Pioneer SA-9500 Integrated amp tripping speaker protection - diyAudio
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Old 3rd December 2016, 03:06 PM   #1
Brawndo is offline Brawndo  United States
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Default Pioneer SA-9500 Integrated amp tripping speaker protection

Title mostly explains. The amp would run for about 10 minutes and shut off. I suspected the relay, so I opened it up and cleaned the contacts. It ran for a little longer but still less than an hour. It's possible that the longer run time had nothing to do with my cleaning the relay. I had it at a lower volume this time, so that may account for the increased run time.

After it shut off this last time, I felt around inside but nothing I could feel was even the slightest bit warm.


Looking for the next step in trouble shooting, thanks.
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Old 3rd December 2016, 03:16 PM   #2
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Check for DC on the speaker lines.
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Old 3rd December 2016, 06:20 PM   #3
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Well, that's a start. Reading around -120mV on the right and over -250mV on the left.
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Old 3rd December 2016, 06:33 PM   #4
Mooly is offline Mooly  United Kingdom
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Both those are high in real terms.

DC offset is checked directly across the speaker terminals (as long as the relay hasn't tripped) and with no signal present.

Odd to have both channels so high. A scope check to make sure no AC was present would be my next move.
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Old 3rd December 2016, 06:38 PM   #5
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I don't own a scope. But I checked DC just like you said. Across the speaker terminals with no signal, volume all the way down.
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Old 3rd December 2016, 06:44 PM   #6
Mooly is offline Mooly  United Kingdom
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A scope is pretty much essential for most fault-finding.

Always check the basics... which means checking all the rails are correct including any lower voltage rails running the front end of the power amp. Its odd to have both channels with a lowish and yet significant offset.
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Old 3rd December 2016, 07:35 PM   #7
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I am seeing some incorrect voltages coming off the power supply. There's a 48v pin reading around 40v. A 35v reading below 30v. Things like that. I'm noticing a fair amount of heat coming from one of the transistors. It's attached to a heat sink next to an identical transistor that doesn't seem to get as hot. There's also a slight hair-dryer-like smell coming from the area.
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Old 3rd December 2016, 08:10 PM   #8
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I just checked the voltage on the bases of the two transistors. The schematic says one should be 48.8 and the other -48.8. The negative one reads a little over -50, the positive one reads around 40. This is the one that's getting hot.
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Old 3rd December 2016, 09:12 PM   #9
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That's peculiar. There's precious little on this regulated +48V supply itself that could be drawing excessive current - it is feeding the VAS current sources (Q5, Q6) and the main preamp section. It is, however, also supplying and serving as a reference for the cap multipliers for the +35V and +24V supplies, so all of these are naturally going to be off as well.

Please check voltage drop over R13. If that's about 7 V, we can conclude it's not excessive current draw on +35V/+24V that's the problem.

What do you see in terms of unregulated voltages in front of the +/-48V regs?
If these are nice and symmetrical, it might just be an aged Q1. I find it interesting that they'd use a TO220 case 3 A job there, looking at stuff I don't think it has to supply more than about 150 mA or so. Maybe for better cooling - it'll have to dissipate 1-2 watts if the unregulated voltages are the nominal +/-60V I suspect.
If the + supply is much lower, I'd suspect overcurrent. Maybe one of Q5/Q6 can't sustain its C-E voltage any more or something.
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Old 4th December 2016, 12:14 AM   #10
Brawndo is offline Brawndo  United States
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Voltage drop on R13 was 6-7 V. I measured the unregulated voltages on the collectors of Q1 and Q2 and they were symmetrical. So it looks like Q1 is the culprit?
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