Help is needed to fix Dali Sub E-12F which had no +/- 15V at the printed circuit board assembly (PCBA)。
Also, there was no Standby Mode Indicator illuminated at Front Speaker Cabinet !!!。
Without a schematic, I noticed that there were 2 chips on this Sub (LNK364PN on the Main Board) and (IR2153S located at Side Board with its 7 pin connectors mounted onto the Main Board)。
I have no clue on how to start troubleshooting this Sub !!!。
Look forward to receiving guidance soon。
Thanks in advance。
Most subwoofers use a switched mode power supply which are much more difficult to diagnose than linear power supplies. Not really something for a novice to try and repair. You need a good understanding of how switch mode power supplies operate and how to recognize the various sections on the circuit board.
The most common items to become defective are the output transistors in the amplifier section and filter capacitors in the power supply. The transistors can be checked for shorts or opens using a digital mutlimeter on diode mode. This may require unsoldering the transistors which can be a major hassle in subwoofers as they are often covered in epoxy to prevent vibration. It is more likely that the power supply is the issue, but I always check the transistors for shorts as a precaution (this can be done in-circuit). [Actually, I looked at the subwoofer description and it uses class D amplifiers. If they use class D modules and not discreet components, you won't be able to repair the amplifier section.]
Sometimes you can get lucky and the capacitors will be visibly defective. The electrolytics should have flat tops and no signs of leakage. If the tops are bulged or there is electrolyte leaking from the bottom, they are bad. I recently repaired a computer ATX power supply by replacing the 3 visibly bad capacitors and it has been working fine now for weeks. A single bad cap will stop the switch mode power supply from working. As ATX power supplies are switch mode, you can study ATX power supply repairs and apply that knowledge to fixing other switch mode power supplies as the general principles are the same. There is a YouTube channel called Learn Electronics Repair and he has a lot of good tutorials. Look for the ones on ATX power supply repair as he also draws schematics and explains how they operate. The most detailed is this one:
