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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?
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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If it still works leave it alone and use it as it is. Smoke usually comes from the emitter resistors of the power transistors if they're pushed too hard. Those resistors are about the only electronic devices that still work after you let the magic smoke out.
it could be a parallel wire, connecting the smoke detectors to each other so that if one goes off they all go off, do the other smoke detectors have the same wire ?
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
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.
If it begins to smoke with only the B+, ground and remote connected, the power supply transistors have likely failed.
The protection light generally won't come on if the power supply is blown because the supply must be working for the protection circuit (which protects the output transistors) to engage.
The power light may be connected to the B+ side of the power supply. If that's the case, the power light will illuminate even if the amp is inoperative.
I have never heard of this brand of amplifier.. but NEVER hook up unequal ohm loads to a amplifier. the only way i could think to do it would be to hook up 1 of each sub on each side... what way you are spreading out the ohm load equally on both sides
but again if you dont do your math and you run too low of a ohm load you WILL smoke that amp..
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