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Old 12th February 2008, 05:44 AM   #1
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Default Pioneer HT receiver... blown channel?

I bought a Pioneer Elite VSX-56TXi home theater receiver new in August '07 and was enjoying it until last week. I'd been using its passive bi-amplification feature to bi-amp my speakers--it doubles the front channel outputs through the rear-surround outputs.

A few days ago, I turned on the receiver and noticed that the left speaker's tweeter wasn't playing. After some troubleshooting, I determined that the left rear-surround output was only outputting a faint signal relative to the other channels.

Have I fried/blown a channel? What steps should I take to determine the cause?

I plan to try a factory reset tomorrow (couldn't hurt), and if that doesn't help, I'll open it up, give the inside a visual inspection, and post some pictures.
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Old 12th February 2008, 07:34 AM   #2
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It it an IC output amp, or does it use discrete transistors?
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Old 12th February 2008, 08:31 AM   #3
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It uses Pioneer's "Advanced Direct Energy MOSFET" technology, which appears to be on a chip. So, my guess is discrete transistors.
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Old 13th February 2008, 07:35 PM   #4
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I opened up the VSX-56TXi today and took some pictures. It's a beast! It's fairly clear to me that I won't be able to troubleshoot it myself, but perhaps I can narrow down the problem to make the fix easier for a technician later.

Overall View
Click the image to open in full size.

Power section, main capacitors, speaker outputs at top
Click the image to open in full size.

Closer view of speaker outputs, faulty channel is left-most output
Click the image to open in full size.

I saw a lot of capacitors from Chemi-Con, but a lot of blue Elnas used elsewhere. Feel free to comment on what you see... I also have other pictures if it would help to see the rest of the receiver.
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Old 14th February 2008, 04:30 AM   #5
TheMG is offline TheMG  Canada
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No toroids

Why is it that manufacturers always insist on using EI lamination transformers and not toroids which are better all-around? Cost?

Anyways, I don't want to divert from the original topic too much.

Couldn't find any datasheets on those chips, def looks like something proprietary. Possibly some kind of chip-amp or multiple FETs in a single package. Gonna be kinda hard tracking down the signals not knowing how this thing works. The techs will have access to service manuals, which in a case like this are going to come in very handy.
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Old 14th February 2008, 08:36 AM   #6
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Thanks for the response! I don't mind any diversions if I'm learning more about amplifier technology. What's the difference between a toroid versus a square laminated transformer?

Do you have any idea how difficult or expensive this will be to diagnose and repair? I'm not sure what's reasonable to expect to pay for this sort of fix.
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Old 14th February 2008, 10:33 PM   #7
TheMG is offline TheMG  Canada
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The main advantage is due to very low stray magnetic fields, which reduces electromagnetic interference, lowers idle current, improves efficiency thus the transformer also runs cooler. Toroids also have better regulation than EI lamination transformers, meaning the output voltage does not drop as much as the load is increased, which makes these transformers ideal for audio applications. Too much supply voltage fluctuations in an audio amplifier application is undesirable. Smaller size and weight for a given power rating.

Disadvantages are that they are typically more expensive, as the manufacturing process is somewhat more complicated. Whereas EI transformer windings can be wound before being inserted onto the core, toroids have to be wound around a one-piece donut shaped core. I'm guessing this is what's keeping many manufacturers of consumer audio equipment from using them, cost.

Here's a neat video showing how these things are wound: http://youtube.com/watch?v=_EJ0nzvgN-E

Last but not least, because of all the advantages of toroids, comes a side effect. That is, power-on inrush current is much higher which necessitates a "soft start" circuit when using large toroid transformers.


You could say I'm a big fan of toroids, and probably many of the other people on this forum are too.
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Old 15th February 2008, 11:14 AM   #8
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Pretty cool. That will be something to look for if/when I get a separate power amplifier. Even the little Radio Shack Accurian amp I hacked apart had a toroid, after all...

Do you have any opinion or advice about my other question: how much should I expect to pay to have this fixed?
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Old 15th February 2008, 09:30 PM   #9
Nrik is offline Nrik  Denmark
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Default Re: Pioneer HT receiver... blown channel?

Quote:
Originally posted by infinitesymph
A few days ago, I turned on the receiver and noticed that the left speaker's tweeter wasn't playing. After some troubleshooting, I determined that the left rear-surround output was only outputting a faint signal relative to the other channels.[/B]
Did you ever get to reset it?
Áre you sure it is not the settings, the speakers or the wires?
You should doublecheck in the setting menu, the test tone, and by switching the cables for left and right surround.

There is no need to fix something unless it is broken.
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Old 15th February 2008, 10:14 PM   #10
eyoung is offline eyoung  United States
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hello all,

I had a similar problem that was after a lot of consternation a poor connection at the driver inside the speaker cabinet.


Good Luck,

Elwood
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"Lead me not into temptation...I can find it myself."
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