Denon AVR-X1000 MCU Shorted

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Had another look at this recently and the real problem here is more insidious than an amp problem.

In my previous post I was asking what the signals should look like before they go into the Preamp because I was suspecting there may be nothing there to be amplified.

Turns out the volume IC (IC891) is not passing anything on as its control lines to the cpu have gone high. What should be 33 ohm resistors on the SDA and SCL lines controlling the volume ic are in the mega ohms.

Due to the fact this board came with a shorted cpu it's likely the faults on the signal lines are numerous. I may try replacing those resistors but failing that I'd consider this one unrecoverable.

Thanks to RJ and budwich for indulging me.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I'm going to pull the amp board and go over it since there are a limited number of voltage checks I can do on the running amplifier section.

Incidentally, what should the channels look like as they leave the HDMI board (before amplification) ? If I put the meter on them I measure about 6v dc and basically no AC component. Seems strange and yet if I touch them with something I can hear the channel (with much noise) in my headphones...

[budwich]

Re: Denon AVR-X1000 MCU Shorted

some more "ramble" from me... :-)
IF you look at the amp stage, at Q5x05/06, the circuitry around them is "mirrored". Of course, I know nothing about things like "push / pull", class A, etc... but IF the rails are "significantly different", then the "mid point" of the design which appears to monitoring as the DC detection point is going to be "non zero". I don't see much adjustment in the area so it has to be somewhere else. I think this is your problem. The dc offset is greater than it should be.

[R_J]

Re: Denon AVR-X1000 MCU Shorted

Looks like the audio is selected by IC891 and fed to the amp

[budwich]

Re: Denon AVR-X1000 MCU Shorted

that's sounds like a preamp problem then.
I used a cd with 1khz test tone (actually it had choices), input that signal and then traced the input with a scope to see where it disappears or went noisy / dc offset or otherwise.
Crown doesn't shut down for DC as it was a DC300... :-) not nice for speakers though.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

You are right I do hear hum AND audio from each channel by touching those pins.

I redid the readings with D_Ground and they are the same. D_GROUND ohms out with chassis ground.

[R_J]

Re: Denon AVR-X1000 MCU Shorted

The headphone audio comes from the amp FL & FR amps, Can you access BN501 and touch pin 1 (FL) or pin 9 (FR) with your finger, there should be a buzz in the headphones on that channel if the amp is working.
What are you using for ground, as the chassis might not be at "A" ground.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Yes the DC_FRONT measures about 0.4v and the DC_SURROUND measures just under 0.6v. Neither is enough to turn on the protection if I'm reading the schematic correctly.

But in the way of an update,,, I removed the DC_PROT pin from the BN502 socket and the unit does indeed stay on. That tells me the protect circuit is working as intended.

I still get NO AUDIO from the headphone jack. Well, if I just about stop my heart from beating I can hear FAINT sound. In the end it likely is an amp problem after all lol.

Can you make out how the protect circuit works ? I though it would take at least 0.7v to turn on one of the transistors and pull the protect line to ground signalling a problem to the MCU but I must have something wrong.

BTW the protect line I pulled from the socket reads zero volts which is I think what it should read if there are no problems.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

OK... but I am not sure what "open" means with denon and this schematic. I was actually reading that as troubleshooting points to look for or use as opposed to NC (no connection). :-) If the jumper is not there, then based on the schematic, the front and surrounds dc detect / protect lines are not linked and therefore either one can be checked / watched independent of the other. You can then do some resistance measurements from those points in the protection circuit back toward the amp / preamp at "select" areas and compare the results... one would expect similar results for the front and similar ones for the surrounds... the front and surrounds may not look similar as the sections might have a slightly different setup.

Further, since the two protect lines are seperated, you previously mentioned some of the voltage readings that you were monitoring and jumping around or otherwise... which line were you monitoring? Did you watch / check both?

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

It is starting to look like it is in the protection circuit, those are smd transistors, so maybe a poor connection, maybe try some cooling or heat in that section of the board

Going to try to get some heat there but there in a hard spot and on the bottom of the board. Looking like I'll be pulling the board soon.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

You might try my suggestion about the jumper in the protection circuit which then allows you to isolate the front from the surround in terms of protection. Then check the voltages at those two "halves" to see if you notice a difference in the detection operation. Might help.

