Hi all, I am having an issue with my Martin Logan Depth I subwoofer. Let's start from the beginning. I found out that my sub was damaged before covid era. Took time to look inside the sub and found out lots of corrosions on the boards..some of the connectors shows signs of burnt ! Called ML back then and was told no parts available during covid due to shortages of parts. Fast foward to today. ML finally got me the power supply, amplifier and the top assembly boards totaling about $700! The good news is the sub is back in action. But the bad news is sub is acting wierd......meaning all 3 woofers would sometimes vibrating without any signal at all. The vibration stops when I put it in standby mode. I also think that when I play the music, the woofers is vibrating even there are no big bass going on. I also notice continuous thumping sound coming from inside the cabinet. The woofers also making continuous clicking sound when the issue arises. When I switch to auto mode, the sub is having trouble recognizing the signal from the source ( the led light keep switching from orange to green back to orange...) I noticed the outer wrapping of the transformer is slightly blackened. Is the transformer bad too?? The problem is intermittent...sometimes I turn it off and it goes away but may come back.. So to wrap it up. Do I have 3 bad woofers? Should I try replacing the transformer and also all the connectors and hopefully fix the issues? I don't have any electrical or audio engineering background. Just swap and plug type of guy. Please help!!
With the Martin Logan Depth i Subwoofer being servo controlled, this sounds like low frequency instability due to insufficient phase margin in the motional feedback circuit. You can test this hypothesis by disconnecting the servo feedback by removing the plug with the woofer servo sensor wires from the board. If this stops the vibrating without signal input, then this is the problem.
I don't have a picture of the "Depth i" board, but here is one for the Depth showing the servo sensor wires are plug 3. You should be able to identify a similar plug on yours, having 2 thin wires coming from each woofer. Feel free to post a picture of your board if you are unsure.
One thing that can reduce phase margin at low frequency is if one of the woofer sensors is not connected. You mentioned seeing signs of corrosion. You might try using contact cleaner on the sensor plug connector pins to make sure all 3 woofer sensors are getting their signals connected to the pre-amp circuitry on the board.
what if I unplug all 6 servo wires on the speakers? would that work too if I can't locate the sensor plug. I also notice when I switch to auto mode instead of on or standby, the led light switch back and forth between orange and green.. with clicking sound and vibration from all 3 woofers when green and no activity with orange led.
It would be best to unplug the sensor plug at the board to minimize noise pickup by the sensor preamp. If you want to unplug them at the speakers, I would recommend hooking the 2 connectors together once removed from each speaker to minimize this noise pickup. Of course your mention of the sensor connectors at the woofer brings up another locations that corrosion could be causing a problem. Be sure to use contact cleaner there as well if you see corrosion.
I don't know for sure what is going on with the led light activity. It might be related to some protection circuitry that is getting triggered due to the instability of the servo control. You will have to wait and see if it is still a problem once you get the sensors disconnected.
I don't know for sure what is going on with the led light activity. It might be related to some protection circuitry that is getting triggered due to the instability of the servo control. You will have to wait and see if it is still a problem once you get the sensors disconnected.
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Unplug the sensor plug did not solve the problem. I also observed the sub took a minute or two to juice up the sub..and it starts with one or two loud thud thumping like sound before working. The vibration seems to happen after maybe like 30 minutes of playing and will keep vibrating after I cut off the signal. I currently only go up to level 2 or 3 which is enough for my listening style...........wondering the minor vibration will actually affect the quality of the bass note if I can't fix the problem?
Ok, so not an instability issue with the servo. At least it was easy to test.
I jumped to that conclusion based on your description of vibration, which I took to mean motion that was low enough in frequency that it didn't produce sound you could hear...otherwise you would have likely described it as humming or buzzing. Does the vibration produce sound you can here? Based on your latest description of changing noises and symptoms you might have a lot of bad connections between boards from corroded connections. That is about all that is left since you replaced all of the electronic boards, right?
I jumped to that conclusion based on your description of vibration, which I took to mean motion that was low enough in frequency that it didn't produce sound you could hear...otherwise you would have likely described it as humming or buzzing. Does the vibration produce sound you can here? Based on your latest description of changing noises and symptoms you might have a lot of bad connections between boards from corroded connections. That is about all that is left since you replaced all of the electronic boards, right?
Latest update…. The sub is not working!! I opened up the sub and noticed the amplifier board green led is not lid. Meaning no power to the board? I am now suspecting the harness could be the issue? This one goes from power supply board to the amplifier board. The original amplifier board power connector got burned to the ground
and causing the blackened connector as shown in the picture. Can the harness be rebuild… where do I even find the exact same connector and pins?
and causing the blackened connector as shown in the picture. Can the harness be rebuild… where do I even find the exact same connector and pins?