Need to know if i can replace a 22 ohm /10% (1.5w ((I think due to size)) resistor with a 22 ohm / 2% 2watt.

The resistor placement is R2 in a Behringer B215D powered PA speaker. The resistor that was in it is smaller round than the replacement piece,but is the same length. The schematic does not state the wattage of the resistor so I'm a little confused. Any help would be greatly appreciated.  

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-max-2 years ago

There should not be any issue with replacing that resistor with one of tighter tolerance. and higher power rating. Considering that the replacement began to glow cherry red, there is obviously a short circuit somewhere that is passing an excessive current through that resistor. It could be what caused the previous one to fail.

Are you certain you did not goof up the value of the replacement resistor (I know I often get the 4.7k resistors and .47K resistors mixed up as well as the .47K and 0.047K or 47 ohm resistors.) Do you have an idea as to what the resistor's purpose is for? Did it look like a previous mod someone did or does it seem like it was specifically designed in and is OEM? My guess is that it is being used to retrofit a low impedance speaker onto a amplifier that is supposed to have a much higher impedance load connected it is was originally a mod, but if you are sure that you know which one resistor it is based on a schematic, then I suppose this guess is wrong. Can you upload a schematic? If it is a pull up or pull down resistor, then check follow down the node and trace to what device it is pulling up or down and start there. (The other side of the resistor in this case will be connected to Vcc, Vdd or ground.)

Also go ahead and pull out any semiconductor switches like MOSFETs and test them to see if they operate as expected. It is easy for MOSFETs to get killed and fail with an internal short. (particularly when the failure results from ESD on the gate without adequate ESD protection. I got to know this effect up close and personal when I was building flyback transformer drivers!)

hal.jensen.9 (author) 3 years ago

So I put it in and put the amplifier back together and turned it on it works but the resistor is turning red in the middle so I shut it off. The speakers are only 4yrs old 550 watt class D power. the schematics can be found by googling "wiring schematic for Behringer B215D. The resistor placement is in R4 (not R2) as stated before, I will take it back apart ASAP and take a couple of pictures and try and post them. I live in Reno NV if anyone is near to me I would be willing to pay someone to do the repairs. Text me @775-815-2758 and I'll call you ASAP. Thanks again for the replies

Which means the resistor (R4, not R2) failed in the first place because of another problem upstream (or downstream) of the component. The failed resistor is simply a symptom, and the failure of the replacement is a visceral confirmation of that.

If it "turned red" then you have a substantial over-current issue.

Would it be possible for you to post the schematic for review? I tried to find a schematic that has legible entries, but everything I found is scanned at too low resolution to identify the resistor in question or its associated circuitry.

If you can't post a legible schematic, then I'd recommend finding a shop in or near Reno to perform the necessary diagnostics and repair.

BTW, kill your last message. DO NOT post private phone numbers. It's a sure way to getspammed incessantly by the unscrupulous.

Yhea, Resistors Aren't know for their Light Emitting Properties XD I have never seen a resistor Glow Red (That I haven't deliberatly caused) Like we both said You have a major issue here. If you can send a PM to Iceng He may be able to see it with his own eyes, rater then txt and pictures. Would be your best bet to figure out what's wrong.

Sorry for volunteering you there Iceng; Be sure he at least brings you a case of beer!

And HUGE +1 to Steve on deleting you phone number !!! Stick with Private Messages

Try and Ping ICeng on this forum. He lives in Reno too.

Wired_Mist3 years ago

No problem at all.

Provided the resistance is the same, the 2% means it is manufactured to 2% tolerance. so the 22-Ohm resistor can be off by UP TO 0.44-Ohm ( or 2.2-Ohm for a 10%)

The higher the wattage, the more current it can handle. The extra 1/2W will help keep it a bit cooler. Really it won't make a difference; just don't use a lower wattage then what you pulled out.

Hope this helps; good luck !

BTW, If it was designed decently, resistors are some of the least likely components to fail. Can you send a Pic? could be more happening here.

rickharris3 years ago

Yes

kelseymh3 years ago

What seandogue said. The "wattage of the resistor" specifies the _maximum_ power it can dissipate before it overheats. Since 2W is greater than 1.5W, the new resistor can certainly handle the power load of the circuit.

Similarly the percentage specifies how close you can expect the resistor to be to the written value. Ten percent means that your "22 ohm" resistor could be as high as 24.2 ohm or as low as 19.8 ohm. Your 2% replacement will be much closer to the nominal value (between 21.56 and 22.44 ohm).

Note that this is not strictly accurate, because of the way resistors are classified after manufacture. See the Wikipedia discussion under resistors: 8.1 Preferred values

The only problem with my assumption, as I see it, is if they used hand picked 10% resistors, and or used the 1.5W rating as some sort of "intrinsic" over-current protection, which I've seen on some occasions with older electronics. the tolerance simply guarantee that when a batch of the same resistors is purchased, they will all be within N% of the target value. A tech or engineer can always weed through and pick/choose values to a much tighter tolerance. I've done so many times in a pinch (for instance, old opamp based diff-in and filter designs from the early/,mid 1980s, when the uA741 was still considered a workhorse) requiring four matched resistors for instance) , and the same goes from "intrinsic" over-current protection, although I wouldn't, even though I've seen plenty others do so.

seandogue3 years ago

I'd really have to see and analyze the circuit to be sure, but it sounds like there should be no problem overall, since your candidate replacement has a tighter tolerance (2% vs 10%) and a higher load rating (2 vs1.5W)