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Post by tibimakai on May 12, 2022 10:19:47 GMT -5
I have picked up this sub that did not work.
Found the "wire" from the coil to the speaker cone did not conduct. Measure with Ohm meter and it was open.
Replaced that "wire" and it is working now, but when it turns on it pops. Otherwise it works great.
I'm not sure what this could be, just a bad capacitor, or something bad in the amp area, since the speaker wire had an open circuit?
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Post by tibimakai on May 16, 2022 11:01:20 GMT -5
It also pops a bit when turning it off as well.
I have tested some of the capacitors, and even replaced a pair by the "hot" resistor, but there is still no change.
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Post by mastertech on May 16, 2022 13:24:11 GMT -5
Without a schematic it is hard to point to a specific component or location, but popping is usually caused by a slight amount of DC voltage on the speaker line during startup and/or shutdown. Meaning, the + and - lines may not be powering up equally and when the point arrives for the amp section to start running, there is a little dc offset. In a regular receiver, this is one of the reasons for a delay in the speaker relays activation. So in your case, if there is no DC on the speaker line when fully running, I would be looking in the power supply area first and most likely the + and - rails for the amp. Bad cap, leaky diode, possibly even leaky transistor. I would recap the power supply anyways unless it had good quality caps to begin with and even then test them at the very least.
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Post by tibimakai on May 16, 2022 14:04:53 GMT -5
I have measured the DC output, with the gain adjusted to the minimum and I have measured 3.3mV.
I'm wondering what could have damaged, since the speaker tinsel wire was damaged(with an ohm meter I was measuring in the megaohm range).
I'm thinking that something in the amp section, no?
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Post by mastertech on May 16, 2022 14:29:30 GMT -5
The speaker damage could of been from the same thing causing the popping and may happen again until you fix the problem.
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Post by tibimakai on May 17, 2022 3:14:01 GMT -5
That is possible, you are right. Here are some pictures.    |
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Post by tibimakai on May 17, 2022 3:14:47 GMT -5
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Post by tibimakai on May 17, 2022 3:20:45 GMT -5
That silicon, does not look like it is conductive yet.
Everything looks fairly new and in good condition.
I have removed one of those big capacitors(one of 4), also one of the 15V capacitors(next to the big one), the capacitor from the pwm ic(behind the heatsink) and they all have 0 or very close to it esr value.
All these from picture #5.
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Post by mastertech on May 17, 2022 13:07:16 GMT -5
You know, you may want to try another speaker just to be sure it was not damaged more then the wire you repaired. It may be internally damaged in the coil.
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Post by tibimakai on May 18, 2022 10:16:48 GMT -5
I was thinking about that also. I don't have the exact same speaker, but I have an older Klipsch 12" sub, that also needs to be repaired.
I will try that as well. Thanks
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Post by tibimakai on May 18, 2022 20:29:14 GMT -5
It pops with another speaker as well.
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Post by tjmotter on May 19, 2022 13:38:41 GMT -5
I am not going to suggest that what I am about to describe is the answer to your problem but in an interesting correlation to the work I have done on Onkyo receivers, I have seen this phenomenon on surround speakers as well as subwoofers. In every case, the root cause was blown "Mute" transistors. The function of a mute transistor is to shunt the signal to ground. When I first saw this I was surprised to find that an Onkyo receiver aggressively utilizes this function to mute the speakers during startup as well as whenever the source is changed. What I realized was that it was normal for the signal lines to generate a DC voltage. In fact, all signal lines have an electrolytic capacitor in series on the signal line. This capacitor stores a small charge and if the mute function isn't operating, it creates a "pop" sound. In a normally functioning system, the mute transistor shunting to ground discharges the capacitor which eliminates the problem.
Are there any capacitors in series with the signal line? If so, is there any circuitry that should be exercising a mute function during startup/shutdown?
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Post by tibimakai on May 20, 2022 10:13:43 GMT -5
Thanks for that idea.
Unfortunately there is no schematic for this sub.
I will have to investigate the board. I remember when we (I mean you) fixed that Onkyo, that had a bunch of those smd transistors blown.
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