Hello
My subwoofer (Mordaunt Short MS909W) stopped working a while ago and I decided to finally take a look inside.
The red standby light comes on on the back of the unit but it seems to struggle to detect an input signal and activate.
I can get the light to turn green by tapping the end of the audio cable plugged into it but no sound is played out of the sub.
I've connected another smaller sub to my surround amplifier and the audio output on it seems to work fine (so looks like a problem with the sub).
I've also taken the amp out the back of the sub and connected the speaker directly to another amp and the speaker seems to work okay.
As for the sub amp itself; I've checked all 4 fuses (one in the plug, one in power socket on the back of the sub and two on the PCB) and all of them are working.
I've checked the two blue relays (one on the power delivery board and one on the main board) and the both seem to activate fine and have little resistance when activated.
I've tested the w01 bridge rectifier on the power delivery board and the kbu1003 on the mainboard and they both appear to be working fine.
There was no obvious burned components or blown caps or dry solder joints. I did replace the two large 4700uf 80v caps as they did have a very tiny bump on top (note: I haven't glued the replacements down in the pics below yet).
I have also replaced the 3 MOSFETs behind the heatsink with no difference.
I was about to move onto the 5 Op amps (NJM4558L) but could use some expertise on what the issue could be (this is my first amp I'm working on)
Update: Got it working - Q152 (A1015) failed as well as D152 (15V zener) next to it.
Bigger/more pics are available in my Onedrive album below. I couldn't find a schematic diagram for this model but did find a schematic for a similar sub which I have also uploaded (The EV SxA180 uses the same Digital subwoofer ds-300 board though the mainboard does have differences)
https://1drv.ms/f/s!AhEaoM8TIFO4niEpBhk_KlwxRhOZ
Thanks in advance for any help
My subwoofer (Mordaunt Short MS909W) stopped working a while ago and I decided to finally take a look inside.
The red standby light comes on on the back of the unit but it seems to struggle to detect an input signal and activate.
I can get the light to turn green by tapping the end of the audio cable plugged into it but no sound is played out of the sub.
I've connected another smaller sub to my surround amplifier and the audio output on it seems to work fine (so looks like a problem with the sub).
I've also taken the amp out the back of the sub and connected the speaker directly to another amp and the speaker seems to work okay.
As for the sub amp itself; I've checked all 4 fuses (one in the plug, one in power socket on the back of the sub and two on the PCB) and all of them are working.
I've checked the two blue relays (one on the power delivery board and one on the main board) and the both seem to activate fine and have little resistance when activated.
I've tested the w01 bridge rectifier on the power delivery board and the kbu1003 on the mainboard and they both appear to be working fine.
There was no obvious burned components or blown caps or dry solder joints. I did replace the two large 4700uf 80v caps as they did have a very tiny bump on top (note: I haven't glued the replacements down in the pics below yet).
I have also replaced the 3 MOSFETs behind the heatsink with no difference.
I was about to move onto the 5 Op amps (NJM4558L) but could use some expertise on what the issue could be (this is my first amp I'm working on)
Update: Got it working - Q152 (A1015) failed as well as D152 (15V zener) next to it.
Bigger/more pics are available in my Onedrive album below. I couldn't find a schematic diagram for this model but did find a schematic for a similar sub which I have also uploaded (The EV SxA180 uses the same Digital subwoofer ds-300 board though the mainboard does have differences)
https://1drv.ms/f/s!AhEaoM8TIFO4niEpBhk_KlwxRhOZ
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thanks in advance for any help
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