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Pioneer SX-550 No POWER where do I start?

jpreza

jpreza

Active Member
Recently picked up a Pioneer SX-550, really nice looking unit. There is no indication of power at all when I switch the power button to Speaker A/B or A+B. Nothing lights up. In reading the forums, these units are known for the AF muting switch issue and the power/speaker switch.

That said, everything I read from AK regarding the power switch is that there is flickering on the power/stereo/lights and static coming from either channel - not the case in my receiver.

I've also tested the AF muting board and checked the DC and AC values per some postings, and so far I get 0V.

I've checked that there is no sound at all, whether I set it to Tuner, AUX or Phono.

Where should I go next?

TIA....JP
 
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What is your level of expertise? At the very least, don't automatically assume that the power switch is bad. You will need to do some basic troubleshooting with a volt/ohm meter.

Check for any blown fuses, above and underneath the chassis.

Use your meter set on AC volts and see if there is 120 volts coming into the switch and then going to the power transformer. If there is no AC voltage getting to the primary of the power transformer, then 99 percent of the time, it is a blown fuse.

I am not familiar with this particular unit but sometimes the power transformer has an internal fuse and in which case, a schematic will tell for sure.
 
cademan said:
What is your level of expertise? At the very least, don't automatically assume that the power switch is bad. You will need to do some basic troubleshooting with a volt/ohm meter.

Check for any blown fuses, above and underneath the chassis.

Use your meter set on AC volts and see if there is 120 volts coming into the switch and then going to the power transformer. If there is no AC voltage getting to the primary of the power transformer, then 99 percent of the time, it is a blown fuse.

I am not familiar with this particular unit but sometimes the power transformer has an internal fuse and in which case, a schematic will tell for sure.
Click to expand...

I have a decent multimeter. I checked the fuses and they are good - there's actually five of them so I was careful to inspect each one and checked for continuity.
 
I also did a basic testing on the voltage coming out to the power lamp (which I believe it should be 6 or 8 V DC) and I get 0V. All my lamps are dead but I need to troubleshoot the power issue before installing new ones.
 
ivandezande said:
Jumper the power switch
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I used a short jumper cable with alligator clips. I got a little spark when I closed the circuit, but still nothing - voltages are still reading 0V on the AF muting board and no sound output anywhere.

I suspect that maybe the power supply is dead. :thumbsdown:
 
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Have you checked the AC voltage into and out of the mains transformer, and then the DC downstream of the diodes? And other power supply voltages?
 
1st thing I do on a dead unit, is to measure resistance between the 2 prongs of the main AC plug. Unit unplugged, power switch engaged, you should measure the resistance of the transformer primary winding. I'd expect a low resistance near 100 ohm. Maybe 50, but not 5, nor 1000.

Measuring directly at the AC plug confirms (or not), the fuses, wiring, switch, are closing the circuit.
 
You must check the power switch. It's easy on this model if you connect your volt-meter probes into the "switched" AC outlet located on the top right corner behind the receiver. You have two AC outlets behind the receiver; one has AC voltage whatever the position of the power-speaker switch and the second outlet (switched) has AC voltage only when the power switch is ON. Needless to say that your SX-550 must be connected into the power line.
 
elnaldo said:
1st thing I do on a dead unit, is to measure resistance between the 2 prongs of the main AC plug. Unit unplugged, power switch engaged, you should measure the resistance of the transformer primary winding. I'd expect a low resistance near 100 ohm. Maybe 50, but not 5, nor 1000.

Measuring directly at the AC plug confirms (or not), the fuses, wiring, switch, are closing the circuit.
Click to expand...

Thanks! I think you may have found the problem. I set the switch to ON with the unit unplugged, measured the resistance across the prongs, and it is OPEN. So do you think I may have a bad power cord?!
 
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ecluser said:
You must check the power switch. It's easy on this model if you connect your volt-meter probes into the "switched" AC outlet located on the top right corner behind the receiver. You have two AC outlets behind the receiver; one has AC voltage whatever the position of the power-speaker switch and the second outlet (switched) has AC voltage only when the power switch is ON. Needless to say that your SX-550 must be connected into the power line.
Click to expand...

Thanks! I thought maybe it was going to be as simple as replacing the power cord. I took the power switch out of the equation as being the culprit, because (per your suggestion), When the power switch was in the OFF position, the unswitched outlet read 118V AC and the switched outlet read 0V AC. When I turned the switch to the ON position, both outlets measure 118V AC as expected.
 
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It seems to confirm that the power switch is good but I've fixed many similar Pioneer receivers and almost everyone needed a restauration of the contacts inside the power switch. I mean that your meter might show 118VAC but keep in mind that your meter has a very high resistance (probably 10MOhm) and with a load the power switch might be defective. On the primary side of the transformer, you have a fuse. Check that fuse with your Ohm meter and make sure the fuse makes a good contact into the fuse holder.
 
Well I've cleaned the power switch. Took me a while to take it apart but it looked pretty clean. I made sure to reassemble it exactly the same way. Still no power and I've checked the fuse directly behind the power switch. I even went ahead and replaced it.

Sadly now when the switch is off, the unswitched outlet reads 118V AC, but the switched one reads 45V AC?! I'm not sure what I did wrong. So at this point I'm stumped.
 
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If you jumper the power switch, take your volt meter and make sure that there is 120 volts going into the primary side of the power transformer. If you have 120 volts going into the primary side of the power transformer., with the black meter probe on the chassis (ground), use the red probe to see if there is any AC voltage on the secondary of the power transformer.

You do know what primary and secondary means don't you? I am on a tablet at the moment so I am going to have to switch computers so i can look up a schematic for your 550 so I can tell you which wires are the primary and which wires are the secondary.

If you are proof positive that there is 120 volts going into the primary of the power transformer but nothing coming out of the secondary windings, then the power transformer itself is bad.

I'll get back to you within the hour. If not, someone else will chime in and hopefully give you some good instructions.
 
The unswitched outlet is directly connected to the AC mains.

The switched outlet is going through the switch obviously.

I'd discard any switch issue soldering a jumper across it by now.

If you still measure open circuit from the AC plug, like you did before, the circuit is not closed and the unit won't power on. Don't discard a burned transformer.
 
cademan said:
If you jumper the power switch, take your volt meter and make sure that there is 120 volts going into the primary side of the power transformer. If you have 120 volts going into the primary side of the power transformer., with the black meter probe on the chassis (ground), use the red probe to see if there is any AC voltage on the secondary of the power transformer.

You do know what primary and secondary means don't you? I am on a tablet at the moment so I am going to have to switch computers so i can look up a schematic for your 550 so I can tell you which wires are the primary and which wires are the secondary.

If you are proof positive that there is 120 volts going into the primary of the power transformer but nothing coming out of the secondary windings, then the power transformer itself is bad.

I'll get back to you within the hour. If not, someone else will chime in and hopefully give you some good instructions.
Click to expand...

I'm a newbie so not sure what you mean by primary or secondary.
 
elnaldo said:
The unswitched outlet is directly connected to the AC mains.

The switched outlet is going through the switch obviously.

I'd discard any switch issue soldering a jumper across it by now.

If you still measure open circuit from the AC plug, like you did before, the circuit is not closed and the unit won't power on. Don't discard a burned transformer.
Click to expand...
 

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As you can see in the picture, the switch is in the off position, yet I’m getting 44 V AC from the switched outlet.
 
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