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Pioneer SX-450 Power / Selector Switch Cleaning

mclendo

mclendo

New Member
I was sitting back listening to my SX-450 the other day when I started getting intermittent static in one channel or the other. The static also occurred whenever I touched the power/selector switch. A quick look on the forums indicated to me that my problem lay in the contacts of this switch, and that getting to it to clean them wasn't much fun. So last night I decided to spend a few hours and work some on the SX-450. I also decided to take pictures for noobs like myself of the process step by step. I probably (err - definitely) could have done better, so those of you who are electronics whizzes, please feel free to chastise me for bad form and poor decisions so that others don't repeat any mistakes I made that I didn't know I made.

First - my baby, the SX-450 in all its late 1970's glory:
01.jpg


If you decide to do this repair yourself, do so as I did - at your own risk:
02.jpg

03.jpg

04.jpg


After removing the side panels by removing the two screws in each one, you can remove the top panel by removing the screws on the left and right back corners (picture shown with screw already removed):
05.jpg


Removing the top panel reveals the well laid-out inside of the SX-450:
06.jpg


Now we can see our target, the rotary switch, but we can't get to it just yet:
07.jpg


A little closer view:
08.jpg


The next step is to remove the front panel from the unit. To do this, first you must remove all the knobs. On my unit, they all just pulled off (including the large tuner knob). I've read that some units (higher model numbers in particular) have a hex screw in the tuner knob which must be loosened:
09.jpg


Next, remove the two screws on the top of the front panel:
10.jpg


Finally, the nuts on the selector switches must be removed, and the front panel will be free:
11.jpg


Next, the black plate beneath the tuner frequency selector must be removed:
12.jpg


There are a bunch of screws which must be removed to do this. Note one of the screws is a little hard to find - on the right side recessed back under the right side of the frequency selector. I can't recall exactly, but I think that the nut from the balance dial has to be removed as well:
13.jpg


Next, the tuner needle and string must be freed from the black plate. Do this gently. I managed to not break the string during my repair. I imagine that breaking this would make the repair a lot more difficult than it already is, so I recommend being very careful not to break it. Also - a question to more experienced folks - is this where you would calibrate the needle (by adjusting it's location along this string)? :
14.jpg


Go on to the next post for the rest of the instructions
 
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With the black plate freed, it can be removed from the system. It is now time to remove the bottom of the unit. This is very straightforward unscrewing of screws:
15.jpg


Now, the mounting plate for the selector switch and eq pots must be removed. There are two screws underneath, a screw on either side of the headphone jack, and the mounting nuts on the eq pots which must be removed for this:
16.jpg


Now we are ready to desolder this little sucker. This was my first time desoldering much of anything, and all I had was a wick to do so. I think that a solder sucker/vacuum pump would have been better, but I didn't have one. I'll be going by the local electronics store to get one before my next project like this. The contacts that are going to be desoldered are all those in the line of contacts that connect to the PCB of the rotary switch. They are really easy to find on the board. Also, be careful to not put too much stress on the switch's pins. I managed to break the end of one off, but I still have a good connection so I'm not overly worried about it:
17.jpg


Make sure you are able to pull the switch contacts away from the PCB, then flip the unit back over. The next step is unmounting the power supply so that you can get to some things that it blocks. This is done by unscrewing the 4 black screws on the side of the unit (no pictures). Set the power supply carefully in a convenient location (there may be a better place than the one I chose). Next, find the red and white wires which go to the power portion of the rotary switch (the plastic part). Free them from the wire harnesses that run from along the bottom edge of the unit. You will probably have to free a couple other wires too, just make sure to remember which ones you do unhook:
18.jpg


Now you can pull the switch out from the unit. Remember what wires it threads over/under so you can put stuff back the way it was (probably not a big deal but like most engineers I'm just a little OCD):
19.jpg


Now you can take the switch apart. Here is the part of the switch that needs cleaning badly (note the pin I broke off - oops!):
20.jpg

And the back:
21.jpg


Clean the contact areas thoroughly. I used some 600 grit sandpaper which seemed to do the trick nicely. I cleaned both the rotary contact pads as well as the little clamps they make contact with by sliding the sandpaper through the clamps like the contact pads would slide through.

Note, if you decided to take apart the power part of the switch (which I did), make sure you put it back together correctly (which I didn't). If you don't you'll likely end up with a unit that doesn't turn off. Just take a look at it and make sure that when it goes back together, the long contact arm is on top of the short contact arm. I was able to fix this without having to desolder the switch again, but it took a while with a pair of needle nose tweezers and a lot of concentration to pull it off.

Now, put everything back together and you will hopefully be static free. I haven't had time to listen at length, but I no longer get static when I touch the output selector switch.
 
Very nice tutorial :)

Now, you did clean the contacts inside the gray plastic holder right?

This is where the biggest culprit is. The contacts in there need to be cleaned. I used emery paper on my SX-550 and that fixed it:thmbsp:

Good job and the instructions
 

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I did a little cleaning of those contacts, but they actually hadn't suffered from any problems with oxidation/arcing. My issue lay with the output selection part of the switch.
 
