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Old 9th June 2010, 10:56 PM   #1
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Default I just broke my amp

I've got a Pioneer VSX-1015 AV amp which had a small fault that I thought I could fix myself, but I guess I was wrong.

The original problem was with one of the relays that switch on/off the speaker outputs. It was not working perfectly and caused some problems, so I bought exactly same NAIS ALA2F24 relays and replaced all four of them. (I thought that I just replace all of them at the same time)

The disassembly went just fine, there was no problems changing the parts, the soldering is clean and looks very nice, and the assembly went without problems.

But after putting all together, all I could hear from speakers or headphones was buzzing sound. I disassembled all the needed parts again, checked the soldering and tried to clean everything, put all back together, and when I power it up, I heard a pop from speakers. Now all the speaker outputs puts out -7,6V DC.

I know it is difficult to give advices for this kind of problem, but any help is appreciated. I can provide pictures if needed.
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Old 9th June 2010, 11:01 PM   #2
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Could be the relay wasnt working properly because of the DC output fault ?

It could be as simple as the DC offset needs readjusting.
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Old 10th June 2010, 08:12 AM   #3
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The original problem wasn't that serious.

The problem was, that when I put headphones in, the signal was very weak or didn't work at all in both channels. A small tap to one of the relays had direct affect to this and made the signal to work or break. This was very apparent.

Also, when I powered up the amplifier with quite low volume, usually only left channel was working. Putting more power made the right channel also to wake up, after that I could listen at more lower levels. This was actually quite similar to the headphones too, but tapping the relay had a very clear effect to fix the (usually right) channel.
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Old 11th June 2010, 03:43 PM   #4
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I dissassembled the amp for the third time, bought some PCB cleaner and washed the pcb thoroughly, but the problem didn't go away. I used flux when soldering so the PCB did need cleaning. Maybe I blew some component the first time I connected it, as the PCB wasn't cleaned, don't know.

I took some pictures:

Pioneer1

Pioneer2

Pioneer3

You can see the relays in the second picture. I changed the four that are in a row. I checked my soldering with magnifying glass and it all looks flawless to me.

Now I'm just totally clueless

-Ari
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Old 11th June 2010, 04:36 PM   #5
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I have encountered similar problems in amps like this with single-sided PCBs. They are intermittent and respond to taps, but it is usually a bad solder connection somewhere else and not bad relays.

Some of the big culprits are electrolytic caps because of their size. The other are the inductors where the wire coating was not fully removed at assembly leading to cold solder joints.

Double check all solder joints (not just your relay work) as close as possible, including connectors, wire jumpers, ICs, etc.

Then when assembled, do further tapping with an insulated tool and carefully tap/poke at various components until you find something lose. When you were tapping on the relays before, you may have actually been uncovering an intermittent connection nearby.

Good luck!
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Old 11th June 2010, 04:53 PM   #6
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Quote:
Originally Posted by DCPreamp View Post
When you were tapping on the relays before, you may have actually been uncovering an intermittent connection nearby.

Good luck!
That's a good point. I had this in my mind when I was discovering the fault, but the relay seemed very obvious. But it is not impossible what you said. I try again later to get it work.

There are also few SMD components on the backside of the board. Diodes maybe? Or resistors.

What components are usually the ones that are supposed to keep dc out of the speaker outputs? Or is this impossible to say from the pics?

-Ari
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Old 11th June 2010, 07:21 PM   #7
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There's a lot of possibilities. Do you still have DC offset at all the outputs? If so, there's a problem common to all the amp channels. This all depends on the amp's topology. Ground problem? Lost a V+/- rail? Diodes are unlikely, but again, depends on topology. Things that keep DC out: Feedback, capacitors, current sources, equal supply rails, ground connections, etc. Always do a thorough visual & measure fuses and components (don't assume they're good because they look okay.
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Old 13th June 2010, 05:16 PM   #8
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I just took the amp apart again and went through all the soldering points with soldering iron in hope of fixing a bad joint. (only on the board I was working on before) But just as I expected, it didn't do anything. There is still -7,6VDC in all of the outputs and I'm out of ideas what to do with this
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Old 13th June 2010, 06:25 PM   #9
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This has been mentioned before, but you need to start by measuring the output on the power supplies. Also check that all the fuses in the amp are intact.

You usually get high values of DC on the output of an amp if there's an imbalance in the circuit somewhere. This can happen if you've accidentally soldered two things together that shouldn't be soldered together.

Another possibility is that the relay wasn't a direct replacement and on turn on the output of the amp was connected directly to ground and the output stage died. If the protection scheme built into the amplifier relied on opening and closing the relay, this could be possible.

Replacing any broken transistors is usually a fairly easy task, however this isn't the main concern. You need to figure out why they were destroyed in the first place. The last thing you want to do is replace them, only to destroy them the next time the amplifier is turned on.

Check to see how the output from the amplifier is connected through the relay. And by this I mean the actual output from the power amp itself NOT the positive terminal on the chassis.

The output is likely to be on one side of one of the inductors that is positioned next to the relays in image 2. One inductor per output channel.

When the amp is off is either side of the inductor connected to ground?
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Old 15th June 2010, 02:03 PM   #10
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Something strange happened.

I was measuring voltages from the transformer outputs and then I decided to once again measure the speaker outputs. The DC in the speaker outputs was gone!
I connected a speaker to the the output, but now there is loud buzz/hum in the output, most probably 50Hz mains hum. The transformer also makes some noise itself, but that sounds quite normal to me.

I even got music to play through the amplifier, but the 50Hz hum is loud, easily audible.

I looked through the board and tried to sort out the connections. The connection to each channel is pretty much like this:

Pioneer 4

The lower relay in the picture is one of the four relays I replaced. The relays should be exactly the same part as the manufacturer/model is exactly the same. When all cables were in place, I measured 17K ohms from the coil to the ground.

-Ari S
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