Here's a link to a video I made.
Speaker makes popping noises as soon as the subwoofer is plugged in.
It doesn't have a power switch. It senses signal and turns itself on.
I took it apart and the PS is making clicking noise.
I suppose this can be the relay, but I've also read it could be arcing in the transformer.
I've read that a bad diode in another brand of subwoofer with auto-on was causing that sub's issue.
But I've also read that a switching PS will do what mine is doing if it isn't getting enough voltage.
Video
Speaker makes popping noises as soon as the subwoofer is plugged in.
It doesn't have a power switch. It senses signal and turns itself on.
I took it apart and the PS is making clicking noise.
I suppose this can be the relay, but I've also read it could be arcing in the transformer.
I've read that a bad diode in another brand of subwoofer with auto-on was causing that sub's issue.
But I've also read that a switching PS will do what mine is doing if it isn't getting enough voltage.
Video
"But I've also read that a switching PS will do what mine is doing if it isn't getting enough voltage."
Or there is a current overload.
Or there is a current overload.
Yes. Over voltage or under voltage.
I hooked up my MM up to the woofer output terminal and the amp is pulsing between 0 to 50mv of DC. Don't know if 50mv offset is normal. I know ppl have said it shouldn't be more than 40mv. While searching this topic I ran across someone attempting to fix another Def Tech sub amp and ppl were saying the 50 mc he was seeing could be normal.
I hooked up my MM up to the woofer output terminal and the amp is pulsing between 0 to 50mv of DC. Don't know if 50mv offset is normal. I know ppl have said it shouldn't be more than 40mv. While searching this topic I ran across someone attempting to fix another Def Tech sub amp and ppl were saying the 50 mc he was seeing could be normal.
There is no IC on the PS board that I can see. There are 3 boards in this subwoofer enclosure. One small one has the input jack, power led and volume. It's connected to a second smaller board that appear to be the "amp", but I think it may also have the SMPS's IC chip as I don't see one anywhere on the main PS board. The connection from the main PS board and the "amp" board is connected by a 4 wire connector labeled HD+, HD-, AGND, and OPTO. Is the OPTO sending or receiving a signal from the octocoupler as part of the feedback loop? There are 2 octocouplers on the main PS board, beside each other. HD+ and HD- might just mean "Class HD", as that is printed on the boards like a marketing name for the tech they're using.
The amp needs powering somehow so I guess HD+ and HD- are positive and negative rails.
What voltage you get between hd+ and hd- and agnd ?
What voltage you get between hd+ and hd- and agnd ?
I'll check when I get home.
I will say I went around all the boards checking all the devices that looked like 3 legged "transistors". They all seemed to measure ok (as far as my limited knowledge would allow) except for 2 that are on a heat sink, beside a pair of large caps and next to the HD+/AGND/HD-/OPTO connector. The outer pins on both devices measured as if they were "shorted" to one another. I removed them from the board and heatsink and measured them and they no longer showed that "shorted" measurement. They measured like a pair of diodes connected to the center pin, so I reinstalled them.
One other measurement I was not
expecting was the pair of optocouplers. I measured them with power OFF and in circuit. They measure like diodes on the emitter side. On the sensor sides, one measured "open" in both polarity directions. The other one acts like it is coupled to a cap because I get a rising voltage in both polarity directions.
I did remove all but the largest pair of capacitors from the main PS board and tested them on a MK168 parts tester. Their capacity and ESR were all normal. I tested the pair of largest caps in-circuit because I couldn't remove from them board due to the heat required to desolder them wasn't happening with my budget soldering iron. They also measured normal.
I will say I went around all the boards checking all the devices that looked like 3 legged "transistors". They all seemed to measure ok (as far as my limited knowledge would allow) except for 2 that are on a heat sink, beside a pair of large caps and next to the HD+/AGND/HD-/OPTO connector. The outer pins on both devices measured as if they were "shorted" to one another. I removed them from the board and heatsink and measured them and they no longer showed that "shorted" measurement. They measured like a pair of diodes connected to the center pin, so I reinstalled them.
One other measurement I was not
expecting was the pair of optocouplers. I measured them with power OFF and in circuit. They measure like diodes on the emitter side. On the sensor sides, one measured "open" in both polarity directions. The other one acts like it is coupled to a cap because I get a rising voltage in both polarity directions.
I did remove all but the largest pair of capacitors from the main PS board and tested them on a MK168 parts tester. Their capacity and ESR were all normal. I tested the pair of largest caps in-circuit because I couldn't remove from them board due to the heat required to desolder them wasn't happening with my budget soldering iron. They also measured normal.
The power supply cutting in and out is usually sign of a short.
So things like shorted electrolytic or output transistors or driver transistors.
So things like shorted electrolytic or output transistors or driver transistors.
Ah. Ok. I'm curious why none of them measured as "shorted" on any of the 3 boards except for those two that didn't measure shorted when taken out of circuit. "Shorted" would emit a constant tone on my fluke meter in diode mode, correct? I either got the .xxx voltage reading with a short tone as you would expect on a diode, or an open reading and no tone.
Ok. Here's a video of the clicking noise, showing the DC pulsing on the speaker output.... video
I measured the output from the HD+ and HD- and they also pulse, or "increase voltage", with each successive click.
It goes from around 9v to 40v, (example... 40V on HD+ and -40V on HD-).
If you watch and listen to the video, the clicks are constant (like "in time")and it's like there are 6 clicks. 4 as the voltage rises, and then 2 lower level clicks as the voltage drops, before it rises again. and so on...
I measured the output from the HD+ and HD- and they also pulse, or "increase voltage", with each successive click.
It goes from around 9v to 40v, (example... 40V on HD+ and -40V on HD-).
If you watch and listen to the video, the clicks are constant (like "in time")and it's like there are 6 clicks. 4 as the voltage rises, and then 2 lower level clicks as the voltage drops, before it rises again. and so on...
And these are the part numbers (BYV32E 200 PJA1921 C4 9115) on the only two transistor type devices I measured in the whole amp/power supply that had a "short" when tested in circuit and no fault when measured out of circuit.
Here is a link to schematics...
https://drive.google.com/file/d/1XnZUAmbdtXThbPE7MGXmsgxzh-rNIC1q/view?usp=drivesdk
https://drive.google.com/file/d/1XnZUAmbdtXThbPE7MGXmsgxzh-rNIC1q/view?usp=drivesdk
This was designed by a company started by John French. He is a talented and creative designer.
He did a lot of interesting work with tracking power supplies in years gone by.
The down side of his designs is they are often not garden variety typologies and so can be very challenging to understand and repair by the average teck.
A faulty amplifier section could well be the cause of the power supply not starting up.
With John's work expect subtle details and things to be "different" than expected.
He did a lot of interesting work with tracking power supplies in years gone by.
The down side of his designs is they are often not garden variety typologies and so can be very challenging to understand and repair by the average teck.
A faulty amplifier section could well be the cause of the power supply not starting up.
With John's work expect subtle details and things to be "different" than expected.
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