Audible clicking from Definitive Technology SC 2000 Subwoofer amplifier - Page 1
Forum section: electronics / beginners

author: g.costanza
author_rank: Contributor
timestamp: September 11, 2023, 05:13:11 pm
content: I am an novice, but I'm learning.12 yr old Subwoofer driver developed a constant popping sound, even when nothing plugged into the single audio input jack.Unit doesn't have a power switch. It powers on when you plug it into AC mains and turns off eventually when not fed a signal.Plugging it into AC mains now with nothing plugged into audio input, the power led flickers in sync with the popping.I opened the enclosure, disconnected woofer, and I can hear a faint clicking from the PS itself.Here's a video I made...https://youtube.com/shorts/x08iCv3QHL4?feature=shareI've done some probing of components on the main PS board and haven't found anything yet. I haven't found anything obviously shorted or open.About to start de-soldering caps to test out-of-circuit. I do have a transistor/parts tester.I don't see an IC on the main PS board (which is mounted to the bottom of the subwoofer cabinet). I'd assume it would need one.This board does connect to two smaller boards that are attached to the rear "plate" where the power LED, volume knob, input jack, and AC power socket are mounted.The cable connecting the main PS board and the secondary board has 4 wires marked HD+, AGND, HD-, and OPTO.I'm wondering if this cable is communicating with the IC chip.

author: u666sa
author_rank: Frequent Contributor
timestamp: September 11, 2023, 05:25:41 pm
content: Capacitors. Best way is to usethismeter to check ESR, it's cheap enough. But if no $$$ just replace them all -- but beware, caps you buy new sometimes are bad.

author: g.costanza
author_rank: Contributor
timestamp: September 11, 2023, 06:36:35 pm
content: I'm using the mk168 transistor tester. It seems to work ok.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 11, 2023, 06:54:40 pm
content: Sounds like an aging power supply. The capacitors are probably kaput.

author: g.costanza
author_rank: Contributor
timestamp: September 12, 2023, 01:21:09 pm
content: I tested all the caps (while in circuit) on the main PS supply board with my MK168 and they all tested good. Thinking the meter could have been wrong at least once, I removed each cap independently, tested it, and wound up putting them all back because the meter was correct to begin with. The only two caps I didn't remove to test was a pair the really large ones where surprisingly the leads are so big that my iron couldn't get the joints to melt, but they did measure good in circuit.I also measured the caps on a secondary board. Of the caps that the MK168 recognized as capacitors on that board, they al measured good. A few were recognized by the meter as diodes.Anyone know what that means?Can I force the meter into being just an ESR meter, vs it's auto recognition setting?There is a third board that has the power LED, input jack, and volume knob. I disconnected it and that didn't change the amp's behavior.THANKS!

author: g.costanza
author_rank: Contributor
timestamp: September 12, 2023, 02:58:12 pm
content: Here's another vid showing the amp pulsing DC voltage up to 55mv to speaker output....https://youtube.com/shorts/98ntDWhUVGs?si=OpazRhYt-ruBP2CCIt corresponds with the popping from the driver when it's hooked up. Does that help diagnose?I've also order this ESR meter...https://a.co/d/4UW3bJQI watched a few reviews and like the tweezer design and the ESR graph.