Harman Kardon AVR5 starts, clicks, shuts off

[Qaziz]

Hey everyone,

A friend of mine recently asked me to take a look at her AVR5. She doesn't recall a specific event where it stopped working.

Situation description:

The AVR5 will successfully power on to standby mode when the main power switch is pressed, or at least the power indicator (LED behind the system power control button) will turn amber; this is the normal standby mode color according to the service manual. When the system power control button is pressed, the LED switches to red (protect mode), there is a buzzing noise (I think this is a normal startup sound), and then a clicking noise which I think is localized around the two large, central capacitors, then the system shuts off again. The LED will turn green (operational mode) for a fraction of a second before it shuts off. It then remains red until I cycle the main power switch.

What I've done:

First, I unplugged all loads from the system to ensure there wasn't an external short that was causing it to enter protect mode. Then, I opened up the case and removed all five fuses (verified this was all of them with the service manual) and tested them both with my ear and then with a multimeter, where they all showed minimal resistance. I then checked all of the MOLEX-style power connectors and re-seated them. Finally, I inspected the board for bloated/leaking capacitors or burn marks on other components. No dice.

Photographs of the board and the capacitors that I think the clicking sound is coming from: http://imgur.com/a/caUTU

I also recorded a video. It's quiet, and there's a bunch of interference in the audio (coming from the AVR5 I guess?), but you can hear the clicking sound I mentioned pretty distinctly. I cycle the system power control multiple times in the video: https://youtu.be/ySXJoQSLVms

Oh, and that weird brown stuff around the base of some of the capacitors is some kind of glue I think. It's on a lot of components, and not just capacitors.

Thanks for any help or insight you can provide! I'm pretty new to all of this.

[999999999]

Re: Harman Kardon AVR5 starts, clicks, shuts off

On your second (middle) picture, below the large caps and to the right is what looks like a relay, next to the small transformer. Maybe it's a film capacitor, check the markings on the side if visible or # of pins as a relay will have 3 or more and film cap usually only 2. If a relay, that should be what is clicking as a protection circuit because something is shorting out, so it's just a symptom, not the problem.

Most likely it's one of the transistors on the large rear heatsink or one immediately before it in the circuit. There are other possible causes but less likely and possibly beyond the scope of a forum post unless you find some specific clue probing the circuit live, after looking for burnt components, bulging capacitors, solder or circuit board cracks, etc.

Live probing AC mains powered equipment is not something I would normally advise to someone who didn't recognize a relay, but basically you are looking at clean power and tracing the audio signal, which shouldn't be there if no audio is supposed to be playing. Audio path transistors shouldn't conduct when there is no audio.

You can also unplug those 4 daughterboards to rule them out, then the mainboard is power and (best guess) all power amp on the rear board parallel to the heatsink.

[Qaziz]

Re: Harman Kardon AVR5 starts, clicks, shuts off

Thank you! The board is sort of difficult to work with - it seems like the daughter boards are actually soldered on. I'm not feeling super optimistic about it, but I really appreciate the detail, and I've learned something just trying to figure this out.

I'll let you know if there are any miracles.

[tibimakai]

Re: Harman Kardon AVR5 starts, clicks, shuts off

I agree with 999.. I would suspect the final transistors mounted on the big heat sink. I would measure all of them with a diode tester. No power while you do this, of course. Usually two are shorted next to each other. Cut there legs and the receiver, should turn on.