Denon AVR-3300 - intermittent audio out

[Ken123]

Hi, Y'all...

I got a good deal on this off eBay. The seller indicated problems, but they
seemed to involve only digital sound inputs. I mainly planned to use it for
analog sound, so I figured that would be no problem.

It worked great for a few days until sound output to the speakers started
disappearing when I switched input sources, including tuner.

While troubleshooting, I discovered if I flexed the top of the Audio/DSP
card the sound would return, and the receiver would start working
normally...for a while. The speaker relays can be heard switching when it is
operating normally, but not when it isn't.

Then again a little later, no sound after switching sources. Again I flexed
the card and the sound returned. So, brilliantly, I figured keeping the card
flexed with a small cable tie would solve my problem! It did - for a few
days. Then the problem returned.

I removed the card and inspected it carefully, and could not spot any
obvious smoking gun. All solder joints, traces, connectors look normal. No
bulging caps.

With these meager clues, is there a Denon AVR expert out there who could
suggest what I should look for? Thanks.

Ken

 

[William Sommerwerck]

The problem with bad solder joints and cracked traces is that they are often
difficult-to-impossible to see.

We recently had a similar problem that was traced (joke intended) to a
cracked trace under an IC.

I would start systematically unsoldering and resoldering every joint on the
board. It's not enough to melt the solder and push it around. You need to
suck or wick it off, then apply fresh solder, preferably eutectic (63/37).

 

[Arfa Daily]

The problem with bad solder joints and cracked traces is that they are
often
difficult-to-impossible to see.

We recently had a similar problem that was traced (joke intended) to a
cracked trace under an IC.

I would start systematically unsoldering and resoldering every joint on
the
board. It's not enough to melt the solder and push it around. You need to
suck or wick it off, then apply fresh solder, preferably eutectic (63/37).

How does your company make a living dealing with such dry joint problems by
sucking or wicking every joint before resoldering ? Just interested, as I
sure wouldn't be able to spare the time to approach it like that, and still
keep it financially viable. For sure I agree that just reflowing the joints
is not really enough, but I don't think that I know anyone else in the trade
who deals with bad joints in any way other than just reflowing with a touch
of new solder added, whether they are reworking an obvious bad joint, or
carrying out a 'blanket solder-up' job of an area that has an invisible bad
joint.

I do sometimes clean old solder right off, but only when there are obvious
signs that the chemical composition of the joint has deteriorated beyond
recovery - for instance where a joint has gone crystalline as a result of
being subjected to continuous heat-stress from the component that it is
connecting.

To the OP. I have had a number of problems with bad connectors on Denon AV
amps. Just because the connectors 'look' good, I wouldn't immediately
dismiss them as being blameless. It would be worth squirting some switch
cleaner in, and then 'working' the connector in and out a few times. Also,
if you have the facilities / expertise, its worth reworking the joints on
the surface mount DSP ICs

Arfa

 

[William Sommerwerck]

How does your company make a living dealing with such dry-joint

problems by sucking or wicking every joint before resoldering?

It doesn't. I'm an individual who's been repairing electronic equipment, on
and off, for almost 50 years.

I learned a long time ago that there are two ways to repair something --
find out exactly what's wrong, or do whatever's needed to get the damn thing
working again. Neither is the "best" approach -- it depends on the problem.

In this case, it looks as if there's a bad solder joint -- or perhaps a
cracked trace. It's less trouble to systematically resolder the joints than
try to find the "bad" one. Note that two recent posters to this group have
had good luck doing basically that.

The problem with just adding a bit of fresh solder is that there's no
guarantee you're really getting the solder into its "liquidus" state. It's
better to remove the solder altogether, so you can see what you're doing. If
you have a SoldaPult, or a similar tool, it's not much trouble to quickly
remove the solder from a dozen or so joints.

 

[Ken123]

I would start systematically unsoldering and resoldering every joint on

the
board. It's not enough to melt the solder and push it around. You need to
suck or wick it off, then apply fresh solder, preferably eutectic (63/37).

To the OP. I have had a number of problems with bad connectors on Denon AV
amps. Just because the connectors 'look' good, I wouldn't immediately
dismiss them as being blameless. It would be worth squirting some switch
cleaner in, and then 'working' the connector in and out a few times. Also,
if you have the facilities / expertise, its worth reworking the joints on
the surface mount DSP ICs

I appreciate the suggestions. There are about 70 pins connecting the
Audio/DSP board, but I think I'll go ahead and re-solder each of them.
However I had to remove about 100 screws to disassemble this thing, and I'll
have to pretty much reassemble it to test whether the resoldering worked.
But what the hell, I'm retired!

Ken

 

[Smitty Two]

The problem with bad solder joints and cracked traces is that they are often
difficult-to-impossible to see.

We recently had a similar problem that was traced (joke intended) to a
cracked trace under an IC.

I would start systematically unsoldering and resoldering every joint on the
board. It's not enough to melt the solder and push it around. You need to
suck or wick it off, then apply fresh solder, preferably eutectic (63/37).

