Denon AVR-2802

[Diver300]

I'm trying to fix a Denon AVR-2802 with a bit of an odd problem.

The Denon AVR-2802 is a bit of a strange mix of technologies. On the one hand it is digitally controlled, uses 0402 surface mount resistors and has digital optical inputs available, but on the other hand some of the boards are phenolic resin, single sided with numerous wire links and the power supply is linear with multiple different windings for different voltages, including a high voltage output to run the electroluminescent display

The amplifier will work when turned on, but as soon there is any change to which input is in use, or which of the speakers is in use, there is no sound.

I have traced the signal and found this:-

The selector is a multiway analog switch, presumably also controlled by the microcontroller. The selector works, and the phono input signal is always transferred through to the input of the TC9459N when phono is selected using the function knob on the front.

When the unit is first turns on and is working, the turning the volume knob results in the microcontroller sending clock, data and then strobe signals with each click of the volume knob to the TC9459N which works fine and sends out the signal to the amplifier, and sound can be heard.

After the selector or the speaker switches have been operated, there is no output from the TC9459N, but there is also never any clock data or strobe signals from the microcontroller to the TC9459N. The display on the front panel still shows the gain changing when I try to change the volume, but obviously nothing gets through the TC9459N as it remains on zero volume.

Has anyone got any suggestions where to look next?

 

[rjenkinsgb]

Power supply glitches? I'd check for noise around the MCU.

 

[Diver300]

I couldn't find any glitches around the microcontroller. I added a 100 μF tantalum to the 5 V power rail for the microcontroller and a 10 nF as close as I could, but there's no change to the behaviour. The power rail doesn't fluctuate.

The microcontroller is run from a small mains transformer and it says on whenever the unit is plugged in. There is also a 5.3 mF, 6 V capacitor that keeps the microcontroller running when the mains is disconnected. The instructions say it should stay keep the settings for a week if disconnected from the mains. I checked the voltage and it decayed less than half a volt in an hour. The 5.3 mF capacitor is yellow, while all the other electrolytic capacitors are black. I guess that it's an early supercapacitor.

When the volume control is operated, there is data sent to the digital potentiometer. Once a selector is operated, that no longer happens.

There is also data sent each time a selector is operated, but it appears to be a different format. That data will be sent on every press, even though the volume data isn't present after the first time a selector is operated.

Tomorrow I will try to look at what is being sent in each case.

 

[rjenkinsgb]

Have you tried the hard reset? (first two lower buttons held in while powering on)?

The block diagram early in the manual shows a clock signal to the DSP section from the DIR module, whatever that is. Are all the clock signals OK after the fault occurs?

(I was looking at this manual:
https://www.manualslib.com/manual/1381370/Denon-Avr-2802.html )

 

[Diver300]

I had tried the hard reset, but it made no difference. The display did flash as it's supposed to when doing the reset.

I don't think that I've really be using the digital signal parts so far so I don't think that the signal from the DIR to the DSP matters. I may go and see if I can find it. The service manual has quite a lot of good information but there are only some of the schematics in there. Each one has been expanded out into each corner, as if it will be printed on A4 sheets of paper. There are only 3 of the 12 schematics.

I realise that I may have been doing the wrong thing feeding the phono input, as I've only just learned that the phono input is equalised for a record player. I will try with the CD input.

 

[Diver300]

The only input that works is the phono one. I suppose that gives me something else to trace.

 

[rjenkinsgb]

Does it store the last used input?
What happens if you select CD or tape or whatever, then power off and back on again?

 

[Diver300]

Does it store the last used input?
What happens if you select CD or tape or whatever, then power off and back on again?

I tried that. No sound. I have yet to trace how far the signal is going.

 

[Diver300]

I've just used a logic analyser to look at the signals sent to the volume control. When the volume control responds, the signals are exactly what I would expect according to the data sheet of the TC9459, so 24 bits of data followed, clocked in by a clock signal, followed by a strobe pulse.

The clock rate isn't consistent but I guess that's just the processor doing something else.

That is followed by more data and 32 clock pulses, and a strobe to something else, so I assume that is data being sent to the signal selectors which share the same clock and data lines but not the strobe line. Edit:- It's actually to another digital potentiometer, the one for the direct analogue output.

The data after the strobe does not change when the volume is changed.

When the input is selected, the volume signal is sent with the minimum volume setting, followed by three frames of 32 bytes each:-

This is sometimes followed by another set of data about 0.7 seconds later.

So the problem is that when the input is changed, the volume reverts to minimum, and then new volume levels are never sent to the digital potentiometer, even though the display on the front of the amplifier shows the volume level as changing.

 

[Nigel Goodwin]

Does the volume change smoothly?, a VERY common issue (which causes all kinds of weird effects) is a duff and noisy rotary encoder, across all makes of units.

 

[Diver300]

Does the volume change smoothly?, a VERY common issue (which causes all kinds of weird effects) is a duff and noisy rotary encoder, across all makes of units.

When the volume works, it changes perfectly smoothly. The volume reading also changes smoothly.

 

[drtechno]

I've just used a logic analyser to look at the signals sent to the volume control. When the volume control responds, the signals are exactly what I would expect according to the data sheet of the TC9459, so 24 bits of data followed, clocked in by a clock signal, followed by a strobe pulse.
View attachment 145232

The clock rate isn't consistent but I guess that's just the processor doing something else.

That is followed by more data and 32 clock pulses, and a strobe to something else, so I assume that is data being sent to the signal selectors which share the same clock and data lines but not the strobe line. Edit:- It's actually to another digital potentiometer, the one for the direct analogue output.

The data after the strobe does not change when the volume is changed.

When the input is selected, the volume signal is sent with the minimum volume setting, followed by three frames of 32 bytes each:-View attachment 145233

This is sometimes followed by another set of data about 0.7 seconds later.

So the problem is that when the input is changed, the volume reverts to minimum, and then new volume levels are never sent to the digital potentiometer, even though the display on the front of the amplifier shows the volume level as changing.

Then you will have to look where its malfunctioning. I would check to see if the soft mute circuit pin off the processor is really changing or not. Because it sounds like the volume control is working, but the processor muting circuit isn't which could be just a buffer to the soft mute pin.


Attached is a service manual I found off the internet so you are not trying to work in the dark with this.

 

[Diver300]

Then you will have to look where its malfunctioning. I would check to see if the soft mute circuit pin off the processor is really changing or not. Because it sounds like the volume control is working, but the processor muting circuit isn't which could be just a buffer to the soft mute pin.


Attached is a service manual I found off the internet so you are not trying to work in the dark with this.

Thank you for that. I will go and find the soft mute pin.

The service manual is the one that rjenkinsgb post a link to. There are only three of the 12 circuit diagrams at the end.

I think that the signal is getting lost somewhere in the Audio/DSP board, which is item 5-1 on page 56.

The phono signal enters on the back of board 2.1, transfers through the control unit (board 3.1) to the Audio DSP board, then through the control board again, to board 2.1 for a second time, and then onto the connect unit (board 2.2) to the power amplifier. It's all a bit complicated.