Electronics > Repair

subwoofer amp repair

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electrolust:
Had a power outage recently. When the power came back on, I lost the dishwasher and my subwoofer power amp. I am not sure that the power amp was working before the outage. It was in storage for awhile and I had a little downtime so was working on setting it up. It definitely worked when I put it away a few years ago. It is about 15 years old and I used it for about the first 8 years then stored it. It was plugged into a surge suppressor / PDU type device and everything else survived, although everything else are super modern devices, all new (and newly designed) within a year ... so very modern products, maybe all with excellent TVS protection. It's the age of the amp mostly that leaves me unsure whether it was the outage recovery that killed it. Everything is plugged into the PDU "unswitched" or bypassed from PDU control, which maybe also bypasses the surge protection.

The amp is an artison RCC-600-SA. It complements my RCC-600-SM subwoofer pair so I'd like to keep this amp. It drives a pair of 8ohm amps in parallel. It is spec'd for 600ohm RMS into 4ohm and designed to bridge the pair of matching subs. It has some EQ built in which matches the subs, which is why I would like to keep it. You couldn't normally buy the sub and amp separately back when this was on the market.

I do see one obviously damaged component, looks like a ceramic cap. (This also suggests to me it was the power recovery.) I guess I should test the nearby caps and assume they are identical? While I'm there should I replace the electrolytics? There are a number of large ones (10000uF) near the damaged ceramic, then another set of medium looking ones nearby, and lastly maybe a dozen pretty small ones on the input board which also contains phase and low pass filters. None of the electrolytics look bad. I could test them but really at that point why not just replace.

Anything else I should proactively replace, considering the likely cause of failure? What I guess is the mains regulation and a large toroidal transformer both look perfect visually.

electrolust:
I guess if there is a TVS device somewhere I should replace that?

dietert1:
The blown part may be a small ceramic capacitor. Sometimes those go bad. If you take them away and replace the mains fuse in case it is blown, does the amplifier turn on? What is the symptom? Without schematic, the repair can be a bit of try and error.
The big power supply capacitors are less prone to getting dry than the small ones. I would do the caps after the repair, in order to avoid a difficult to solve double error situation.

Regards, Dieter

TheMG:
That ceramic capacitor looks like it burnt up a long time ago, I see some hair and dust in the burn hole, which most certainly has ended up there after the event in which it burnt up.


--- Quote from: electrolust on October 28, 2021, 08:01:30 am ---Anything else I should proactively replace, considering the likely cause of failure? What I guess is the mains regulation and a large toroidal transformer both look perfect visually.

--- End quote ---

Don't "proactively" replace anything just yet. Troubleshoot!

Get your DMM and start measuring. First, is that ceramic capacitor shorted or has it blown open-circuit? If it's open, it's likely not causing the problem (based on its location, its purpose is likely for a bit of extra high frequency bypassing in the power supply, not a critical function). It should eventually be replaced as it is obviously faulty, but may not necessarily be the cause of the amp not turning on.

Fuses - have you looked around for fuses and tested if they are any good? If fuses are good, start checking voltages. Where do you have power and where do you not. Analyze the basics of how the circuit is probably supposed to work. For instance, is there a standby supply and relay or is the main toroidal transformer supposed to always be energized?

electrolust:
Thanks, very helpful. Yeah I now realize it's likely old damage. The fuse should have popped if it was a line surge.

OK will start with some basic troubleshooting.

I maybe should have noted first, the amp does power on, including in response to 12v trigger if I put it in that mode. It just doesn't produce output. There's also a signal trigger which I didn't think about trying so I'll make sure that part works (or not) also, which might help narrow it down.

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