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  #1  
Old 11-08-2010, 03:23 PM
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MAXZ28 MAXZ28 is offline
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Pioneer SX-850 Phono Stage Question

I have been using my SX-850 as my garage receiver and I noticed that the phono stage has lost a channel but comes back if I flip to MONO. All the other inputs are fine in STEREO but both PHONO1 and PHONO2 will only play both channels in MONO. Sounds fine although every now and then I hear a snip or tiny tick like I'm playing a dirty record. I cleaned the switch several times already with deoxit to no avail. So now I'm not using the PHONO stage since I'm convinced it's in need of a recap.

What should I be looking at? Any insight would be greatly appreciated.

Thanks.
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Old 11-08-2010, 03:29 PM
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Um, doesn't that mean you're just listening to one channel of phono on both speakers? Since even in my very limited experience doing tech work I have come across three receivers/integrateds with dead transistors in the phono stages, that would be my suspicion. Assuming you have confirmed output from the TT, of course.

After echowars walking me through the first one (and the only valuable one), I did my troubleshooting on the others by following the signal path with an audio probe. It gets a little confusing when there is feedback, but by comparing to the working channel it wasn't too hard to figure out where the problems started.
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  #3  
Old 11-08-2010, 03:34 PM
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You can rebuild the awf-011 phono board in a jiffy for short money and it'll be better then ever. Here's your link...
http://www.audiokarma.org/forums/sho...ighlight=phono
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  #4  
Old 11-09-2010, 09:37 AM
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MAXZ28 MAXZ28 is offline
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Thank you, sir!
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  #5  
Old 11-09-2010, 09:53 AM
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Tarl Of Gor Tarl Of Gor is offline
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My Spec-1 was doing that and I started playing around with the function control and it started working fine. That may be all it is, just a dirty function control pot or even a tape source switch.

Guess you already tried cleaning it huh? lol
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  #6  
Old 11-09-2010, 10:43 AM
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Quote:
Originally Posted by MAXZ28 View Post
I have been using my SX-850 as my garage receiver and I noticed that the phono stage has lost a channel but comes back if I flip to MONO. All the other inputs are fine in STEREO but both PHONO1 and PHONO2 will only play both channels in MONO. Sounds fine although every now and then I hear a snip or tiny tick like I'm playing a dirty record. I cleaned the switch several times already with deoxit to no avail. So now I'm not using the PHONO stage since I'm convinced it's in need of a recap.

What should I be looking at? Any insight would be greatly appreciated.

Thanks.
Check your phono interconnects. One of them could be bad. To make sure swap the left and right phono cables amd listen in stereo to see if it moves to the other channel. I'd check them before digging into your 850.
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  #7  
Old 11-15-2011, 11:26 PM
phillman5 phillman5 is offline
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Thumbs up phono input to SX 850

Like an earlier poster noted, I had one of the transistors on the phono equalization board go bad. Open the bottom, its the board on the left, half way to the back, with the front of the receiver toward you, has 7 wire wrap connections. pin three is left channel in, pin 5 is right channel. I just replaced all three transistors in the bad channel, note they are not the same.

If all other inputs work this is maybe the problem especially if both phono inputs don't work.

I have also had the selector switch need cleaning. I could get the bum channel to work by holding in the phono button. You can actually take this board out, and open the switches to clean the contacts WELL. Just using something in the front won't do it.

Last edited by phillman5; 11-15-2011 at 11:53 PM. Reason: corrections
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  #8  
Old 12-07-2011, 07:02 PM
eddiel eddiel is offline
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I thought I;d revive this thread rather than start a new one since I am having problems with my SX-850 phono stages (both 1 and 2).

There is a lot of noise coming through both phono 1 and 2 inputs even when there's no t/t attached. It's not grounding as I tried attaching the grounding wire of the t/t and it made no difference.

I also opened up the receiver and cleaned out the selector switches as described above by phillman5 above (i.e. I did open them up to clean them properly) but no luck.

I'm thinking maybe I have the same issue with noisey transistors. My question is how do I figure out which transistor(s) might be causing the problem.

I got the unit for free because of these problems so happy to learn on it but at the same time it's such a nice unit that I don't want to make it worse! I'd rather it go to someone else than ruin it so any guidance would be appreciated.

I did look through the manual and I think the offending board is the one marked AW011 (which is located pretty much where phillman5 is indicating in the post above).

