Hi everyone, i’m hoping some one has the patience to point me in the right direction to repairing this fairly expensive boston acoustic msub
first the off/on/auto switch was busted so i forced it into auto mode by bridging a connection on the main board and now the blue light comes on but i don't get any audio output. Does anyone one have any experience repairing this amplifier or even a schematic? I believe this unit is very similar to the boston acoustic HPS10, HPS12 highout subs. There’s a few schematics of the HPS floating around but the preamp section is blurry and i can’t read alot
of it so maybe some one has a better quality one? I looked it over, checked some the mosfets, some of the power resistors and cleaned that nasty conductive epoxy glue stuff off but not having much luck in the trouble shooting department. The mosfets are heating up the heat sink to a normal temperature when i try to play a song so im leaning towards and issue with the preamp section
I did however find a part of the PCB that was discolored from heat that may be an area of interest. It consists of two transistors which you can see in the short videos i attached along with some pictures to my google drive.
As i was investigating the issue i notice some resistors and capacitors appear to be missing from the preamp board but it’s hard to tell if they broke off or if they were intentionally left off (see attached pic)
C263
R238
C259
R282
Boston MSUB board photos
first the off/on/auto switch was busted so i forced it into auto mode by bridging a connection on the main board and now the blue light comes on but i don't get any audio output. Does anyone one have any experience repairing this amplifier or even a schematic? I believe this unit is very similar to the boston acoustic HPS10, HPS12 highout subs. There’s a few schematics of the HPS floating around but the preamp section is blurry and i can’t read alot
of it so maybe some one has a better quality one? I looked it over, checked some the mosfets, some of the power resistors and cleaned that nasty conductive epoxy glue stuff off but not having much luck in the trouble shooting department. The mosfets are heating up the heat sink to a normal temperature when i try to play a song so im leaning towards and issue with the preamp section
I did however find a part of the PCB that was discolored from heat that may be an area of interest. It consists of two transistors which you can see in the short videos i attached along with some pictures to my google drive.
As i was investigating the issue i notice some resistors and capacitors appear to be missing from the preamp board but it’s hard to tell if they broke off or if they were intentionally left off (see attached pic)
C263
R238
C259
R282
Boston MSUB board photos
Attachments
yup, didn’t get much help but i figured it out on my own. Read through this thread it should point you in the right direction https://www.eevblog.com/forum/repai...-acoustic-msubwoofer(no-sound-output)-(pics)/ good luck
Thanks! I just started a thread on it. I will check those caps. Mine I can hear the class d board whine when on and the caps on it get pretty toasty. :/
mine was doing the same! Also take time to remove all that nasty brown epoxy as it can become conductive over time
i also replaced the 4 power resistors too because the coating started coming off after removing all the glue during trouble shooting. Here’s some more pics that might help. I also have some pics of the class d amp board if you find something for burnt up on it. The amplifier section schematics are not available to us, not even boston acoustics has them anymore
Attachments
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That was totally it, thank you! couple of the 100uF 16V caps had degraded to nF ranges. =( I didn't even notice I wasn't getting relay click before replacing them.
That said, those damn caps are a pain to replace. pulled up a couple traces in the process (thankfully didn't break them). Will use hot air next time, or try just twisting them off then remove what's left.
Thanks so much!
That said, those damn caps are a pain to replace. pulled up a couple traces in the process (thankfully didn't break them). Will use hot air next time, or try just twisting them off then remove what's left.
Thanks so much!
glad you were able to find out the issue! I just twisted them off with pliers then removed the remaining leg with the soldering iron. Twist a little bit one way then a little bit the other way and keep doing this till it comes off