Gotta love fleaBay - the other week, i nailed a pair of these 6.5" monitors with one woofer dead, for a measly 142e incl. shipping (117gbp from the UK, ~180$) - they (still) retail for a tad over 300e 
The ad said the bad woofer measured 0 ohms. Being the curious type, i measured both woofers myself, but my meter actually said "OL" on the bad one, ie. open-circuit.
The culprit turned out to be the broken joint where the woven tinsel lead (from the spade connectors) met up with the wire coming from the voice coil. a drop of flux, some "keyhole surgery" with the soldering iron, and a shovel of cyanoacrylate on top to secure the joint, and...
*Drumroll, please...* IT WORKS!...
Preliminary testing - terminals hooked up to my oscilloscope, slow sweep, "manually" wiggled the cone => wiggle of the trace on the scope screen
Oddly enough, my DMM couldn't get a steady ohm reading (wobbled between ~2 and ~12 ohms), but after i hooked it back up, it sounds and plays just fine
While they were still "on the way", some googling revealed "horror stories" about some PSU design fault (they have SMPS's inside) that lead to the "cooking" of the startup cap. Mine seem to have some newer revision, and the hot resistor and the startup cap are nowhere near each other Amp board silkscreen say "2003", PSU board says 2009, plus a 2010 date stamp on the bottom.
As long as i had them opened up, i decided to re-cap the PSU boards as well. All "FuhYin" caps, plus some of the old classic "brown glue" to boot. At the foot of a 2w resistor, it had darkened and went brittle already.
Primaries: 390u/200v -> Teapo LXK 680u/200v
Secondaries:
- 390u/50v -> Panasonic FR 560u/50v (woofer amp)
- 82u/63v -> Panasonic HFG 100u/50v (ditto, pi-filter output)
- 220u/35v -> Panasonic FR 270u/35v (tweeter amp)
- 220u/35v -> Rubycon YXF 47u/50v (ditto, pi-filter output)
They now have a good 2-3 seconds hold-up time, after i turn them off via the switch on the back
I didn't bother with the amp board (a handful of blue Su'scon general-purpose caps), i just wanted to reliable-ize the whole thing
First pic: post-fix faulty joint. I subsequently drenched the other three tinsel/voice coil joints, juuuuuuuuuust to make sure
Others: PSU. Some unknown-brand UC3842 knock-off, driving two IRF840's via a small toroidal transformer, in what seems to be a half-bridge configuration (going by the dark-red poly cap near one edge).
The ad said the bad woofer measured 0 ohms. Being the curious type, i measured both woofers myself, but my meter actually said "OL" on the bad one, ie. open-circuit.
The culprit turned out to be the broken joint where the woven tinsel lead (from the spade connectors) met up with the wire coming from the voice coil. a drop of flux, some "keyhole surgery" with the soldering iron, and a shovel of cyanoacrylate on top to secure the joint, and...
*Drumroll, please...* IT WORKS!...
Preliminary testing - terminals hooked up to my oscilloscope, slow sweep, "manually" wiggled the cone => wiggle of the trace on the scope screen
Oddly enough, my DMM couldn't get a steady ohm reading (wobbled between ~2 and ~12 ohms), but after i hooked it back up, it sounds and plays just fine
While they were still "on the way", some googling revealed "horror stories" about some PSU design fault (they have SMPS's inside) that lead to the "cooking" of the startup cap. Mine seem to have some newer revision, and the hot resistor and the startup cap are nowhere near each other
Amp board silkscreen say "2003", PSU board says 2009, plus a 2010 date stamp on the bottom.As long as i had them opened up, i decided to re-cap the PSU boards as well. All "FuhYin" caps, plus some of the old classic "brown glue" to boot. At the foot of a 2w resistor, it had darkened and went brittle already.
Primaries: 390u/200v -> Teapo LXK 680u/200v
Secondaries:
- 390u/50v -> Panasonic FR 560u/50v (woofer amp)
- 82u/63v -> Panasonic HFG 100u/50v (ditto, pi-filter output)
- 220u/35v -> Panasonic FR 270u/35v (tweeter amp)
- 220u/35v -> Rubycon YXF 47u/50v (ditto, pi-filter output)
They now have a good 2-3 seconds hold-up time, after i turn them off via the switch on the back
I didn't bother with the amp board (a handful of blue Su'scon general-purpose caps), i just wanted to reliable-ize the whole thing
First pic: post-fix faulty joint. I subsequently drenched the other three tinsel/voice coil joints, juuuuuuuuuust to make sure
Others: PSU. Some unknown-brand UC3842 knock-off, driving two IRF840's via a small toroidal transformer, in what seems to be a half-bridge configuration (going by the dark-red poly cap near one edge).
Attached Files
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