Denon AVR-X1000 MCU Shorted

[R_J]

Re: Denon AVR-X1000 MCU Shorted

Q5702 is just a soft start switch for the preamp section B+, it is setup to delay the B+ to the preamp section until after the main output is powered.
Do the speaker output relays click in?
If you are measuring voltage at the speaker terminals, that would suggest that all the speaker protection relays are energized (so the amp is NOT in protection) But it could also just be phantom voltage and not the actual offset voltage.
I would check the actual offset voltage on L5101 ~ L5501 it could be that one output section is bad

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I think you're talking about Q5702 ? I don't know what it's purpose is but I would think if it was meant to bleed off voltage there would be a resistor to ground and not a cap ?

But yes if it's faulty I suppose it could destabilize the negative rail.

And yes I was wondering if the voltage for the positive and negative rails should be identical, or if there is usually some mechanism to adjust them as such.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

I was just poking around with interest. don't know anything about receivers much more than recent efforts on a crown and onkyo, but I do have a couple of denons, hence my interest. I was looking at page 96 of the service manual, at where the -B is delivered to the main board. It appears to be going thru some transistor to get into the rest of the board. Is it possible that "switch transistor" has an issue and is leaking after the fact voltage into board even with shutdown. Related, I guess depending on the type of amplifier design, perhaps the +B and -B should be closer in value otherwise, there maybe some form of DC "left hanging around"... :-)
Of course, I know nothing but just thought I would bounce some thoughts for you to ponder.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Still -35.1v after sitting unplugged overnight. How is this voltage designed to dissipate ?

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

This might be unrelated but after power down and unplugging the positive rail goes to zero but the negative rail only falls down to -35.4v and stays there. Is there a bleed resistor for the negative rail I should check ?

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Came across an HDMI board from the sister unit (AVR-E300) and transplanted the MCU into the non-working board.

Unit boots up and all buttons and knobs function but the unit goes into DC Protect mode after varying amounts of time but within a minute for sure.
There is no sound produced at any time, and nothing from the headphone jack either. None of the output transistors are shorted.

There is a very small voltage (4mv) at the bias resistor pair but there is a DC offset at all five speaker terminals of 300-500 milivolts!

B+ and B- are at 57.3v and -56.7v and the 12v is steady.

How to troubleshoot ?

[mmartell]

The MCU gets roasting hot when unit it plugged in, more so than surrounding components I'm pretty sure it's shorted.

I can buy the MCU from Digikey but the it looks like it would need to be flashed with firmware and I don't have the jig for that.

Can't find a parts unit to harvest from so that's out.

Suggestions or do you think the HDMI card may have other shorted IC's from whatever killed the MCU and the unit should be parts-binned ?