Parallel connection of power mosfets with two of 5 smoking
In opening this amplifier up, which was supposed to be brand new but had smoke coming out of it from the first time connected to a power source, I found on the one side of output power mosfets a group of 5 IRFZ46N devices that appear to be wired in parallel with a couple exceptions. device #s 3 & 4 in that set of 5 immediately begin burning upon application of a 12V source with a visual of the parts showing a bright red dot approximately in the center of the case area.
The wiring, as I mentioned, for all 5 is parallel connections with a 100 ohm resistor into the Gate input also all 5 paralleled with the exception of #3 devices input resistor is not connected to all the other resistor inputs and Gate pins. Thus my ohm meter reads 25 ohms across each of the 4 100 ohm resistors that are parallel connected as expected and the middle one, with no connection on the mosfet side though shorted on the other side with the other 5 reads 100 ohms.
Given the identical wiring, would anyone think that those two Mosfets that immediately start burning are just bad components which can be replaced or does anyone think the whole circuit as described is somewhat suspect having all those devices paralleled in the first place?
Further, should that middle 100 ohm resistor actually have a connection on the Mosfet side to the other 4 so that the group as a whole are connected the same? I jumpered that connection as an first try experiment which made the resistors measure only 20 ohms, what would be the case with 5 100 ohm resistors in parallel, but the result was still Fets 3 & 4 immediately started burning through their case. No short circuit protection was in evidence based on the fact that the burning continued until power was removed. Further, the amp should not have even turned on as far as I know since no signal at all was ever connected to or applied to the remote input of the amp. My other amp only works when a signal is applied to it's remote input, and I would think they all work similarly, maybe I'm wrong. Any suggestions? Anyone have a decent schematic?
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Re: parallel connection of power mosfets with two of 5...
The IRFZ46N are n channel high speed switches . They basicly drive the Mosfets. Sounds like you have some problem there my friend, and unless you paid alot for this amp. Its going to need probobly all the n channel switches as well as every mosfet + the bias resistors repalced. Before plugging in the amp jump out the fuse with a 100 watt light bulb.. If the bulb glows brightly when you apply power there is still a short in the unit and could be in the switching power supply section of the amp. If it glows bright and dims, The shorts are most likly gone. The bulb will minimize the amount of current the unit can draw and most of the time wont let the new parts blow out. Check out this service number and see if they can help you. Good Luck Main support number 978-823-0300
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Well it seems to me that the pictures of this amp show green ATC fuses which would be 30 amp fuses. What is your inline fuse from the battery? 40 amp fuses for the amp is too much current for the amps powersupply. If there was a short in the powersupply the max ammount of current that it could draw would be larger than designed to handle therefore damaging the amp.
Open the sub box and see what it looks like before you go purchasing stuff with no problem for certain. You may have had wires touch and they will smoke. Also try connecting a different speaker to the amp and see if it works. this lets you know if the amp/speaker is working or not
depending on how good you are with electronics and soldering,you may be able to.i used to do warranty repair for rockford and they use mosfet semiconductors in the power supply.it is probably repairable cheaper than a new one,but by someone that knows how to do it.
First of all is the mosfet your talking about in the output section or in the power supply section? Most car amps use mosfets in the power supply section, some use them in the output section. To test the transistors in your amp, take a digital volt meter and set it to diode check. Then take the leads and put them accross the first and third legs of the transistors. Usally the red test lead on the first leg and black test lead on the third leg of transistor. If you get a reading of 000 then transistor is shorted. If you get a reading below 600 then transistor is on it's way out if not allready or it's next to a shorted transistor that is it's complimentry output transistor. comonly you will have 2 transistors working together, one NPN and one PNP per a channel, or 4 of them in a bridged type output circuit depending on the watts and how man channels your amp has. I was just looking at the specs of this amp and it's got me confused. It says it's a 2 channel but looking at all the info on different pages it says at 4ohm:200wattsx4 and at 2ohms:300wattsx4 and 1 channel mono 600watts into 4ohms. weird for a 2 channel. anyway that is how you test your transistors. Same way for the power supply section but, you will come accross a couple or more switching diodes that look like transistors and you will get a 000 reading when you test those like I specified. They rarely go out and most of the time there is only 2 of them. They will have a diagram like a diode on the front showing you which way the power flows. Let me know what you find out. Your amp should have went to protect mode if you smoked a mosfet.
Broken legs on the rectifiers or an intermittently shorted common mode inductor would be the likely suspects. The common-mode inductor is just to the right of the capacitors in the photo. Install a single 15 amp fuse in ONE of the 4 fuse holders (other 3 fuse holders empty) and power up the amp. Twist the inductor to see if the amp draws excessive current (which would blow the fuse) or to see if it sparks.
these are the trasistors..The ones closest to the power connectors are probably the ones for power supply and or 15 volt regulators..The rest are for amplifier section.Im guessing all except regulatos will be MOSFET transistors .If you are to replace them ..Stick to original parts..You can probably find these at mcmelectronics.com or mouserelectronics.com Just give then the numbers on transistors .Also make sure all other parts around shorted parts are okay before you install new parts..