I received this woofer from a customer who wanted it checked by a technician.
He hinted that the woofer was from another technician who was not able to repair it.
Items from other technician are tricky to repair especially if the tech had limited knowledge on how circuit works, they ends up making so much experiments and guess works and therefore chances of repair is quite low.
Nonetheless I decided to have a try and see if I can help this customer who seemed desperate to see his machine back to normal status.
After opening the set I found the main filter capacitor rated 470uF/25V has its top part swollen.
From the symptoms at hand the failure of this capacitor fits so well and I was very confident this was one of the easy fix.
I pulled a replacement capacitor from my capacitor kit quickly and decided to do test and the machine came up beautifully.
I decided to continue listening the soothing music from the machine as I continued with other repairs.
After about 30 minutes, the humming sound was back, I decided to open the set and see if the same capacitor has failed again.
I noted the capacitor was still holding strong, no signs of stress and decided to use touch method to pick up any component which may be overheating.
I started with the audio I.C and found it extremely hot, I suspected it instantly but continued with my touching method and placing my finger on top of the main filter capacitor which I have just replaced also found it very hot, touched the bridge rectifier and also found it un usually hot.
I decided to change the Audio I.C directly but before that I decided to power the woofer one more using the DC power supply since the woofer was using due power(AC and DC).
I run the machine for nearly one hour and this time that machine was running cool, all components.
This made me rule out all the suspected components, Looking closely at the transformer connector I noted it has some burnt marks and was not happy with this, I suspected the transformer is failing under load and to confirm this I decided to run the machine again for 30 minutes and feel the state of this transformer, after running the machine for 30 minutes, I touched the transformer and found it un usually hot.
I decided to do direct replacement but since I did not have this part in my workshop I decided to go buy one in town.
I replaced the transformer with a new one and again run the machine for one hour and the machine was still working well.
I again did the touching process and all components were running cool.