Harman Kardon AVR 171S - standby led lights up, does not turn on

[madsox]

Greetings!

Thank you in advance for your understanding, I am writing to you through a translator.

A Harman Kardon AVR171S amplifier was given.

The history of the machine is as follows:
It was faulty when I bought it, I want to fix it.
I replaced the HDMI switch and one of the DAC ICs in it.
After that it worked without a problem.

I watched a movie using the amplifier, and at the end the amplifier got really hot.
The cooling was faulty, I will fix this later.
I switched it to standby mode, waited for it to cool down, then took it apart to fix the cooling.

After that, the machine did not turn on.
The standby LED lights up orange.
It does not respond to the power button or remote control.
Pressing the surround mode button for 5 seconds does not reset.

The power supply only supplies standby 5V.
The STM microcontroller starts, it is not in reset due to low supply voltage (by IC1503), the correct 3,3V is present.

By visual inspection, there are no faulty, burnt parts or humped capacitors.

On another forum, I was advised to check the voltage value of the POWER_DOWN pin, because the PC95 optocoupler may be faulty.

I measured at the input of the optocoupler (PC95):
AC 0,75-0,82V; DC 0,38-0,45V

On pin 15 (POWER_DOWN) of connector BN65:
AC 2,47V; DC 0,56V

I think here that the DC 0,56V is low for the processor, that's why it won't turn on.

Voltages measured on some legs of the controller:
1. PROTECT: DC 3,32V
2. POWER_FAIL: DC 3,32V
3. POWER_DOWN: DC 1,89V

Do you think the optocoupler is faulty and that is why the device does not turn on?
Is it because the amplifier does not turn on because it does not detect the correct input mains voltage?

Does anyone have an idea where I should look for the error?

(Unfortunately, I don't have an oscilloscope, but if you ask for a measurement, I will do it with my multimeter and report back with the results.)

I trust your experience,
I really want to use the amplifier.

I have attached the service manual.

Thank you, Thomas

[stj]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

how did you fix the cooling, did you replace a 3wire fan?

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

The temperature sensor was mounted on the power supply (on the 12V voltage stabilizer) instead of the heat sink of the amplifier transistors.

Someone tried to fix the amplifier before me, I wasn't the first.

If that doesn't help, I'll install a fan controller (https://www.aliexpress.com/item/1005004752252602.html) for proper cooling.
They have worked great for my computers, it will be good here too if the built-in controller is faulty...

[petehall347]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

does it have a self test mode ? proceed with caution if it has

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

I did not find any reference in the service manual or user manual to any self-test function.

Thank you.

[stj]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

does it have a 3 wire fan?

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

No, the amplifier has 2 wired fans.
On the ali' control panel, the fan pwm leg is connected with the input connector pwm pin, it is not used to speed control.

Or what are you thinking?

[barg8]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

Hello everyone

I have the same problem with my AVR 151s
You successfully solved the problem ?

[barg8]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

You successfully solved the problem ?

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

Hello.

Unfortunately, I didn't make it any further, it's been standing for a year.

I found a good solution for a Focusrite sound card, but the topic seems to have stopped.

I tried to ask in other places, without success; the questions stopped just like that, no matter how much I brought them up again and again.

If you manage to get any information, I would be very grateful if you could pass it on to me.

...

Although, now I'm at home sick, I also got an oscilloscope.
I'll dig into a few and see if I can find anything.

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

Well.
I measured the digital PCB.
And it's the worst.

The microcontroller have shorted.
How to replace that, I really don't have idea.
Okay, the IC is available, but the program. . .

[barg8]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

How to check this short circuit and in what system it occurs

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

Where can you short circuit? Anywhere.
Any capacitor, any resistor, IC or transistor can go into short circuit.

I found it by unsoldering the components one by one, measuring, unsoldering, measuring... in the end there was nothing between the +3.3VC and the GND line, only the controller.

Of course, it is worth searching for each part and island.

There is the injection method, but I haven't tried it yet.
With this method, the short-circuited component can be heated within the circuit,
and it can be determined from the rate of alcohol evaporation or found with a thermal camera.

[barg8]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

I check all my pcb and i dont have short circuit 3,3V to GND :płacz:

[madsox]

Re: Harman Kardon AVR 171S - standby led lights up, does not turn on

You have to measure, even with an oscilloscope, and look for oddities and anomalies.

Unfortunately, I can't say more, but maybe another forum member can give me an idea.

I change the e.capacitors first, they are the first ones that generally break down.
If it doesn't help, I'm looking for a heating part.
If there is, and it is suspected to be faulty, I will replace it without a thinking.
If it doesn't help, the scope and thinking with my hands on the wiring diagram will come.

I hope you have more success than I have so far.

I contacted Harman Kardon, they referred me to a service center, who said it was beyond repair.
I don't care about that.
Don't let it become garbage just because of its single microcontroller program unavailable...

[TunedPort]

I also have a Harman Kardon AVR2650 STANDBY LIGHT TURNS ON , but occasionally will not turn on .