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Old 12th October 2005, 08:24 PM   #1
xinix is offline xinix  Netherlands
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Default Harman Kardon HK6600

Hi Guys (and Gals of course). I'm trying to fix a Harman Kardon HK6600 amp. (see circuit diagram: http://manuals.harman.com/hk/Service...K6600%20sm.pdf ) It has a 4 V DCoffset on one of the outputs. I've replaced Q404,406,408,410 and 446 allready, and measured all releveant resistors, but no cause yet. Any ideas?

thanx, Philip
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Old 12th October 2005, 08:33 PM   #2
Netlist is offline Netlist  Belgium
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Does trimming VR402 improve things?

/Hugo
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Old 13th October 2005, 02:45 AM   #3
xinix is offline xinix  Netherlands
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Default HK6600

Hi Hugo, yes, slightly, but I can't get less than appr. 3V DC.
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Old 14th October 2005, 12:12 AM   #4
anatech is offline anatech  Canada
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Hi Philip,
The first thing to do is see if the diff pair is attempting to correct the offset. Measure the E-B junctions to see if any are reverse biased and make sure the CCS is running. Measure voltage drops across R418, R412 and R414 to show current flow.
Q446 is a regulator, so you can measure the voltage drops. The DC offset control has an effect so the stage may be working fine.
Where ever you see a resistor on an emitter, measure the voltage to confirm current flow. Also measure E-B drops. You can do this at reduced voltage, be careful not to short anything.
Beware the no burn resistors. They can look fine but be open. Sometimes it's just as easy to discharge the supplies and measure the darn things.

-Chris
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Old 15th October 2005, 02:36 AM   #5
dudu is offline dudu  Israel
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Default Hk6600

HI
I'm sorry about my bed English ,but i'll try .
Becouse u have the same faults on both two channels . U have to looking for any problem on common circuit - May be "Mute-protector" circuit.

To be sure that the power amp' is well .u have to insulating the circuit and check it with double power supply.

Dudu
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Old 16th October 2005, 07:32 AM   #6
xinix is offline xinix  Netherlands
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HI Chris & Dudu,

thanx for your replies. First, the problem is in the right channel only. Second: during powerup, there is no DC due to the muting circuitvia Q418.

I will try your suggestions Chris, first thing monday. By the way, what is CCS?

nice weekend everybody,

Philip
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Old 16th October 2005, 04:02 PM   #7
anatech is offline anatech  Canada
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Hi Philip,
Sorry, a CCS is a constant current source. It allows wide variations of collector voltage (in this case) while sourcing or sinking the same amount of current. They are most commonly used for tail current on a differential pair. Q408 / Q410 make up the "CCS" in this example.

Q418 is a voltage regulator, around 14.4 VDC. There may be a small delay formed by the 22K resistor and 47uF cap. Maybe around one second. Probably less as one time constant is beyond 14.4 V, 0.63 X the supply voltage.

-Chris
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