Anyone fixed a Paradigm Studio Sub?

[harmo]

Hi everyone,

I hope you're all well. I just registered on the forum. So please bear with me. I know just enough to get myself into trouble, and seldom enough to get out of it :-)

To get to the point, has anyone got any experience, notes, etc about repairing a Paradigm Studio Subs? They're proprietary "Class D" amps, and I can't get documentation. I'm willing to "give it a go", blindly... but I'm limited in my skills/experience. Most of my electronics involve repairing non-AC circuitry. Fault finding is something I do rarely (and never with something so complex), so I'll be blunt and say I'm almost back to a beginner state here.

I restarted dabbling in electronics after years of absence... because I've inherited some electronics gear from a pro electronics engineering friend who passed away, so I thought I should at least try to use it for something good. So I've gotten a spare moment to look at my broken subs. One of which has only died recently.

I have two similar (same series) Paradigm Studio subwoofers that are malfunctioning in different ways. One is a 15" and the other a 12". They both run the exact same amplifiers. Well... each sub back plate has two separate (seemingly matched) amplifier boards, each driving one of the two coils in each sub driver. From what little I can gather, there's some "intelligence" in there somewhere that ensures both boards are running in tandem else the whole things powers off. I mention this because....

Now, the Sub 12 doesn't show any signs of life at all, it worked and then simply stopped. I did a visual inspection, and checked the fuses on both boards of the Sub 12, the fuses are good. There are (to my untrained eye) two MOVs which I've yet to check. Can I please confirm with someone more knowledgeable how best to test these? I understand they short when triggered, but do they stay that way or are they like a resetable poly fuse? I've read a lot, but I don't do this stuff often enough to remember stuff confidently.

ROUGH PRELIMINARY TESTING:

I did some rough unpowered in-circuit DMM diode testing on the MOSFETs and other BJTs... but no sign of problems. I've inherited a Peak semiconducter tester... I thought I'd give that a go, but I have to remove the parts to test them (or so sayeth the holy tester manual). At present I've inherited a lot of test gear, but no components to speak of. I don't even have a decent resistor to discharge caps yet. I never liked the idea of simply shorting the terminals though.

The other sub is still untested.. I'm just trying to make sure I don't lose any parts. The Sub 15 has a high pitched whine, and that has bothered me for quite some time, but it continued to get worse, and now turns on and off intermittently during times of peak bass... it's like it runs out of power, then recharges, and turns back on. I'm guessing a capacitor issue, but that's pure speculation at this point.

Both use the 12V trigger, and I have tested that the trigger and power is all good. The sub 12 never turns on, and the Sub 15 tries to, but keeps turning off and on again.

Now I just want to say, that in the last 7 years, the Sub 15 amp has been sent for repairs 5 times. Several repairs involved replacing several caps, a rectifier, and blown transistors. They way they keep blowing, maybe the transistors aren't perfectly matched? Perhaps the bias is out of whack? With all these problems, I know it sounds like I'm blasting them at top volume or something, but I'm far more boring and quiet than that. I just enjoy tight, smooth bass that resonates, rather than ruins the home. :-)

The Sub 12, (bought second hand in a broken state) was repaired once already, about 3 years ago. It worked until recently, no issues, whines, or weird behaviour. They're both out of warranty, and I'm tired of sending amps (and occasionally, the whole sub) to Melbourne, only to find that the problem didn't present itself for the tech there, or the repairs don't last, etc.

Any guidance, advice, tips, arcane rituals which improve the odds of success with the repair gods welcome. Comments like "get a better sub" are only helpful if you're willing to fund one for me. Besides, who doesn't like a challenge?

Thanks for reading!
Harmo.

[Audiorepair]

If you want to learn, don't learn on something that has been repaired 5 times already.

You will just come across a whole load of other peoples' s**t and learn nothing.

[Jeff eelcr]

A good starting place is to see what was done before and recheck it.
Subs tend to loosen parts not properly attached and solder connections.
Best is always experience but pictures can help, again good visual inspection
to start.
Jeff