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#1 Wood

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Posted 18 November 2011 - 04:33 AM

Hi Forum,

One my K2's is suddenly starting to flash the signal indicator when no signal (after start-up around 5 to 10 min.). I measure an offset then on up to 0.7V on the ch1 speaker terminal and the 18" woofer displace a bit.

When further time is elapsed this issue stops again and act normal (after 30 to 45 min heating up?). Sometimes when the sleep circuit has been active, the 0.7V DC offset is gone with a little "puff" in woofer. By that I mean sleep function active for a few seconds then music on again and the DC offset seems to be gone. Could this be cause by a defective U105 or some other stuff?

Anybody know's if this is a know issue and the "work around" to it?

Regards
Flemming

#2 Wood

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Posted 21 November 2011 - 01:04 PM

QUOTE(Wood @ Nov 18 2011, 10:33 AM) View Post
Hi Forum,

One my K2's is suddenly starting to flash the signal indicator when no signal (after start-up around 5 to 10 min.). I measure an offset then on up to 0.7V on the ch1 speaker terminal and the 18" woofer displace a bit.

When further time is elapsed this issue stops again and act normal (after 30 to 45 min heating up?). Sometimes when the sleep circuit has been active, the 0.7V DC offset is gone with a little "puff" in woofer. By that I mean sleep function active for a few seconds then music on again and the DC offset seems to be gone. Could this be cause by a defective U105 or some other stuff?

Anybody know's if this is a know issue and the "work around" to it?

Regards
Flemming


Hello again,

I did further investigations and it seem that the error amplifiers (U105) sometimes is feeded with -120mV from somewhere. When this fault voltage is "resat" the K2 has zero on output. The difficulties with the below 1V on speaker terminals (now in both channels) is mainly when very low music is applied to the amp. Both U105 "flicker" and then when more level is added to the music, the dc error is adjusted!!!

My amp.  is using 160W from mains and generate a lot of heat. This gives an chassis temperature of 48 degrees Celcius (long term). Can the U105 due to heat, have reduced openloop amplification at that point and should I try to reduce the very high valued resistors feeding the pin8.

Can someone at Crown maybe comment on that?

Regards
Flemming

#3 joust

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Posted 15 May 2012 - 02:03 PM

It's a wild guess: Verify the (4) 100uF/25V in the power supply section. If the tolerance goes off, the lo-voltage rails may suffer and cause odd behaviors!