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Old 09-10-2021, 05:32 PM   #1
khalidlib
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Default need some help repairing a Jamo SW 3015 active sub

hello everyone i am new to this forum, came here as per the advice of some friends, hoping to find some help repairing an active subwoofer i have for more than 10 years now, it is the Jamo SW 3015 active subwoofer with THX dedicated input , it was in storage for about 3 years since i moved to a new place, and i decided it is time to put my home theater back up ,however after bulging it in the sub and hooking it up to the amplifier pre out it did not make any sound , the on standby light came on but no sound with a faint buzzing sound coming from the amplifier plate, i turned it off and back on again and same story, then the ON indicator light went off but still the buzzing noise is their, like a small running fan blade hitting a small wire, i took the plate off but there was no fan and the noise is coming from the preamp board or the power supply unit , can't tell for sure but if i disconnect the power from the supply to the amplifier unit the buzz stops, all caps look ok and no burn marks anywhere, after asking around it appeared it was the capacitors at the hi voltage mains input , changed one and the buzz went away, i ordered a better quality and i will put them in when they arrive, sadly that did not fix the subwoofer
still no sound and the indicator led would not come on, i left no stone unturned, looked everywhere for schematics and could not find anything as far as my knowledge goes apparently it does not go very far.
i made a crude sketch of the connections and ics on the board for reference and i noticed a few things
1- the 084C ICs on the small board get hot
2- in the small board the continuity test between column A and column B is + except for the signal line there is no continuity
3- it is printed in stencil on the board that Red line in column A is 12v but i could only mesure 6v
4- the led terminal on the control board measure 2.6v when it is floating but when i connect the led it measure 0.6v
so i am asking for help again please


i am hoping someone with some knowledge or had a similar problem and fixed it could help to guide me out no how to proceed to troubleshoot and fix the problem
thank you guys
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Last edited by khalidlib; 09-10-2021 at 05:34 PM..
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Old 09-12-2021, 03:26 PM   #2
momaka
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Default Re: need some help repairing a Jamo SW 3015 active sub

Hi Khalid,
Have you checked that the PSU is outputting proper +/- 22V and also +/- 12V supplies when the PSU is not connected to any other board on the rest of the amplifier? If not, perhaps start there to see if the PSU is behaving properly. I'm not particularly familiar with the Jamo SW 3015, but a lot of subs from that era have an auto turn-on feature when they receive an audio signal. The key to that working are stable minor rails - in your case, the +12V and -12V rails, I think. The fact that the 084C ICs are running hot suggests there may be a problem with the +12V or -12V rails. Of course, if there are any other regulators check and make sure those are working too.

When you said you recapped the unit, I imagine you mean only the power supply? If yes, then that leaves the possibility of one of the small caps on the signal board to still be bad. To quickly find out, though, connect all of the boards the way they should be, then take a hair dryer and heat the signal board to about 50C. After this, see if the amplifier still buzzes and/or wakes up.

Let us know what you find after this.
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Old 09-12-2021, 06:13 PM   #3
khalidlib
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Default Re: need some help repairing a Jamo SW 3015 active sub

thank you momaka for that tip, i only recapped the hi voltage side of the PSU, and that stopped the buzzing.
i only have one rail for the 12v coming out of the PSU but i got 2 rails outputting +22v from 3 wires, measuring the output is 23.6v if the PSU is not connected to any other board but after i connect all the boards it measures 22v

the amplifier board carrying the p55ne has another 12v regulator on it, tracing the output of that regulator it is supposed to supply 12v to the red wire connecting the amp board to the small board that has the tow 084C ICs but it is not doing that, on further checking, the regulator is not getting any voltage to the pin1, i decided to recap the amplifier board removing that wight glue they use may reveal a leaking cap or something

unfortunately i don't have an oscilloscope and i could not find schematic for it antware, i wish that i could just use an external amp, this subwoofer has a servo drive, an external amp would make it clip, besides i like to keep that feature, it is why i bought it.
the PSU is working properly as far as i can tell, giving out 12v line and tow 22v both lines are positive lines , understanding the integration of the amp with the servo electronics and signal sensing is the puzzle for me, i want to think that the small board with the 084c ics is the servo differential log sensing unit but the servo wires coming from the piso on the wafer are going in the control board that makes it hard to figure out the break point in the circuit.
i took it to several repareshops but they would not accept it, i contacted Klipsch asking if they could provide a schematic or if they could sell me a replacement plate, but never got an answer, i really like this sub, and it has a sentimental value
this is why i came here looking for guidance help, i was told this forum has the best of the best electronic wizards on the internet
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Old 09-16-2021, 05:40 PM   #4
momaka
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Default Re: need some help repairing a Jamo SW 3015 active sub

Quote:
Originally Posted by khalidlib View Post
the PSU is working properly as far as i can tell, giving out 12v line and tow 22v both lines are positive lines
Are you sure about those rails?
On the original diagram you drew, you indicated two 12V rails going to the signal board - one positive and one negative. Make sure both of those rails are present, stable, and equal in value. With so many op-amps on the signal board, it just has to have a +12 and a -12V rail. I would be very surprised if it doesn't. As for the 12V rail from the KA7812 - make sure that one is also good. Without everything present for the power rails, we can't get anywhere.

After that, you can insert an audio signal into the signal board and see if you can trace it around. No oscilloscope - no problems! An old pair of headphones may do the trick. Just put 100 Ohm resistors in series with each headphone driver. That way, if you accidentally touch something with higher power, it won't blow up the headphones (and possibly make you go deaf. )
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