X-Series - HX165.4 No Output, All Channels

[Piasa]

The Power Supply is good, +/- 40V at both rails.


The Supply for the PreAmp +/- 16V was bad, burnt trough Z-Diode but is good now.

I´m not sure with the Q5, could be a NPN Transistor or some Rectifier Diode in SOT23.



The input signal reaches the amplifier stage but I have no output.


The 38V are at the Gates of the Output FETs and the 39V at the Sources.


Now I´m a little lost where to start.


The Semiconductors are good, no shorts.


I don´t rly understand the function of the (IC15) 5532 Dual OPAMP, why is it supplied by AC?

 

[Perry Babin]

I don't know your amp but the configuration may be similar to the attached diagram.

Do you have the bias voltage?

 

[Piasa]

Thank you for the schematic, i underestimated the bias a lot.
I traced the basis back and found a defect Transistor, measured it wrong (I thought a resistor in parallel pulled the value down to 90 Ohm)

Then it went into protect, it wants both preamplifier boards in curcuit to power up. 1,13A with 13,5V.

I will try again now, thank you very much.

 

[Piasa]

The Amplifier has a Bias of -6,64V and +6,98 at all channels. Is that the Value that you are meaning?
I measured that Voltage from Input ground to the pins of H1 to H4.

 

[Perry Babin]

I'm not sure of the specific voltage but if you had audio up to that point, you needed to be sure that that last (bias) supply was switching on.

 

[Piasa]

I didn´t change the BIAS potentiometer settings. It was never opened before.

Just a new Z-Diode, 2 new Transistors and it works again.
Will give it some stress tomorrow and see if it keeps running.
The schematic helped me a lot, thank you perry!

 

[Perry Babin]

To clarify, I was referring to the ± bias supply, not the idle current bias setting.The bias setting shouldn't need to be adjusted if you didn't replace anything in the circuit beyond the bias pot.

 

[Piasa]

I found another fault the channels are all fine now in Stereo-Mode.

But when I switch into Mono-Mode Channel 1+2 are working fine but channel 3+4 just breaks down.

Could that be a bad OPamp or a defect Switch? And how is that Mono realised?

 

[Piasa]

I see in the schematic that you posted the OPamp U5-B that is putting Input 1 and 2 togehter, could that be it?

 

[Perry Babin]

Connect channels 3 and 4 normally and try working the switches back and forth to see if either or both channels cut off and which switch causes them to become intermittent.

 

[Piasa]

The Mono Switch, Channel 3 and 4 Signal way just dies when I press it. Stereo mode is working fine, so I think that the OPamp for the Monomode is down.


I will need to check if the switch is halfdefective or the Opamp.

 

[Perry Babin]

When in mono mode, do any other switches appear to be intermittent?

 

[Piasa]

Nothing striking, I have for both channels the same settings. The Filters and so on are in Off position.

 

[Perry Babin]

You'll have to follow the signals through the amp to see where they are lost.