Thanks

Eddie
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  #9  
Old 12-07-2011, 09:30 PM
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Quote:
My question is how do I figure out which transistor(s) might be causing the problem.
you don't

you replace all 6, because even if you can localize it to one channel, the other channel is well on the way to failure.
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Last edited by markthefixer; 12-07-2011 at 09:33 PM.
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  #10  
Old 12-09-2011, 04:14 PM
eddiel eddiel is offline
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^^Thanks mate. I wrote down the two types of transistors I need to replace:

2SA725 and 2SC1313. I popped into a shop to get these and he plugged those numbers into his computer database and gave me the following:

For the 2SA725 - A844 (It's what's written on the transistor)
For the 2SC1313 - C644 (ditto)

But I've been doing some research on here and found a thread which has the following listed for the above:

2SA725 - KSA992FBU
2SC1313 - KSC1845UBU

Which obviously are different numbers.

Can I use the ones I bought (no worries if I have to throw them out they cost virtually nothing) or are they fine to use?

The shop is a well known shop and isn't run by novice types so I assume it's fine but I just wanted to double check.

I did do a google check on supplier of the above two KSXXXXX but could only find the A992 replacement. The C1845 seemed harder to track down.

I just want to make sure I don't make matter worse with the SX-850

As usually thanks for all the help.

Eddie
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  #11  
Old 12-09-2011, 11:36 PM
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ksa992 - the alphabet soup on the end is variable depending upon supplier, same for the ksc1845.

you can try your devices ( I didn't have time to look up their specs - I'll just trust the shop's judgment here), it is just convenient (for me) to get those, and they ARE very quiet.

worst comes to worst, you take your local stuff back out.

you in the UK? Or are you in New Zeland? Or was I a complete miss, and you are in Australia?
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Last edited by markthefixer; 12-09-2011 at 11:39 PM.
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  #12  
Old 12-10-2011, 08:02 AM
eddiel eddiel is offline
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Quote:
Originally Posted by markthefixer View Post
ksa992 - the alphabet soup on the end is variable depending upon supplier, same for the ksc1845.

you can try your devices ( I didn't have time to look up their specs - I'll just trust the shop's judgment here), it is just convenient (for me) to get those, and they ARE very quiet.

worst comes to worst, you take your local stuff back out.

you in the UK? Or are you in New Zeland? Or was I a complete miss, and you are in Australia?
Thanks again. I'll try the ones I bought since I have them. If there's too much noise I can try and find the ksa992 & ksc1845.

I have a SX-939 which is starting to develop similar issues with the phono stage (you can only hear it if the volume is turned up all the way) so this SX-850 is a good training ground.

I was in the UK, but I'm back in Canada now.
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  #13  
Old 12-10-2011, 04:13 PM
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markthefixer markthefixer is offline
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Quote:
Originally Posted by eddiel View Post
Thanks again. I'll try the ones I bought since I have them. If there's too much noise I can try and find the ksa992 & ksc1845.

I have a SX-939 which is starting to develop similar issues with the phono stage (you can only hear it if the volume is turned up all the way) so this SX-850 is a good training ground.

I was in the UK, but I'm back in Canada now.
mouser.com on the N. Am. continent... our favorite parts source... may even be a mouser Canada...

the 939 has transistors in the amp that may be doing it as well.
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  #14  
Old 12-19-2011, 08:08 PM
eddiel eddiel is offline
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Hmm...so I replaced all the transistors and...no sound at all. There's a very very faint buzz which I am used to as you sometimes hear that when dealing with a phono input but that's it. The AUX, FM and AM work perfectly fine but both Phono 1 and 2 have no sound at all. I double checked the t/t on another system so I know it's working fine.

I think I might have damaged the selector switches when I opened them up to spray contact cleaner in them. I had trouble getting them to work after I closed them up and it took a couple of tries. I noticed a piece of metal on both was giving me issue as it had come loose but I managed to get it back. Both switches move in and out but possibly I messed up the internal contact.

Are these switches easy to source? I can replace them as it's just a solder job but not sure where to get the switches.

Other than the switches I can't think of what else it could be. I double checked the solder job on the new transistors and they all look good (nice and sealed).

Any suggestions for replacement switches?

This is my project job so happy to experiment with this receiver to learn.

Eddie
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  #15  
Old 12-20-2011, 12:37 AM
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exactly how did you determine the correct way to connect the transistors ? There are 6 ways to connect some of them, and only one will work. I need reassurance that they went in correctly.


function pushbuttons from ebay on the boards... there's a buy it now auction (360411448368) with the board.

you can press the straw up to the top holes at one end and squirt, which will fill the entire switch. NO OPENING NEEDED

opening switches is a skill, an acquired skill.
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Last edited by markthefixer; 12-20-2011 at 12:44 AM.
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