Nice post & pics. Welcome aboard. The 450-750's, I believe all suffer from that dreaded switch. Very good sounding units. I've had 450/650/ & 750's.
I've always been partial to the sound of the X50 series over the X80 series.
The 850 has a seperate toggle switch for the power. :thmbsp:
 
This thread was from the "pre-deoxit days", nowadays deoxit would be sprayed on the wafer and the deoxit loosens the black stuff coating the metal, after which repeated actuation of the switch will scrub the contact areas clean - leaving a bright streak plowed through the black.

The more usual problem is burned power switch contacts, in the gray plastic assembly at the end of the switch, which has to be opened and abrasively cleaned.

The pictures are from a sx-550, but the sx-450, sx-550 and sx-650 are very similar, and the sx-750 is very similar, with a different, riveted switch.

index.php


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link to other threads upon the subject
 
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I have the same unit, and it's 15wpc are astounding. I have a little static burst when I turn it on, but fine (so to speak) after that. Now I just wish I knew how to get, or if it's possible to adjust it properly. I get about 43mV offset on the R channel, L channel is great (around 10mV).
 
Ancient post, but this is a fantastic tutorial - thank you for taking the time to post this mclendo.

I've got an SX-450 with severe static in the left channel. The right channel is fine. I followed this procedure here hoping that the issue was the switch contacts, but unfortunately I don't think it was. I buffed out the contacts with 600 grit sandpaper and they looked wonderful, but there must be something else going on with my unit. I've hit all the controls with D5/F5 so I don't think it's a dirty control. The only thing I haven't done yet is burnish the contacts on all of the internal fuses. I'll try that at some point too.

-Matt
 
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EE -

If you start a new thread in the Pioneer Forum, your unit will get all the attention it deserves. As a rule, there is nothing in the power supply section which would affect only one channel. While it won't hurt to clean the fuse clips and ends, it likely won't solve the issue.
 
I realize this is an old thread. I picked up a 450 yesterday for $20, guaranteed to work at a flea market... Had this problem (blinking lights, crackling sound from power switch).

I took the assembly apart today and cleaned it, de-oxit, acid brush, then used some emery paper on the contacts inside that grey plastic box. Just got it all back together and one small problem.. The unit will not shut off now. It sounds great, a/b/a+b speaker switch works as it should except when I put to the off position, nothing. Lights stay lit, no sound. Did a re-assemble the unit incorrectly? Or is this a problem that doesn't have anything to do with that switch do you think?


-Tom
 
mclendo said:
With the black plate freed, it can be removed from the system. It is now time to remove the bottom of the unit. This is very straightforward unscrewing of screws:
15.jpg


Now, the mounting plate for the selector switch and eq pots must be removed. There are two screws underneath, a screw on either side of the headphone jack, and the mounting nuts on the eq pots which must be removed for this:
16.jpg


Now we are ready to desolder this little sucker. This was my first time desoldering much of anything, and all I had was a wick to do so. I think that a solder sucker/vacuum pump would have been better, but I didn't have one. I'll be going by the local electronics store to get one before my next project like this. The contacts that are going to be desoldered are all those in the line of contacts that connect to the PCB of the rotary switch. They are really easy to find on the board. Also, be careful to not put too much stress on the switch's pins. I managed to break the end of one off, but I still have a good connection so I'm not overly worried about it:
17.jpg


Make sure you are able to pull the switch contacts away from the PCB, then flip the unit back over. The next step is unmounting the power supply so that you can get to some things that it blocks. This is done by unscrewing the 4 black screws on the side of the unit (no pictures). Set the power supply carefully in a convenient location (there may be a better place than the one I chose). Next, find the red and white wires which go to the power portion of the rotary switch (the plastic part). Free them from the wire harnesses that run from along the bottom edge of the unit. You will probably have to free a couple other wires too, just make sure to remember which ones you do unhook:
18.jpg


Now you can pull the switch out from the unit. Remember what wires it threads over/under so you can put stuff back the way it was (probably not a big deal but like most engineers I'm just a little OCD):
19.jpg


Now you can take the switch apart. Here is the part of the switch that needs cleaning badly (note the pin I broke off - oops!):
20.jpg

And the back:
21.jpg


Clean the contact areas thoroughly. I used some 600 grit sandpaper which seemed to do the trick nicely. I cleaned both the rotary contact pads as well as the little clamps they make contact with by sliding the sandpaper through the clamps like the contact pads would slide through.

Note, if you decided to take apart the power part of the switch (which I did), make sure you put it back together correctly (which I didn't). If you don't you'll likely end up with a unit that doesn't turn off. Just take a look at it and make sure that when it goes back together, the long contact arm is on top of the short contact arm. I was able to fix this without having to desolder the switch again, but it took a while with a pair of needle nose tweezers and a lot of concentration to pull it off.

Now, put everything back together and you will hopefully be static free. I haven't had time to listen at length, but I no longer get static when I touch the output selector switch.
Click to expand...

Disregard my last post... I obviously did what the OP did... What a PITA..lol
 
I just picked up a 650 for $20. But of course I didn't read up on common problems, and this seems to be the number one issue. Mine flickers and has a slight sizzle for a short time, and then seems fine. But tell me, why does it work after a while? Why doesn't it just keep flickering? Maybe it's just not bad enough yet.

The other issue mine has is that volume pot works very "heavy." I've hit it with contact cleaner and lube, but I think it might need a second shot.
 
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