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Pioneer SX727 Channel Noise!

TellMeWhy

TellMeWhy

Active Member
Hi everyone,
My much loved Pioneer SX727 has developed a nasty noise on one channel, and I wonder if someone can suggest what might be the cause? The receiver is in very good condition, and has worked fine for years, but developed the fault after being switched on for longer than usual (8 hours plus...).

The noise is on the R channel only, is very loud, and sounds like crackles and surface noise of an old and very scratched vinyl record. I have isolated the noise to the the power amp section.

So, without going into details, can anyone hazard a guess as to what might be causing these bad crackles on one channel of the power amp? Bad capacitor?

Cheers in advance!
Jon
 
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Are you sure it's in the amp section? Like all SX x2x series, it has a ton of 2SC1213's and 2SA725's in the preamp which go noisy and leaky.
If it is in the amp section, could be a transistor, capacitor less likely I would think but they should be replaced anyways.
 
ivandezande said:
Are you sure it's in the amp section? Like all SX x2x series, it has a ton of 2SC1213's and 2SA725's in the preamp which go noisy and leaky.
If it is in the amp section, could be a transistor, capacitor less likely I would think but they should be replaced anyways.
Click to expand...
Hi, thanks, yes it is definitely the power amp section, on one channel only. Very loud noise. Transistors on the power amp board makes sense...
 
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I assume you disconnected the pre-out/main-in jumpers to determine the static is in the power amp (or after in the signal path)? Remember the protection board comes after the power amp and before speaker outputs. Some chance your problem could be there.

In my experience, this is likely transistors on the power amp. If you want to take a conservative approach (which I favor) I would swap transistors on the channels since the two channels are identical. Q1-4 are all the same (2SA572). Swap Q1 and 2 then Q3 and 4. See if the static moves from one channel to the other with one of those swaps. If not, you can move on to the next transistors. If the static moves with a transistor swap, you've identified the bad transistor. None of the transistors on the SX-727 power amp board (AWH-011) are on the "bad transistors" list, so there is no obvious place to start. It's possible the exposure to heat for the extended time you had the receiver on pushed one of the transistors over the edge.
 
KeithD said:
I assume you disconnected the pre-out/main-in jumpers to determine the static is in the power amp (or after in the signal path)? Remember the protection board comes after the power amp and before speaker outputs. Some chance your problem could be there.

In my experience, this is likely transistors on the power amp. If you want to take a conservative approach (which I favor) I would swap transistors on the channels since the two channels are identical. Q1-4 are all the same (2SA572). Swap Q1 and 2 then Q3 and 4. See if the static moves from one channel to the other with one of those swaps. If not, you can move on to the next transistors. If the static moves with a transistor swap, you've identified the bad transistor. None of the transistors on the SX-727 power amp board (AWH-011) are on the "bad transistors" list, so there is no obvious place to start. It's possible the exposure to heat for the extended time you had the receiver on pushed one of the transistors over the edge.
Click to expand...
Thanks Keith, that is a great, and relatively easy approach to finding the bad transistor!
 
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