I used a solder gun to heat up all the cap pins on the underside of the board. Didn't bake the whole amp.
I've tried pretty much every outlet in my room. For a test I used a cheater plug without ground for testing and that didn't help.
Hum also stops if I remove the input from the sub when there is hum going on. I later noticed one night when I turned on the light so I can go unplug the sub the hum stopped so I do that now. Sometimes it takes a few tries. It's actually the same light in the room, on the same circuit. I suppose I can get a really long extension cord to try outlets on different circuits.
The hum can happen any time, sometimes I wake up or come home to a humming sub. System was not on while I was gone. At least to the best of my knowledge, no one was home or I was the only one home. Watching a movie will pretty much start it humming. I don't think it's anyone turning on the lights, as everyone is usually with me when I watch movies, or I'm home alone. Now it could be something that turns on by it self, like the fridge compressor... but seems to be too frequent when I'm watching movies.
I've had the sub for several years, and it has only started humming recently. The sub was originally plugged into the same power strip with all the equipment. After it started huming I relocated the sub trying different outlets and getting it closer to me to unplug easier.
I also got a wireless kit once to remove the direct connection between the reciever and the sub. There was no change in huming, I could also stop the hum by unplugging the rca to the sub from the wireless reciever. Cant remember if unplugging the power worked.
I have not tried leaving the sub only connected to power as it most frequently starts huming when I start watching a movie. That causes it the most, and can happen as little as every few minutes, but usually never longer than 30 minutes to start. I've recently also changed recievers to get Atmos, and for a while I had very little equipment hooked up with cables, however everything was still pluged into power outlets. Reciever change had no effect on hum. I've also changed TV's 2 recently upgrading to 4k, but the hum started well before the tv change, and still happens after.
Any tips to help solve would be appericated, I think I have the sodering and desoldering down. I did find a youtube video on removing caps and added a little extra solder to help me decoder, so tips like this is really great! Also I like to understand what people mean when they say the changed "all" the caps. A list of caps would also be helpful, I identified them as well as I can, but some were really hard to read so I could be wrong.
4 caps I cant identify are C20, C3, C9, and C52.
I used my tester on the mounted components and found higher ESR values <1 and some really high Vloss values < 20%, so I think there are some really bad caps, I just have not gotten to them yet.
The 2 caps I pulled measured with my amazon purchased lcr-t4-h, Nic 2200uf 25V 20% 85C degree caps. Checking esr chart shows it should be .06 for that size, so depending on how accurate my meter is these are boarderline? I took these measurements 1/2 a day after removing the caps giving them plenty of time to get to room temp around 80F degrees.
C45 and C46
ESR=.06 Volss 3.1 and 1891uF
ESR=.07 Vloss 3.2 and 1911uF
The 2 things that seem to help the most has been the re-soldering and changing caps.
The newer caps I put in measured about 0-.01 esr Vloss less than 1% around 2100uF and are 105C Rubycon caps I pulled from a sony car amp.
Will replace them when my new caps arrive.
After finding my sub humming this morning I unplugged and then listed to about 20 minutes of music without any hum, and so far the hum as not come back today. May try leaving it unplugged audio if I find it humming again while the system is off.
Checking with the meter I did find some caps showing <1 esr and <20% vloss, and also much lower uF than listed on the cap, but think it might have been parallel readings with other caps on board and have not found the really bad ones yet.
I could potential have a ground loop issue in addition to the capacitor issue. I threw on a movie today, and played some more music and did not have any hum.
Last edited by LotsaBoxes; 07-17-2018 at 04:53 PM.