What? I can't hear you!
February 15, 2012 5:32 PM   Subscribe

Keep and fix or junk?

I just picked up a wonky Sony str-de695 speaker reciever subwoofer combo on Craigslist.

I was advised that the front R/L channels were "low" and after assembling and testing, the rear L surround channel is also low.

After a factory reset, these three channels play at about 10% of other channels while playing the test tone in setup mode.

The front channels do not offer the +/- 10db adjustments available to the surround channels. However, in pure stereo mode, with the amp volume cranked, the audio quality is just fine.

I am puzzled. I am pretty sure I have exhausted programmatic resets, but if reseating a board or a connection might help, I am game.

If the end result is simply that the amp is toast, that's fine. The sub and speaker set was fairly priced without the amp.

Can the amp be repaired, or is it dead?

What can cause a channel to drop so dramatically in volume without affecting quality?
posted by mwhybark to Technology (5 answers total)
 
I don't have a magic bullet answer but here's a bit of troubleshooting for you:
There isn't a -20db/loudness/muting button somewhere that is pressed, is there?
Have you determined that the problem is the amp and not the speakers by switching one of the working channel's speakers to one of the misbehaving channels?
Have you tried toggling between "small" and "large" settings for the fronts? Any change?
Are the channels low with headphones or just with the speakers?
Have you tried both the A and B front speaker terminals? Are they both affected?
Are they low in 2 channel mode or just surround modes?
Have you cleaned the controls with DeOxit? This one's a bit of a last ditch with a newer amp like that but you never know!

If all of that usual stuff has been ruled out you're likely dealing with either bad solder joints (hopefully! But unlikely in an amp that new) or failed components on the problem channels.
posted by tinamonster at 8:28 PM on February 15, 2012


In order, a la email:

There isn't a -20db/loudness/muting button somewhere that is pressed, is there?

---Not that I have noted. Note also that I have performed a factory reset and that in the case of the left rear surround the drop is assymetrical.

Have you determined that the problem is the amp and not the speakers by switching one of the working channel's speakers to one of the misbehaving channels?

--- Yes and no. I moved the front pair from "a" to "b" To no effect. Additionally, with the exception of the visually distinct center bar, the speakers were set up initially after purchase randomly, which would tend to eliminate blowout or in-speaker shorts.

Have you tried toggling between "small" and "large" settings for the fronts? Any change?

--- yes, and no change. Setting "small" for L/R F forces small for everything except the subwoofer.

--- Hm I just remembered there are two-pole powered screwdowns on the subwoofer. I can't see how a stereo or surround signal would reach the sub over A single channel RCA jack, but what do I know?

Are the channels low with headphones or just with the speakers?

--- Have not investigated this, presumably I can only get a L/R F answer to that. Will check.

Have you tried both the A and B front speaker terminals? Are they both affected?

--- Yes, and yes. I had thought I put that in the question, if not, my apologies.

Are they low in 2 channel mode or just surround modes?

--- Both. a&b and also LRS.

Have you cleaned the controls with DeOxit? This one's a bit of a last ditch with a newer amp like that but you never know!

--- No, no special crud cleaner employed.

--- other info: I have a never-deployed as A/V Sony 5.1 (as opposed to this 6.1) in hand and a no-sub set of decent small samsung 5.x speakers, so I can easily eliminate speaker issues. I do think it is the channels in the amp.

So let's imagine it's bad solder joints. Can you be more specific? I have a service manual, a soldering iron, and less caution than you would expect in a 46 year old. As well as experience, productive and not (but EXCITING) in household fixture and socket replacement. Which amounts to: electricity, she bites, but she is a networking problem.
posted by mwhybark at 11:38 PM on February 15, 2012


If you're up for it you can get in there with a magnifying glass and see if any joints on the bad channels look dull, grainy or cracked. You can google "bad solder" and "cold solder" for pictures.
posted by tinamonster at 8:30 PM on February 16, 2012


That sounds like the next step. I'm kinda expecting a write off, though. I isolated for speakers and cable today and as I did that I noticed some transient crackle in the test tone for the rear surround. My conclusion is that the channel outs were badly soldered and are failing roughly together. So I will eyeball it and see if I can get visual confirmation.

If I can, pointing a hot thing at the globs can't really make things any worse, right?

The other a/v unit I have in hand tested fine, so the repair is really optional.

I am amazed that the Craigslist floor for receivers is $50. There are multiple non-HDMI a/v units up against vanilla stereo units, all at $50. Most of the a/v units come with a set of satellite speakers. I saw one 5.1 DVD/receiver/speaker combo for $20.

I'm kind of afraid I will come up with something to do with all those speakers.
posted by mwhybark at 12:31 AM on February 17, 2012


A couple of final thoughts:

I'd remove the old solder and replace it with all new solder for best results. You can wick or pump it away and both are actually pretty fun.

Something else to look for while you are in there inspecting the solder joints: Bad Capacitors. If they are bulging, leaking or cracking they will need to be replaced.

Here is a tutorial that could be helpful if no obvious solder problems jump out at you and you decide to take it on as a project. It's based on car amps but the components in your audio section should be the same/similar enough.

If your amp was older I would strongly encourage you to use Deoxit on the pots, switches, contacts, etc. A six-year-old amp is probably not going to be suffering from a crippling degree of oxidation but I have seen the stuff perform audio miracles so if it were my malfunctioning amp I'd be sure to give it a try. It's especially recommended when there is crackle on a channel or noise when you turn a knob or switch. Here's a primer explaining how to deploy it.

Good luck!
posted by tinamonster at 11:17 AM on February 17, 2012


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