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Old 09-29-2013, 07:38 PM   #27
Khron
Badcaps Veteran
 
Join Date: Sep 2006
City & State: Valkeakoski
My Country: Finland
Line Voltage: 230VAC 50Hz
I'm a: Professional Tech
Posts: 1,113
Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I just (finally) received my 2nd pair of M1 Mk.2's last week - these ones wouldn't switch on.

Sure enough, "first generation" power supply, with the start-up cap right up against the dropper resistors coming from the +320v rail. Upon desoldering, just for kicks, i measured it. Said 220u/35v on the sleeve; the cap range on my multimeter said 69uf :roll:

I decided i'd go "all out", and used a Panasonic FR 560u/50v as a replacement 2.6A ripple / 10k hours, vs. 640mA / 2k hours on the original

I chose a more "elegant" route for the actual replacing though: desoldered the 10nF ceramic cap next to the UC3844, used its holes for the Panny, and slipped the ceramic back in underneith the board, straight on the Vcc/Gnd pins of the chip That's the area they re-located the start-up cap on the later revisions anyway (on my first pair).

For what it's worth, the coating on the current-sense resistor was starting to "crack", but no flaking or disintegration going on (just yet), "only" some board discoloration right underneith it. I added some fresh solder to its pins/pads, looked a bit "dried out" to me...

Either way, stay tuned for pics tomorrow, when i "do up" the second one (it's 3:35am here, so... )
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