Denon AVR-X1000 MCU Shorted

[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 ?

[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]

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

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

[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

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.

[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

[budwich]

Re: Denon AVR-X1000 MCU Shorted

One question, where did you measure the +B / -B values that you reported? I am not sure I understand RJ's comment about the q5702... if I read the schematic right, it is dealing with the -B side of things and not +B... but then again, I did say I have only limited experience on this.

As for the differences in voltage, I would expect them to be close / very close. I don't believe its an "adjustment" (although could be) but more of something not right / happening.... almost like a diode / transistor difference somewhere... hence the previous question.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I measured B+ and B- at the collector of each output transistor.

I think RJ means Q5702 only conducts after C5708 is charged up (?) so that PRE B- line starts up AFTER the main B+/- rails are fully powered.

Still trying to find out why the rails are not exact inverse of each other...

RJ,

Yes the speaker relays click on. The amp stays on for up to a minute at most (usually much shorter) before clicking off with the infamous fast flashing power light. Going into diagnostic mode afterwards shows DC Protection was triggered.

There is no sound from the Tuner at all during that time.

I will measure at the inductors soon.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

can you also check the input powers at cn503... just for comparison sake at the "source". I still think your "negative observation" is a good clue.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I can't get to that connector during operation but you'll notice the schematic says both the Main B+/- run direct to the collectors of the output transistors with nothing in between (except for jumpers, maybe) so the readings should be identical.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

OK... I see the "soft start" function for the pre-amp that RJ is alluding to... :-)
maybe doing some simple resistance tests at each amp (strategic / accessible points) and compare the results to see if anything jumps out.

missed your post... sorry but I agree with your statement.

are you able to get at / check the wiring options around the -B area... there are some jumpers near that area along with something like the "#18" which seems like potentially some form of "fuse link" maybe.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I have here a similar, possibly the same main board from an AVR-E300. There are no #18 wires as stated in the schematic there are only traces bottom side of board which lead to the collectors of the output transistors for the negative rail. There are three jumpers used to get there all the same size from what I can tell. If one had no continuity I would not be reading anything at all the collectors.

I feel compelled to redo some of my voltage readings but cannot do so until later today.

Thanks for helping out, btw.

EDIT: I have tried using this main board in place of the one at issue but this board shuts off before the relays kick in IIRC.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

L5101-5501 all hover around 0.8v but go as low as 0.5 and as high as 1.1v on all channels.

The measurements were the same at the emitter resistors so I turned all pots down to minimum but the readings didn't change.

Also when the relays cut out and the unit goes to protection the readings at the emitter resistors jumps to positive rail voltage and begins to dissipate quickly but maybe that's normal ?

[R_J]

Re: Denon AVR-X1000 MCU Shorted

If ALL channel offset voltages (emitter resistor voltage) jump to positive, it must be something common to ALL channels. Are you sure you are not loosing the -B+ to the channels?
Do you have +12 volts and Pre-B getting to the preamp section?

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Are you sure you are not loosing the -B+ to the channels?

I don't know what you mean by that ?

Yes I have the 12v line and PRE B- getting to the preamp. And yes I agree it's common to all channels.

As stated earlier my B+ and B- rails are off by roughly the amount of the emitter voltage. Is that normal and/or ok ?

B+ = 57.5v
B- = -56.6v

[budwich]

Re: Denon AVR-X1000 MCU Shorted

have you checked the diodes in the connection jumper "pack" d5701 at the power input area. Perhaps the +B is shorted, resulted in a higher incoming +B causing a "differential".

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

That part is referring to the bridge rectifier making the B+ and B- rails. Could be leaking somewhat will give it a diode check.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

not sure whether you can... but in the DC detect / protect /activate circuit at the bottom of the main board diagram, there is a jumper (j5675)... which appears to bond the surrounds detection to the front detection. I am wondering if removing that jumper will allow you to determine if indeed both are having an issue or only one.... although you seem to indicate that you see DC on all outputs which then means it is further back in the circuitry.

sorry just throwing out ideas... I know from my crown endeavor, I was looking at the negative side of the amp because of high negative values but it turned out that the positive side had the issue is that design.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Ya colour me confused. It seems to be affecting all channels. What was the problem in the Crown amp ?