Fu Jun Fun

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Robert R
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Fu Jun Fun

Post by Robert R » Wed Apr 22, 2015 4:57 pm

Loving my Craigslist Sunfire MkII True sub, now that it's working right. It came pretty cheap, and sort of working, but all sorts of problems. Like most at this age, it had the coming on - staying on difficulties. Also had hum, random grumbles, and pretty bad distortion on the really low pedal notes, down in the 20s. And if you gave a tap to the center of the woofer, it responded with a loud burst of low frequency energy - backtalk, I suppose you'd call it - an electric power assisted drum!
All this is symptomatic of bad electrolytics - the 15 year old Fu Jun capacitors all are dying; in fact some were already dead. I suspect they were not all that great when they were new, 15 years ago. A couple I removed had one lead just fall out. Even with the leads, one 100 μF was hardly even a cap at all anymore - I don't know what you'd call it. Not open, but floating a reading of 4 to 6 μF. In my experience, if a simple cap checker reads these min-lytics at anything less than their rated capacitance, replace them. Most of the ones I removed were way under value, and replaced with 105 degree Panasonics. In general in these subs it's not the two biggest caps, and not so often the little 1, 2.2, and 4.7 sizes, but every damn size in between.

On the amp board are half a dozen filter caps, in the low voltage regulated supplies. ALL of those were bad, including one really bad in the (-) downconverter driver circuit. I really don't know how this poor thing worked at all And the two caps that serve in the auto on/off circuitry were junk, too. Nice to have that working again. Comes on instantly, and shuts off only after about 7 minutes of no signal.
On the preamp board were several more losers, again mostly p/s filters.

I kept testing it after replacing a few caps, run it a bit, then back to the bench, and first discharge the one big cap that wants to kill you {I used a 1K 5 watt resistor - takes it down in about 10 seconds or less.}, then replace a few more. Gradually it got better.

Did over twenty caps, and I'd have kept going and changed out every single one, except the work is so miserable. The boards have foils above and below, and clearing the holes of solder is a problem; just getting your fingers in places to pull out the parts is a problem [I didn't want to separate the boards from each other - just worked with the whole plate amp intact]. Soldering the standup caps to the top foils where necessary is a real challenge, if you want them anything like flush to the board. I got it working very well about the same time I ran out of cuss words, so that seemed a good time to quit.

Next one like this goes to Bill Flannery - what he does is really worth what he charges, at least when there is this much shit wrong. And he ships it back about as quickly as you can get an order of capacitors.

RobertR
"You know what folks? I'm happy."

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fill35U
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Re: Fu Jun Fun

Post by fill35U » Thu Apr 23, 2015 1:30 pm

I hear ya- exactly how it went with mine. Sunfire really dropped the ball when it came to electrolytic caps.

And I'd agree that Flannery is worth every penny on these subs! Sometimes the aggravation of DIY isn't justified by a little cost savings.

Glad you got her up and running! :)
Living room system: TGP IV, TX-8r, TD-1400, PT-2400(x6), PM-1.5a(x3), TFM-45(x2), TFM-55, Silver Amazings Mk IV

Spares/projects: C-9, M-400, PM-350(x2), M-1.5t(x2), PT-2400(x2-1/2), PT-1800(x4), TGP I, Architectural True Sub, pm420

OconeeOrange
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Re: Fu Jun Fun

Post by OconeeOrange » Fri Apr 24, 2015 3:19 pm

Flannerty is the man.

I have never owned a Sunfire sub, have a "Carver" one.

I am amazed at how often these are on ebay.

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