Pioneer SX-850 Phono Stage Question

Discussion in 'Pioneer Audio' started by MAXZ28, Nov 8, 2010.

  1. MAXZ28

    MAXZ28 Addicted Member

    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.

  2. dumptruck

    dumptruck AK Subscriber Subscriber

    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.
  3. w1jim

    w1jim I can fix it but good... Subscriber

  4. MAXZ28

    MAXZ28 Addicted Member

    Thank you, sir! :thmbsp:
  5. Tarl Of Gor

    Tarl Of Gor AK Subscriber Subscriber

    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
  6. Eagle1

    Eagle1 Super Member

    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.
  7. phillman5

    phillman5 New Member

    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: Nov 15, 2011
  8. eddiel

    eddiel Active Member

    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).


  9. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber

    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.
    Last edited: Dec 7, 2011
  10. eddiel

    eddiel Active Member

    ^^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.

  11. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber

    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?
    Last edited: Dec 9, 2011
  12. eddiel

    eddiel Active Member

    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. :)
  13. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber 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.
  14. eddiel

    eddiel Active Member I replaced all the transistors 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 :)
  15. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber

    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.
    Last edited: Dec 20, 2011
  16. eddiel

    eddiel Active Member

    Yes as I learned it is an acquired skill!! But at least I learnt something, mainly do not open the switches. :)

    I made sure to put the three connectors in the same way as the original transistors. I mapped out the original set up before removing them. But I'll check them again.

    Thanks for the ebay heads up.

  17. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber


    There is NO correlation between the replacement transistor's lead layout and the original - usually the safe assumption is that it is different!!

    in this case the old transistors had a rarer lead arrangement.
    2sa725p bce
    2sc1313 bce

    usually when people use the exact transistor I recommend in a thread, they also get the lead layout configuration in the data I list:
    512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.17 ea
    512-KSC1845FTA (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

    which you probably noticed and overlooked in your search for local parts.

    you HAVE to know the EXACT layout of the transistors you have purchased, or figure it out using meters and testing, and with a non-gain testing conduction only meter, you will be able to locate the base, but will be unable to reliably distinguish the collector and emitter.

    installing them backwards (probably what happened) may damage them.

    best way out of this? get the 992's and 1845's and go by their datasheets (and the info I copied out on them).

  18. eddiel

    eddiel Active Member

    Thanks a lot mate. I got some reading to do. Both those transistors are available at mouser but the shipping makes them ultra expensive (to Canada) so I'll check my local shop to see if they have those specific ones.

    I really appreciate all your help. :)
  19. markthefixer

    markthefixer ESCAPED:armed & dangerous Subscriber

    The local shop should tell you the layout of the transistors they sell you.
  20. eddiel

    eddiel Active Member

    I never thought to ask. The guy who served me wasn't just the help as well i.e. he plugs in the transistor number you give him and the computer tells you what the replacement part is. Hence he wouldn't have thought to tell me either. The main guys weren't there at that time of day unfortunately.

    Anyway, I'm going into town today and will see if they have the ones you listed above. Otherwise I'll buy from Mouser. Thanks again for your help. I can't express my gratitude enough. I'm learning and enjoying the process at the same time :)

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