistors is black, you should pull them and check them individually. They're connected in parallel on the board so you can't check them reliably in the board. Where the board is discolored, you need to clean it with acetone. Then you should be able to determine if the board is damaged.

When you order parts, you should order ~10 of all of the small transistors (MPSW92, MPSA06, MPSA42, MPSA56...). I can't recall any amps where the 6523s have failed but they're likely inexpensive so you should get 5 or 10. The extra parts will be cheaper than shipping if you have to reorder.

If some of the drivers have failed, you may have to remove many of the small transistors to check them. I've seen them short, open and leak. Leaking and open transistors can be tough to find in the board.
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Old 8th September 2006, 09:14 PM   #13
vypr is offline vypr  United States
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ok thanks, ive ordered the parts i needed, when i recieve them what should i do first, pull all the bad fets of the one channel and put the fets in the power supply and try to power it up, oh and i bought a fuse holder for my power supply so i can wire a 10 amp fuse inline so i dont damage anything

Thanks,
Mike
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Old 11th September 2006, 08:58 PM   #14
vypr is offline vypr  United States
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I got the parts in today but i did not get all of them. I just got in the mpsw92s, irf3205s, and the irf540s. Im still waiting on mpsa06 mpsa56, mpsa53, mpsa42, and mps6523
So heres what i did so far i took a bank of 4 mosfet outputs out
and replaced the mpsw92s and the irf3205s and the unit powered up like normal without the 4 outputs in the left channel, it was the 4 closest to the input ok, so im like ok maybe this thing will work, so i put the irf540s in and tried it, the unit turns on but it is drawing current like crazy, keeps poppin the fuse i take them out no more current draw, so i dont know what to do could u have another bad driver somewhere, because im gonna change all the transistors on the lef channel thats why i ordered all of them, do you think those irf540s could be bad , i tried 4 more 540s and did the same thing, so i dont know i hope its those other drivers, because im having bad luck with this.
Thanks
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Old 11th September 2006, 09:25 PM   #15
vypr is offline vypr  United States
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they are mpsa93s not mpsa53s sorry for the mistype
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Old 11th September 2006, 09:32 PM   #16
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It could be a driver. If it's a shorted driver, it's relatively easy to find with your ohm meter.

It could also be that the bias current is set too high. Often when you replace the outputs, the new outputs have a lower threshold voltage. If the bias is not set lower for the new FETs, the amp will draw excessive current. Try turning the blue bias pot fully counter-clockwise. If the current draw is still excessive, it's likely that you have a defective driver.

You said you replaced 4 540s. It's best to replace all of them. Even though 4 may have survived, they were likley subjected to the same conditions that destroyed the other 4. If you don't replace them, you should at least pull them and check them for proper operation.
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Old 11th September 2006, 09:38 PM   #17
vypr is offline vypr  United States
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ok im going to swap the other 4 fets out and turn the bias pot all the way don ill let you know what happens
thanks for your help perry
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Old 11th September 2006, 10:29 PM   #18
vypr is offline vypr  United States
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ok i swapped out the other 4 540s and turned the bias pot all the way counter clockwise, i power it up and it keeps spiking the ammeter on my power supply like in pulses but takes a few secs to blow that fuse too longer than before any suggestions perry
thanks,
mike
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Old 11th September 2006, 11:02 PM   #19
vypr is offline vypr  United States
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ok i found another resistor that was burnt it is r175 i removed it and ohmed it it says it is like 3 ohms that doesn't sound right, do you know what the value of r175 would be, it is right by the left speaker positive wire in the board
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Old 12th September 2006, 12:55 AM   #20
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Is it too burrned to read the color bands?


On the images I have here, it looks like it may serve the same function as R164 on the other side of the board (across the positive and negative speaker terminals). If they are the same, maybe you can read the other one. If it is connected directly across the +/- speaker wires, it should be much higher than 3 ohms.

Did you check the other bias pot? Many times people think that those pots make the amplifier produce more power so they turn them up.

If it's not the biasing, it's likely a defective driver. If you have a lighted magnifying glass, inspect all of the components near the channel that failed. For resistors, look for darkened areas. For the small transistors, look for cracks or bulges in the case of the transistor. This isn't exactly a high-tech way of troubleshooting but sometimes it works.

If you didn't find any shorted drivers, you're going to have to look for open transistors. Most of the transistors have a pin configuration of Emitter-Base-Collector (A06, A56, W92, A42). Look up the datasheets for any others. For the NPN transistors (A06, A42), place the red lead on the center pin. You should read no more than 0.7v on diode check when you touch the black lead to the other pins of the transistor. For the PNP transistors (W92, A56), the black lead goes on the center pin. Again, you should read no more than 0.7v on diode check when you touch the other meter lead to the other pins of that transistor.
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