need some help repairing a Jamo SW 3015 active sub  - Page 1
Forum section: electronics / repair

author: khalidlib
author_rank: Newbie
timestamp: September 10, 2021, 04:16:55 pm
content: hello everyone i am new to this forume, came here as per the advice of some frinds, hoping to find some help repairing an active sub woofer i have for more than 10 years now, it is the Jamo SW 3015 active sub woofer 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 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 subwooferstill 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 things1- the 084C ICs on the small board get hot2- in the small board the continuity test between column A and column B is + except for the signal line there is no continuity3- it is printed in stencil on the board that Red line in column A is 12v but i could only mesure 6v4- the led terminal on the control board measure 2.6v when it is floating but when i connect the led to measure 0.6vso i am asking for help again pleasei am hoping someone with some knowledge or had a similar problem and fixed it could help me out no how to proceed to troubleshoot and fix the problem

author: EHT
author_rank: Frequent Contributor
timestamp: September 12, 2021, 09:02:43 pm
content: Can you show the audio signals on a scope, say output of the preamp etc? I suggest first understanding what type of amp that is and trace the schematic out if you cannot find a copy of it. I suppose class D as it has MOSFETs. Check you are aware where any high voltages are present before taking any measurements with it on.From my experience with a Velodyne one, I suggest that if the amp and PSU are boxed into the speaker cabinet with no ventilation, just rip it out and use an external amp.

author: khalidlib
author_rank: Newbie
timestamp: September 12, 2021, 11:47:50 pm
content: hello, unfortunately i don't have an oscilloscope and i could not find schematic for it antware, and yes it is like you said the amp and PSU are boxed into the speaker cabinet with no ventilation, but 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, giving out 12v line and tow 22v lines no problem thare, 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 valuethis 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

author: EHT
author_rank: Frequent Contributor
timestamp: September 14, 2021, 09:44:00 pm
content: If it isn't a power supply problem and you don't have any luck finding a failed component directly (e.g. diode-test, physical damage) then your ability to diagnose it is going to be severely limited without a scope and without the schematic. You can trace the schematic back from the PCB if any unusual parts can be identified. Obviously that is laborious, but if you don't want to give up and use it as a passive box then that is your way forward.If you post up the schematic and annotate it with waveform measurements then you could expect a lot of people to chip in with ideas. Without this, there's nothing to go on...BTW, you can find plenty of advice about acquiring scopes here too. First, check if the power supply of this thing is isolated from the mains supply. If not you will either need a battery powered scope (e.g. Fluke Scopemeter) or a High Voltage Differential probe. Both of these add expense but you can find old scopemeters in the range £100-200.