I have a behringer 2500. both channels are distorted but not out. what would need to be replaced.
It seems to me that you have a bad transistor, T14 or T13 to be precise. T14 most certainly is in short circuit or its companion T13 (T14 is a small signal NPN transistor whereas T13 is a small signal PNP transistor). I just fixed one with the same symptoms as yours. You should be able to measure T14 collector voltage against ground (metal chassis) and the reading must be very close to +15VDC. Also, measure T14 emitter voltage to ground and the reading must be very close to -15VDC. If any of those voltages is compromised, you will not be powering the amplifier's operational amplifiers (U4, U5, U6) right. Check T14 and T13 with your multimeter and replace them as needed. Also, keep in mind that after replacing any of those transistors you will be required to readjust the BIAS current for your amplifier's drivers, which by the way, is a very easy task to accomplish. You know your BIAS current is misadjusted when your output transistors get really hot even under no signal conditions or when your amplifier distorts at very low volume levels or on high frequencies amplifying. To adjust the BIAS current for channel 1's driver transistors, wait until the amplifier has cooled down, locate and adjust VR3 until you read 80 mV across R2. To adjust BIAS current for channel 2's driver transistors, locate VR6 and adjust it until you read 80mV across R106. You need to wait until the amplifier cools down to set BIAS current right, If the output transistors' heat sinks get hot before reaching proper BIAS current adjustments, wait until they cool down to average room temperature and retake BIAS current adjustment. Once both channels BIAS currents have been readjusted, apply a thin coat of thick nail polish to the sides of VR3 and VR6 to keep vibration from misadjusting BIAS currents again... T14 goes down under severe BIAS currents shifting and it just makes me wonder as to why BEHRINGER does not apply a setting substance to VR3 and VR6 so they do not shift under sever vibration conditions, after all, almost any major amplifier manufacturer in the world does it. Good luck!
9/17/2021 9:46:59 AM •
Behringer...
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Answered
on Sep 17, 2021
