Denon DRA-F107 sound output only on one channel

[roli]

Hi!
I recently got my hands on a used Denon DRA-F107DAB receiver/amplifier. For the most part it is working perfectly fine, except for audio output on the right speaker channel. The left channel works perfectly fine, but the right one is dead. However headphone output for example works perfectly fine and in stereo.

Obviously I checked the settings first, and those look fine. There doesn't seem to be any exploded components or anything visually wrong. I've attached the picture of the whole thing, and a separate picture of the amplifier board - which to me seems to be the most likely candidate. When it is placed in system you can see it next to the blue relay, which would be my second suspect. Although when switching inputs I can hear it clicking and I don't think there are any other relays on the board.

Here is a link to the service manual that i found: https://www.manualslib.com/manual/1500285/Denon-Dra-F107.html

For the most part I would suspect the audio amplifier board, but I am not sure what exactly on there. From what I can see on the schematic all of the active components are shared between the two channels - though all you have are two op-amps and the main amplifier IC (located under a heat sink on the back). So I would assume that that all of the power regulation is ok. My other suspect would be the blue relay. From what I can see it is the last stop for the audio before going to the connectors.

I am not really familiar with audio equipment though, so I am not sure what is likely to fail on similar stuff and what should I check first. That is why I am here. Any ideas on what would be the best place to start poking around?

[Swake]

Poking around... you'd have to poke around with something and that would be at least a multimeter. Do you have one at hand and do you understand how to use it?

If yes, you can try following the audio path and find out up the where there is some audio signal. I would first reverse the path and work my way from the speaker connectors backwards till I find a signal.

That blue relay might certainly be faulty, you would be able to measure something on one side but not the other.
Is there something on the output of that audio amplifier board? If not check if there is something on the input side.

On the block diagram on page 55 of the service manual you'll find a 'mute' box just before the amplifier, whatever is in there might be faulty too and would not impact the headphones as it is just behind

[roli]

Yes, I do have a multimeter and a scope. I even know how to use it  . So tools wise I am all good.

The main issue is with the very compact nature of this thing, so getting to the audio amp board while it is in the system is impossible - since it's basically sandwiched right next to the mains input board. So I guess I need to solder some wires or try and use jumpers and move the board out. Luckily it's a standard header connector.

Good advice. I will try going backwards and see if I can find something.

[roli]

So, I finally had time to poke around, and this is getting "fun".

So, my tracing has revealed that the right signal doesn't even reach the amp board. So, I went back to NJM2068 - IC24 on the main board (see page 80 of the service manual)... signal wasn't there either. I checked back on the C248 (which is the first component that the signal touches after leaving the main "switch IC")... not there either.

Which means that the signal isn't even leaving IC21... Now IC21 is a M61531FP... which looks to be like the main switcher chip actually doing things. What I don't get is... if this chip was the problem... how do the headphones work? The schematic is confusing me and I am having trouble actually finding the headphones output at all on there. So not sure if this is the problem chip, or is something before there doing this. Of course the chip is a dense SMD IC, so measuring things with the scope will be a challenge.

Any ideas on what I should look at next?

[Swake]

A/
The headphones output on the M61531 are on pins 47 and 54. these are different from the main on pins 39 and 44.
This likely explains why there is stereo sound in the headphones. And this doesn't sound as good news unless for some reason the headphone is working in mono.

I propose these other checks:

B/
I guess you checked, but better to ask the question: You have cross checked with the good channel that you can indeed measure the signal? (on cap C249)

C/
If the signal is not comming out of the M61531, let's check if it is getting in. And I guess you already checked that already too.T
Try a different channel such as CD; tuner, tape. These are all different inputs on the M61531 (pins 68 to 80).

D/
If only the main output is dead then the 'Rec Out' outputs for tape and MD on the back of the device might have stereo signal as well. Also to be found on pins 58; 59; 60; 61 on the M61531


Good luck, I think you're going to need it.

[Swake]

Searched a bit for that chip and I'm surprised I must say: https://fixpart.nl/nl/product/view/0005640859?apl=627872
Not certain they can get it as there is 2 weeks lead time.

[roli]

A) The headphone output definitely seems to be stereo
B) I've checked both, yes. The other channel has a signal where it is supposed to be.
C) I've checked all of the inputs now... it's the same on all of them
D) I've checked the REC/AUX output on the back... there is in fact a proper stereo signal there



I've had a look with a thermal camera now as well as my trusted finger... And that chip is getting quite toasty (the hottest part of the image). Definitely can't hold my finger on there. And there is no change in temperature if I have the headphones plugged in or not. So... are we thinking that the chip is dead?

[David_AVD]

The headphone signals are on LOUT and ROUT of IC21 while the ones going to the amp board are on SLOUT and SROUT of IC21.

It looks like LOUT and ROUT also go via IC41 which feeds back into SLIN and SRIN of the volume chip. So the signals for the speaker actually go through the volume chip twice.

Maybe check IC41 or surrounding components in case it never makes it back into the volume chip.

