Pioneer SX-450 does not power on power but switched outlet works
- Thread starter Lance23
- Start date
The power switches on this model are trouble prone. They can be repaired but doing so requires some patience. Using google, do a search for SX 450 power switch. Follow the links that take you back to Audiokarma. There are several well documented threads that demonstrate various repair methods. The switch is basically like "points" in vintage auto ignition systems. The points build up corrosion over time that can be easily remedied by fine sandpaper or finger nail file. The challenge is getting to the switch. I was able to repair mine without removing it from the chassis but it took most of a Sunday afternoon. No rocket science required, just patience.
Good wisdom from "macyjim"
Some added embellishment:
Check the main fuse for condition and proper rating.
Then bypass the main power switch using a safe jumper.
Build a DBT (Dim Bulb Tester) with a switch, if you don't have one.
Plug the set into the DBT using it as a temporary switch.
This will confirm the poor power switch condition(?) and check the set for any shorts before plugging it in to full house power.
Some added embellishment:
Check the main fuse for condition and proper rating.
Then bypass the main power switch using a safe jumper.
Build a DBT (Dim Bulb Tester) with a switch, if you don't have one.
Plug the set into the DBT using it as a temporary switch.
This will confirm the poor power switch condition(?) and check the set for any shorts before plugging it in to full house power.
Last edited:
merlynski
Curmudgeon Electronicist
If I understand correctly the 'switched outlet' powers on and off with the power switch, but the Receiver stays dark and silent? If so the switch is not the problem.
Look at the schematic, there is a 3 amp fuse (FU6) to the transformer primary that may be blown. It does not affect the switched outlet but will interrupt the power to the Receiver's power supplies. Check the fuse with an ohmmeter (unplug the power cord first), 0 ohms is good. If it is open (bad) something deeper inside may have caused it to blow. If you have a DBT replace the fuse, plug amp into DBT and try turning it on. If the DBT bulb comes on bright for a moment then goes dim try again without the DBT.. If the DBT bulb stays bright the problem is deeper inside. You can build a Dim Bulb Tester for cheap, instructions and explanation are on AK. Zeb is on the right track . . .
phreshboy
New Member
I have the same problem. I have continuity between the switch when on and none when off, I also have switchable current to switchable outlet. However there is no power on the fuses, and jumping the power switch does nothing. I have checked and re-checked the fuses, all test good. There simply is no power getting to the unit. The power cord tests fine and I checked the rectifier diodes as well, all test good. I am fit to be tied here as everything from the power cord to the fuses to the switch seem fine. There is an odd piece of gear bolted to the chassis that I do not know it’s function. Simply a terminal strip like thing with a large disc cap between two of the four posts. Maybe a type of surge protector?
I have learned a lot from this group and seldom post anything so thanks in advance for any help here. Thank you.
I have learned a lot from this group and seldom post anything so thanks in advance for any help here. Thank you.
merlynski
Curmudgeon Electronicist
With Receiver UNPLUGGED from power: find the brown and white wires from the power transformer, follow them to where they are connected. Brown connects to the power cord and one side of the switched and unswitched sockets. White connects to pin 4 of the AWK-060 circuit board. Measure resistance between those two points to check continuity of power transformer primary winding. I don't have one to check myself but I expect somewhere between 75 ohms and 120 ohms. Report your measurement
merlynski
Curmudgeon Electronicist
Good photo, that round device in the heat shrink is a capacitor. The open reading tells me the transformer primary winding has failed open. You will need to replace it to (first step) get this unit working again.
Sometimes transformers have internal thermal fuses that open if they overheat. These fuses are difficult or impossible to replace. The schematic does not show one for this transformer, and low power amps are less likely to have them, from what I have seen. Good luck!
merlynski
Curmudgeon Electronicist
You're welcome! If you become a Subscriber you can post a 'Part Wanted' in Bartertown Parts and some other AKer may have a transformer for a reasonable price.
Watthour
Electron Rancher - JS3600
If the transformer is removed, it can be partially disassembled. There MAY be a thermal fuse under the steel covers, and if it present it is likely bonded to the winding. It can be accessed to check for continuity, and may be replaced with a similar thermal fuse if care is exercised.
Good photo, that round device in the heat shrink is a capacitor. The open reading tells me the transformer primary winding has failed open. You will need to replace it to (first step) get this unit working again.
Hello all to wake up an old thread. I have the same issue, with no power but switch working fine. The round capacitor in the heat shrink in the picture... on my receiver this looks blown. Woult this be the cause of the power issue? Any help would be much appreciated.
There’s a thermal fuse in there. I had a 450 with a dead transformer. Ended up wrecking the transformer trying to get the fuse out though. Not fun.
merlynski
Curmudgeon Electronicist
Not likely that cap is the cause of no power. It is there to reduce arcing across the switch contacts, if it failed open for switch would (maybe) burn its contacts, which might cause a no power situation; if it failed closed (shorted you would not be able to turn off the power. With it unplugged from the wall, measure across the transformer primary winding with your ohmmeter. A good winding/thermal fuse will read only a few ohms, if it reads infinite ohms either the winding or the thermal fuse is open. You can also measure across the switch, one position should be zero ohms, one should be open (infinite ohms). Can you post a picture of the cap?
And welcome to Audiokarma!
Watthour
Electron Rancher - JS3600
If it is an open thermal fuse, this should get you close:
https://audiokarma.org/forums/index.php?threads/sx-450-bando-transformer-d-o-a.827026/
https://audiokarma.org/forums/index.php?threads/sx-450-bando-transformer-d-o-a.827026/
Hello all. I have measured the resistance on the above wires in the previous post. Lools like someone has replace my wires as they are yellow and green. It reads 25 ohm. Think i have measured the correct wires you asked for. I have attached a pic. Tested the switch and its working fine. 0pen loop when off and 27 ohm when tirmed on. I can see some burn marks on tge yello wire. I have also put a pic of that on also. Thanks for your help so far
