Question about Onkyo TX-SR705 Receiver

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Have an Onkyo TX-SR705 and love it, except it is new emitting EAR SPLITTING popping and drops outs, apparently when it gets hot. It is almost deafening (independent of where volume is set when it happens). Also, it occassionally shuts down completely after such popping. I'm thinking it may be over heating? I also notices that the fans do not appear to be running, but I understand they may be on a thermostat. Haven't seen them run "lately" even when the unit is very hot. Pulled it out of cabinet into fresh air, but problem persists. What do you think it is and is it cost effiective to fix? Thx

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  • pblauvelt Sep 10, 2010

    Putting the unit in Pure Audio seems to reduce or eliminate the popping. No offense to previous expert, but I was hoping for something more than the Onkyo 800 number as a solution (I have that already of course!).

    Is there a way I can test what is overheating, weather the fans are operating correctly, and if they are not, fix or replace? I'm relatively handy with electronic, but have no service manual.

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Hello,

There are a few different potential causes for the symptoms that you describe.
1) Power Supply out of tolerance, is unstable (drifting)
2) Final Amplifiers are damaged, likely due to heat
3) Temperature compensation is faulted.

#1. This is the likely candidate since you stated that you think it is overheating, and the unit is very hot. If the unit is hot enough to be uncomfortable, the fans need to be running. A power supply that has drifted away from tolerances for voltage output can wreak havoc on the other components, if it hasn't already. Shutdown can occur due to thermal reasons, or the output voltages have tripped a protection circuit.

#2. The finals are easily damaged by heat, hence the reason for the massive heatsinks, and forced air cooling. Since most finals are of a darlington configuration, the initial input transistors are likely to be the ones thar are damaged, and will have an unstable gain / HFe, which then affects the main transistors. Shutdown can occur if the finals draw too much current, and trips overload protection. This is likely what has happened, and the finals are continuously drawing too much power for even small signals. This is the only part of the unit where volume control would not have an effect. It just amplifies, usually by a fixed amount, whatever signal comes in.

#3. Temperature compensation works by changing the initial gain in different parts of the circuit so that other parts are not over driven / over worked and presented with too much of a signal that they can't handle. This is mainly directed towards te finals, though temp. comp. is likely built into them. This likely has failed as well, and caused #2.

As for being cost effective, that depends upon your specific situation. If there is a service center nearby, then you should take it there for an estimate. It might cost you $50-100 for this, but it will give you a rough idea of what needs to be done, and associated cost. Many places apply the charge for estimates to the actual repair bill. Some will also apply it to the purchase of another unit, provided you relinquish yours. Personally, I think that your receiver is a sweet setup, and is worth at least the cost of the estimate. If it has been exposed to conditions that may have shortened its life, then you might consider otherwise, or at least tell the service center to cut down on the amount of time that may be required.

Posted on Sep 10, 2010

  • Sheldon Dedek Sep 12, 2010

    Pure Audio is likely a pass through mode, the signal is not amplified or modified. The signal doesn't go through the finals, but it will go through the volume control (I am pretty sure). If you are still getting *some* noise here, you have narrowed down the scope of possible failures. Power Supply will still be suspect, as well as switching elements.

    Without knowing exactly what temperatures the fans are supposed to come on or turn off at, it will be near impossible to tell if they are working correctly. If it is uncomfortable to leave your hand on the hottest part of the cabinet for 10 seconds, and the fans aren't turning, there is something wrong.

    Just for curiosity sake, are you able to put a spare/junkbox fan up against the grill of the amp and see if air circulation from the extra fan helps? If it does, that will confirm a fan issue, though others may still remain.

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It definately sounds like an overheating issue.. I have an Onkyo myself and I love it, but it definately gets hot when in use.. So, here is the Onkyo Support Number for you to call, ok?
For Product Support Team Only:
1-800-229-1687
Hours:
M-F 9am-8pm | Sat-Sun 10am-4pm ET

Posted on Sep 09, 2010

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