[Swake]

Sounds like that main mixer chip is damaged indeed. But at the same time having only that one output non-functional is a bit weird.

There might be an issue in the vicinity of C248; R215 or IC24 (NJM2068) that pulls the pin 44 to ground or something. -> Remove the cap to isolate the output pin 44 and measure again. If there is a signal  the issue is downstream. I hope the OpAmp B in the NJM2068 is dead because that is repairable.

60°C sounds high yes, although likely still within limit values for that chip. There is a lot going on in that chip, I'm not really surprised it heats up. Eventually you might want to glue an heat-sink on it, something along what is sold for a RaspPi. A short as above might also explain the heat as it has to work much much harder trying to maintain the output.

So the signals for the speaker actually go through the volume chip twice.

I believe you meant 'headphones' instead of speaker. From what I understand the headphones work fine. That loop back is interesting in itself, and I wonder what it does as there is no such thing for the speaker lines.

[Swake]

Balance.... I think it is digitally controller too. Maybe there is a control issue. Try resetting the amp. Procedure is on page 7 "Cold start mode".

Other things:
- Reflow the chip or at least pin 44. There might be a bad connection
- Re-check the power supply voltages.

[David_AVD]

No, I meant the speaker signals. The headphone is taken from the LOUT and ROUT.

The LOUT and ROUT also go through IC41 and back into SLIN and SRIN of the volume chip for a second pass.

SLOUT and SROUT then go off to the amplifier section. It's all there in the schematics.

[Swake]

I see what you mean now. They used the part that was originally designed for surround sound in that chip to implement some 'optimizer' over IC41.
There are 2 SRIN's.
SRIN1 is on pins 9 and 10, this is direct feed without going over IC41.
SRIN2 is on pin 23 and 24 this one passes over IC41.

Both these SRIN's are going over a switch in the chip, somehow there must be a way to switch between then.

[roli]

Well... shit  .
So in order to try and remove the C248 as suggested I needed to remove all of the auxiliary boards and the back panel. That went fine.

Well... then I discovered the first weirdness... C204 on the main board - which is next to IC41 (another opamp) was well... broken off. Most likely shipping damage. The phono preamp board is basically connected to the PCB right next to it, and most likely during shipping this managed to flex enough to break of this cap. One of the pads was lifted and it wasn't touching the other pad. So I resoldered it back... though with the lifted pad not sure quite how good that connection is - didn't try to check it. As far as I understand that is used for the aux input on the front panel - which I never really tried.

After this fix I disconnected the cap as suggested and first tried powering on the amp without any of the aux boards installed. It powered on, displayed the selected input then shut off as soon as it enabled the output (the relay clicked and the thing shut off like a second later). It just flashed the orange LED on front. My guess was that it needs the amp board in order to function. So I placed it back and tried again. Upon powering it on I got greeted by a flash and a small cloud of smoke. Not exactly sure what happened - either the amp board shorted against the input board or the heatsink touched something on the main board... or I missed the alignment on the pin header when reinstalling the board. Anyways after assessing the damage and not really seeing anything, I reinstalled the amp board and tried powering the thing again. This time there was no drama, but the amp is still turning off like it did previously. I tried reinstalling all of the boards and no change.

Well after that I removed the amp board (where the smoke smell is coming from) and looked more closely - it would appear that two traces got blown off... see pictures, but god knows if anything else got damaged. I will try and repair the traces, but I am not sure if that will help.

[Swake]

You have likely found the original issue, that C204 is the root cause of not having the right channel in the first place. As David pointed out IC41 is the 'Optimize' in the block diagram on page 55. And C204 is on the path of the Right signal.

Bottom trace and top trace of amp board seem to be connected with via's. I'm not sure but it looks like one side is going to the bigger caps and the +27V. Replace with a fine wire.

[roli]

Success. The trace repair was fairly uneventful and after that the thing turned back on normally.
And you are indeed correct. Now that the C204 is back in the original position the right channel is in fact back to working normally. I have reassembled most of it and tested it again... and everything seems to be fine.

My only concern is that I am not quite sure how the C204 repair is gonna behave long term. The other pad was ok, so the thing seems to be solidly on there, but the lifted pad hanging by a trace gives me some reason to worry. But I guess if it breaks again i will just insert a small bodge wire between that and R204.

Thank you very much for your help!

[Swake]

That's good news, congrats on your repair

[Audiorepair]

But I guess if it breaks again i will just insert a small bodge wire between that and R204.

So why don't you just do that now?

[roli]

Because I only just now looked at the service manual again and found out where that trace actually goes. Problem is that I would need to take off the back panel again and all of the auxiliary boards and that is a bit annoying. Also as I said... it does feel fairly secure on there, so it may be just fine.

I guess I should also thank engineers at Denon for providing a really good service manual. Probably the best one I've seen.

[Audiorepair]

OK I get that now.

[David_AVD]

Running it without all of the boards connected may not be a wise idea. Sometimes ground traces are routed in a very specific way and a missing board (or ground screw) can really mess with things. The results can vary to hums, no output, instability or wacky voltages that may cause damage.