A good idea but if you're talking about J5675 it's marked as "Open". I'd either have to remove components or cut a trace or two.

The other thing that you can look at is doing resistance measurements along the protection line and comparing the result at each channels to see if anything is obviously different. You aren't necessarily looking for shorts to ground / opens although those would likely be of interest but just a plain obvious difference. You are dealing with DC issues so a metered resistance check / snoop will likely be of use.

Will definitely do some of that before tearing the amp apart again.

[R_J]

Re: Denon AVR-X1000 MCU Shorted

It is starting to look like it is in the protection circuit, those are smd transistors, so maybe a poor connection, maybe try some cooling or heat in that section of the board

[budwich]

Re: Denon AVR-X1000 MCU Shorted

You might try my suggestion about the jumper in the protection circuit which then allows you to isolate the front from the surround in terms of protection. Then check the voltages at those two "halves" to see if you notice a difference in the detection operation. Might help.

The other thing that you can look at is doing resistance measurements along the protection line and comparing the result at each channels to see if anything is obviously different. You aren't necessarily looking for shorts to ground / opens although those would likely be of interest but just a plain obvious difference. You are dealing with DC issues so a metered resistance check / snoop will likely be of use.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

I was thinking there are three possible scenarios here, four if we count yours.

1) There is a leaking transistor in the DC PROTECTION circuit pulling the 3.3v to ground

2) The SWM_3.3v line (used to power the protection circuits) is faulty and being pulled down for another reason.

3) MCU problem

My head still tells me that any difference in B+ and B- will show up as DC offset at the speaker terminals but RJ rules that out.

Next step is I guess to pull the amp section out.

[budwich]

Re: Denon AVR-X1000 MCU Shorted

I would check the transistor that I mentioned at the start to ensure that it is good as it is "setting up" the preamp just ensure that it is indeed functional.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Have you checked the voltage on BN502 pin5 to see if the DC_PROT line is actually changing? Maybe it is not the amp that is at fault but the protection circuit it self, or the micro giving a false protect error.
It must be because you have a avre300 board in the avrx1000. I see there are version option resistors that are different between the models for IC761

I don't have the AVR-E300 board in, only tried it once to see if that amp board would stay on without giving a fault. It did not.

The DC PROT line is in fact changing. Starts out at about 3.2v and bounces around a bit then starts going into free fall and the protection kicks in as it passes through 0.7v (enough to turn on a transistor ?)

What's weird though is if I measure R5x31 which drives the protect circuit I do not see the voltage change. DC_FRONT measures about 0.33v and DC_SURROUND measures about 0.56v. When the protect circuit kicks in those voltages change to 0.7v

Here is the other section of the protect circuit.

[R_J]

Re: Denon AVR-X1000 MCU Shorted

Have you checked the voltage on BN502 pin5 to see if the DC_PROT line is actually changing? Maybe it is not the amp that is at fault but the protection circuit it self, or the micro giving a false protect error.
It must be because you have a avre300 board in the avrx1000. I see there are version option resistors that are different between the models for IC761

[budwich]

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 ?

It had one channel with high distortion which had some outputs transistors in trouble but also a high DC level seen at the input stage / preamp area. Eventually I found a transistor associated with the positive side not functional.
Once replaced, everything became normal. As I said, I only have limited experience but was interested in your effort and hoped to help and learn as I have two denons(3805 4310) one of which has a level issue where loudness / volume seems to slowly drop thru the day. So its kind of "follow along" road for me with hope / learning. Sorry, if I have not helped... I will just monitor and wish you luck.

[mmartell]

Re: Denon AVR-X1000 MCU Shorted

Yes my mistake, was thinking of how you set to fully counter-clockwise before making idle-current adjustment (at least for receivers I've done that for)

The thing is the amp isn't in Protection until the detected by the MCU, which is up to one minute at times. Still no output to the speakers, at least not from the tuner. Shouldn't there be something ?

[R_J]

Re: Denon AVR-X1000 MCU Shorted

If the amp is in protection you can't set the offset pots.