Yamaha RX-V675 receiver with one noisy channel

[maidez]

I have a Yamaha RX-V675 receiver that has started producing static / pops on the front right channel. I've downloaded the service manual, and am familiarizing myself with the contents of the manual as well as the diagnostic menu. So far, I've learned:
- All of the values / tests available in the diagnostic menu are within normal range / successful
- The noise is present even when muting the unit via the service menu, and also when selecting the 1 kHz test tone for the affected channel
- The noise is moderately loud, and doesn't seem to react to adjusting the receiver volume
- The problem is somewhat intermittent, but usually will present itself after the receiver has been on for just a couple of minutes
- I've disassembled the unit and checked the main board for leaking capacitor or obviously burned components, and to my (relatively) untrained eye, have not found anything obvious. I've looked at the solder joints, but being a software guy, I'm not sure that I'd recognize a bad joint unless it was really obvious.

I have a multimeter and a soldering iron, and a basic knowledge of circuits from physics courses way back from my college days. I've completed a number of successful electronic projects, but am a bit out of my element knowing where to get started with trouble shooting. Any tips on common failure points or a general approach I should take to identify the source of the noise would be greatly appreciated.

[Armadillo]

Is the "POP" a "LOUD" intermittent "POP" regardless of volume control or what pop is that ? When you say statics? is that a crackling noise or hissing noise? Is it possible to attach a noise recording?

I would isolate the amp board from the pre-amp modules to identify the source of the noise, example, swop signal to FR/AE of the long tail pair with signal to FL/AE of its long tail pair [see main 1/2 schematic]. Is the POP still from the FR channel?

[maidez]

I'm sure my description of the noise leaves something to be desired... Attempting to clarify:
When I first turn on the receiver, audio sources play normally. Then usually the noise will start adding to the signal on the right channel. It sounds somewhat like the static you would hear when tuning between radio stations, but it's much less homogeneous than white noise, with the loudness (and perhaps the pitch?) varying, and at times even stopping for a couple of seconds. Less frequently, there is a sharp transient noise that I called a "pop". As I mentioned, the noise doesn't seem to be affected by adjusting the receiver volume, and is even present once it's started with the muting enabled. I don't think that I've happened to be adjusting the volume when a "pop" has occurred, so I'm not sure if it's also not affected by volume control.

In looking at the Main 1/2 schematic and at the board, I can swap R with L signals pretty easily at connector W103 because it's just wires in a connector, but I believe that's well downstream from what you are referring to. I'll try and see where the preamp signal enters at the left of the "Main 1/2" diagram to see if it's something I know how to reroute.

Thanks for your help. I'm trying to relearn amplifier circuits and terms like long tail pair, but it's a bit of a stretch for me at the moment.

[Armadillo]

hi,
The source of the noise could comes from capacitors and even resistors. The POP I was referring to is the unmistakable type, it is so loud at maximum volume "BOOM" even your volume control was set to minimum or even muted.

It can even be as simple as noise from dirty contacts -> cleaning your contacts like from those selectors switches or input connectors.

So the best approach I would suggest to you is to isolate the areas of search.



https://www.eevblog.com/forum/repair/yamaha-rx-v675-receiver-with-one-noisy-channel/?action=dlattach;attach=293610;image[/url]

[maidez]

Yes, thanks. I saw what you were referring to in your previous response, but wasn't immediately able to find where these signals originate on the board. After spending more time with the layout, I've now identified the physical components that correspond to this area of the block diagram. One question before I tear into the board further:

The signals for FL and FR are on solid wire jumpers on the surface of the board (J158 and J159 respectively) shown in section D4 on p.122 of the manual. When troubleshooting by rerouting signals like this, would a knowledgeable person clip the wire, and jumper the signal for testing, then subsequently repair the wire, or desolder the jumper (or a through board component if there was not a convenient jumper like this), and temporarily solder in wire for testing?
My normal debugging processes don't involve modifications in the physical world, so I don't want to start this new activity by doing something stupid.

Regarding your comment on the contacts -  the selector / tone controls are mostly electronic, so apart from the volume knob there's not much for me to clean.  Since the noise is heard even when using the internal test tone I don't think input connectors are likely culprits, but I appreciate the suggestions and circuit guidance.

[Armadillo]

My normal debugging processes don't involve modifications in the physical world, so I don't want to start this new activity by doing something stupid.

Hey dude;

There are so many possibilities if you had the intention to think, for example unpin the pins from the plug!. But hey dude, don't do it, I don't think you have the intention to be practical anyway and as otherwise you may think its stupid again, the risk of breaking the pins or even bend the wires of your priced amplifier.
With just a soldering iron and a multimeter, go had it your correct ways of your normal debugging process and with your theories, and may some able members be able to better assist you.

 

[maidez]

Not sure if there is a communication barrier, but I'm sorry if I offended you. I appreciate your help to this point, and what I was trying to convey is that I have very little experience with board level repair, though I have basic skills and an ability to learn.  I've read a lot and have now watched a ton of you tube videos, but I just haven't come across something simple like the 'normal' way to reroute a signal, so was appealing for help from the community.

I know that beginners can be a pain, and don't mean to cross a line when asking basic questions. The receiver is broken, I'm just trying to keep it out of the landfill, so I'm OK with damaging it further if that's the outcome of working on it with my lack of experience.

[mzacharias]

I have a lot of experience on Yamaha's. Personally I would just replace the differential transistor pair (Q1005 and 1006) for that channel. There has been some history of problems in this area. Since disassembly is required, I would also replace Q1017 and Q1031. They are not expensive. Additionally I once saw bad solder on one of the diodes D1007 and D1008 cause a similar symptom. They were surface-mount if I recall correctly.

[DimitriP]

When troubleshooting by rerouting signals like this, would a knowledgeable person clip the wire, and jumper the signal for testing, then subsequently repair the wire, or desolder the jumper (or a through board component if there was not a convenient jumper like this), and temporarily solder in wire for testing?

See what happens when there is no "DMM" , "oscilloscope" or "best probes in the subject title? 

If you have easy access to desolder a component (or a jumper wire) do that.


You don't even need to "swap channels",  disconnect (or clip) the jumper) and  see  (hear) if the noise is coming in from the pre-amp or if it's generated by the final stage.

If you are really in the mood for swapping stuff, swap the input caps and see if the noise follows the cap.

[maidez]

mzcharias - Thanks for the specific advice. Judging from the user name similarity, I think it's your videos that I've been watching on You Tube, thanks for putting those up, they've been very useful for getting an overview of the process.

DimitriP - Thanks for the tips. I'll wouldn't have thought to listen with the jumper clipped/removed, so I"ll definitely add this step to my adventure.

With all of the advice, I definitely have some work ahead of me. I'll report back after I've made some progress.