No, but it's enough to add a drop of liquid flux to each joint and
reflow it. Solder isn't spackle that you spread around. Wicking off all
the old stuff just to put on new stuff will take about thirty times
longer than adding some fresh flux, which is what you're *really* doing
when you put on fresh solder.

 

[Arfa Daily]

No, but it's enough to add a drop of liquid flux to each joint and
reflow it. Solder isn't spackle that you spread around. Wicking off all
the old stuff just to put on new stuff will take about thirty times
longer than adding some fresh flux, which is what you're *really* doing
when you put on fresh solder.

Agreed.

As far as the practicalities of removing old solder go, I have a proper
vacuum rework station which removes solder from a joint almost as quickly as
just resoldering it, but I still wouldn't, under 'normal' circumstances, use
it to remove the solder from every joint on a board before resoldering. I
think that it's probably down to a degree of how much time you have on your
hands and personal preference, if you are an experienced solderer. I only
questioned your original post because you said in it "we recently had a
similar problem ..." I (obviously wrongly, sorry !) assumed that "we"
referred to a repair shop. I don't have a problem with you using this total
removal technique if that's what works for you.

I agree that sometimes a joint which appears to flow when an iron is
applied, may not have reached a correct liquidus state throughout, but as an
experienced solderer yourself, I'm sure that you would agree that when this
happens, it is pretty obvious to the 'knowing eye', and that's the time I
reach for the vacuum iron.

I would however, question the technique from a professional point of view,
for finding *most* bad joints. There are very good techniques for finding
the rogue ones - a can of freezer spray for instance - and a 'blanket'
resolder of an area is always a last resort for me, if all other methods
have failed. Particularly on a densely packed board, a 'blanket job' opens
the way for creating further problems with unintentional ( and unspotted !)
whiskers across joints. With the best will in the world, I think we would
all agree, it happens ...

Interesting to hear how other people go about jobs, and how the juggling act
of practicality versus profitability is looked at and resolved by
individuals.

Of course, there's lead-free bad joints to contend with now, and as we all
know, they defy *all* the proper techniques that we know and love ...

Again, to the OP. As you surmise, you will probably want to screw it back
together before retesting - particularly any screws which pass through the
back panel into phono ( RCA ) socket blocks which have a built in grounding
strap at the screw hole. Some of these AV amps are super-critical of rear
panel grounding, and can cause you no end of problems with the protect
circuit cutting in with the slightest disturbance, as ground connections
come and go ...

Arfa

 

[Mark D. Zacharias]

Hi, Y'all...

I got a good deal on this off eBay. The seller indicated problems, but
they
seemed to involve only digital sound inputs. I mainly planned to use it
for
analog sound, so I figured that would be no problem.

It worked great for a few days until sound output to the speakers started
disappearing when I switched input sources, including tuner.

While troubleshooting, I discovered if I flexed the top of the Audio/DSP
card the sound would return, and the receiver would start working
normally...for a while. The speaker relays can be heard switching when it
is
operating normally, but not when it isn't.

Then again a little later, no sound after switching sources. Again I
flexed
the card and the sound returned. So, brilliantly, I figured keeping the
card
flexed with a small cable tie would solve my problem! It did - for a few
days. Then the problem returned.

I removed the card and inspected it carefully, and could not spot any
obvious smoking gun. All solder joints, traces, connectors look normal. No
bulging caps.

With these meager clues, is there a Denon AVR expert out there who could
suggest what I should look for? Thanks.

Ken

In my experience this is a matter of resoldering the flat-pack IC's on the
DSP board. Your average doit-yourself-er is unlikely to have the necessary
soldering skills or equipment to deal with the fine pitch of the IC leads
involved.

Mark Z.

 

[jango2]

Hi,
I just fixed a Denon AVR-1905. I'm probably one of the 2 recent
posters that William refers to. I'm not familiar with the AVR-3300 but
i just wanted to point out that the problem might not lie in the DSP
board. When you flex the pcd you might be subjecting the cpu board to
stress causing a pin of the cpu to make /break contact, as it is the
main board and other pcbs dock onto it. I think you should reflow the
cpu. I finally resolved my case with the use of a scope, service
manual and magnifying glass. Observe and trace waveforms like data and
clock all the way to the pins of the cpu. Like William said, my break
was under the flat pack.
Jango.

 

[Ken123]

Hi,
I just fixed a Denon AVR-1905. I'm probably one of the 2 recent
posters that William refers to. I'm not familiar with the AVR-3300 but
i just wanted to point out that the problem might not lie in the DSP
board. When you flex the pcd you might be subjecting the cpu board to
stress causing a pin of the cpu to make /break contact, as it is the
main board and other pcbs dock onto it. I think you should reflow the
cpu. I finally resolved my case with the use of a scope, service
manual and magnifying glass. Observe and trace waveforms like data and
clock all the way to the pins of the cpu. Like William said, my break
was under the flat pack.
Jango.

I'll check that out. Thanks.

Ken