The multimeter reads + 4.5vDC on right speaker Channel - 4.5vDC on left speaker Channel.
it should read 10mv in 8 ohm and 60mv in 4ohm....
I have compared left channel with right channel with ohm meter they read exactly the same...
i have changed capacitors with incorrect value
leaky transistor maby??
anny ide whats wrong ? 🙂
http://manuals.harman.com/hk/Service Manual/HK6600 sm.pdf
it should read 10mv in 8 ohm and 60mv in 4ohm....
I have compared left channel with right channel with ohm meter they read exactly the same...
i have changed capacitors with incorrect value
leaky transistor maby??
anny ide whats wrong ? 🙂
http://manuals.harman.com/hk/Service Manual/HK6600 sm.pdf
It should read zero for all conditions but has a tolerance. Altering the 4/8 ohm selector alters the supply voltage and that can have the effect of slightly shifting the operating point of the circuit.
All you are measuring is the DC voltage at the output of the amplifier. If the amp is working OK then just measure the DC voltage across the speaker terminals. Should be zero,
Nope, just for reference .
Are you sure about the +4.5v on the right and -4.5v on the left, have you not reversed the touchpoints of your DMM ?
Are you sure about the +4.5v on the right and -4.5v on the left, have you not reversed the touchpoints of your DMM ?
I'm sure 🙂 it's reads good for a few seconds when I start the amplifier then it goes up to 4.5v. I was looking for the differential pair transistors ore some transistors that's controls the voltage to the amp but no success yet
Have you checked all the supplies are correct? That is the first rule of fault finding.
You have have critical supply points on the diagram @huggygood posted.
(Diagram doesn't show values for VCC/-VEE but would expect them to be around +/-50 volts)
1/ VCC
2/ -VEE
3/ Voltage on output side of R462 (should be similar to VCC)
4/ Voltage on output side of R464 (should be similar to -VEE_
5/ Voltage on emitter of Q446 (should be approx -15 v)
It is odd for both channels to have similar faults.
You have have critical supply points on the diagram @huggygood posted.
(Diagram doesn't show values for VCC/-VEE but would expect them to be around +/-50 volts)
1/ VCC
2/ -VEE
3/ Voltage on output side of R462 (should be similar to VCC)
4/ Voltage on output side of R464 (should be similar to -VEE_
5/ Voltage on emitter of Q446 (should be approx -15 v)
It is odd for both channels to have similar faults.
Are you certain the black ground meter probe is actually connected to ground?
Use the ground post on the back of the amplifier.
Post a photo of how you are connecting the DVM to measure the output DC voltage.
Use the ground post on the back of the amplifier.
Post a photo of how you are connecting the DVM to measure the output DC voltage.
That sounds reasonable. Emitter of Q446 should be negative 14.5... typo 🙂
Were R462 voltages OK? Looks like the rails are -/+46 volts so you should have plus 46 on each side of R462.
Strange to have a 'low' DC offset fault as normally failures are catastrophic and simple send the output to one rail or the other.
Has the amp a hidden history? Recent acquisition etc 😉 Has it been worked on by persons unknown?
This amp is unusual in that it has flat gain to DC, and only the input has AC coupling.
It's good that it's misbehaving consistently--- it will be easier to troubleshoot. 😉
Does the output respond to VR402? Does it "feel" noisy? What adjustment range does it offer?
I suggest reporting voltages at amp output and bases of Q404 and Q406, with respect to ground. Report negative voltages as signed voltages.
It's good that it's misbehaving consistently--- it will be easier to troubleshoot. 😉
Does the output respond to VR402? Does it "feel" noisy? What adjustment range does it offer?
I suggest reporting voltages at amp output and bases of Q404 and Q406, with respect to ground. Report negative voltages as signed voltages.
Agree with others above, try adjusting VR402. Note the range of output voltage when you set the wiper at min/max points. The weird thing to me is how one is positive offset and one is negative. I'd expect the wiper to open, and then VR402 would go to max resistance, and both channels would go to 4.2. And the wiper could be intermittent which would explain why one channel is ok sometimes.
Potentiometers are not reliable in the long term. The wiper oxidizes, loses contact after a decade or four. Setting DC output with a pot is a major design defect. If adjusting VR402 brings the output tnto spec, +-10 mv to speaker ground, definitely replace the pot with a fixed resistor of the same value.