Subwoofer Klipsch RW-12 No audio

[falcontech]

good morning
Today I find myself repairing this sub of which I have no audio output, the speaker is working, the amplification part is composed of three boards (as in the photo), power supply board, linear board and feature board, the sub turns on but I have no audio output, I have also attached the service manual, at the moment the only thing I noticed is that LM7815CT and LM7915CT heat up a lot and I don't know if it's normal, the capacitors at first glance all seem ok, I'm waiting someone tell me where to start testing (I state that I do not have an oscilloscope) thanks

[falcontech]

Re: Subwoofer Klipsh Rw-12 No audio

all tensions are ok, +/- 25 +/- 15

[CapLeaker]

Re: Subwoofer Klipsch RW-12 No audio

The subwoofer should turn itself on when a signal is present on the input. Without a oscilloscope and audio generator makes it hard to trace the audio along the circuits and inject audio at certain points. This thing has a lot going on inside. You have to figure out if something at the input stage is blown, the feature stage or the output stage.

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

The subwoofer should turn itself on when a signal is present on the input. Without a oscilloscope and audio generator makes it hard to trace the audio along the circuits and inject audio at certain points. This thing has a lot going on inside. You have to figure out if something at the input stage is blown, the feature stage or the output stage.

not having an oscilloscope I try to do this with an amplified speaker and two test leads, I suppose the main suspects are the operational amplifiers or am I wrong?

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

yesterday I had already started to do this test, the input audio stopped on an operational amplifier (the one highlighted in the photo), after I had nothing left, later I will deepen the thing

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

I did some tests, on the photos I posted there is a bit of a summary of what I perceived with the amplified speaker. the only signal I have is on the first op amp (very distorted) then it ends up on pin number 4 of the connector with a very dark and low sound. the same signal reaches the speaker connector but I repeat it is a very low and dark sound

[CapLeaker]

Re: Subwoofer Klipsch RW-12 No audio

not having an oscilloscope I try to do this with an amplified speaker and two test leads, I suppose the main suspects are the operational amplifiers or am I wrong?

Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.

All right I will try to do these tests and I will keep you updated

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.

in the photo I reported, the outputs that could have anomalies, the other opamps do not report anything at the output

[CapLeaker]

Re: Subwoofer Klipsch RW-12 No audio

check U100

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

check U100

I checked all the outputs are at 0

[falcontech]

Re: Subwoofer Klipsch RW-12 No audio

check U100

what do i replace suspicious opamps?