Chosen Solution
This is an active subwoofer that just stopped working recently; I think the “tap” test on the post of the input RCA plug indicates that it is the subwoofer, not the amplifier, that is dead. Checked the fuse, it appears to be fine. So, after searching online forums, I began to suspect the STK404-130S IC shown in the pictures. Counting from the left, I read that pins 12 and 13 (the last 2 on the right) should have 0 v when powered (pin 5 is ground). This appears to be the case. But the discussion also indicated that there should be high resistance (essentially open circuit) between (10 & 13) and (11 & 12). This is not the case. 10 to 13 is ok, but 11 to 12 shows ~80 ohms when stabilized. I am tempted to replace this IC . . . if there is some way to check that my assessment is correct, and if there is some way to determine that nothing else is wrong. I don’t want to spend the time/money to replace it and have it damaged because something else like a capacitor or resistor is not functioning within specs.
Hi @winstontoby , Did the online information state that the reading is an “in circuit” reading or not? There may be another external (as opposed to internal to the IC i.e. faulty) circuit path between the connector pins that may be misleading you. You may have to remove the component from the board to verify whether it is faulty or not or trace the tracks from the pins to make sure that they are not connected to each other via other components, perhaps connected in parallel which will reduce the resistance reading etc. Here’s an image from the datasheet for the IC showing the internal equivalent circuit of the IC and an example (not your circuit to my knowledge) application which may be of some help.
(click on image to enlarge for better viewing) Update (11/21/2019) Hi @winstontoby, Here’s a link that has images of what cold solder joints can look like. Look for fractures in the solder, loose component leads or separation of the solder away from the track
