SX 950 Bad phono section.

day67

Super Member
When I had the unit recapped the phono section was "bypassed" in that I didnt have a TT then -- and now do! The tech said the phono sections was, I forget exactly, but "had issues." The quality/clarity, is there but with nothing playing and the volume even up moderately it sounds like wind thru a microphone on a windy day. Also there is random bouts of harsh crackling thru the speakers -- particularly the right channel that occurs at no particular point in the record but is loud and just plain irritating. Cant live with it. Now in any other mode, Aux, FM, etc it is perfectly fine, quiet, no such issues. Is this familiar to anyone? I am likely not going to repair this myself, but will it likely be an expensive repair...due to parts issues or ??
 
That seems to be a common problem on the SX-850 and 950.
If you are handy with a Soldering Iron then it should be a pretty simple fix.
You will want to down load the Service Manual from our Manual Scan Data Base.
Then you will need to order order the 8 capacitors and 6 transistors for the EQ Amp Board the part #s from Mouser and we do have a list of them.
If you choose not to do it yourself then it should be a pretty easy fix for a skilled tech.
Markthefixer should chime in with the final say so.
Steve
 
sx850 sx950 awf011 phono replacement parts

When I had the unit recapped the phono section was "bypassed" in that I didnt have a TT then -- and now do! The tech said the phono sections was, I forget exactly, but "had issues." The quality/clarity, is there but with nothing playing and the volume even up moderately it sounds like wind thru a microphone on a windy day. Also there is random bouts of harsh crackling thru the speakers -- particularly the right channel that occurs at no particular point in the record but is loud and just plain irritating. Cant live with it. Now in any other mode, Aux, FM, etc it is perfectly fine, quiet, no such issues. Is this familiar to anyone? I am likely not going to repair this myself, but will it likely be an expensive repair...due to parts issues or ??

Well, IF you were going to do it yourself, and had soldering / desoldering equipment, you could get away with spending far less than 10 bucks (edit $3.16 w/o ship) in parts, excluding shipping. There are SEVERAL threads on the Pioneer forum about rebuilding the phono amp in the 850, 950 and several remarkably similar phono's on other models. Board # AWF011

But it's not fair to compare the costs of parts where I get my parts and the substitutes I have found that work with a shop's supplier OR a shop's overhead in keeping the parts in stock.

If you have someone else do it, they'll probably take an hour of shop time to do it, at 45 bucks an hour (or more) shop rate.

The phono section is well exposed on the sx950, and after freeing it from the plastic clips, there is plenty of room to work on without disconnecting wires.

Basically the 2sa725 transistors are getting noisy, and working themselves up to a full blown failure.


from mouser.com
Q1, Q2 : 512-KSA992FBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea
Q3, Q4, Q5, Q6: 512-KSC1845EBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea
C1, C2: 1uf 25v 647-UPW1H010MDD 1uf 50v $0.23 ea
C7, C8: 330uf 6v 647-UPW0J331MED 330uf 6.3v $0.39 ea
C11, C12: 3.3uf 25v 647-UPW1H3R3MDD 3.3uf 50v $0.23 ea
C17: 100uf 35v 647-UPW1H101MPD 100uf 50v $0.50 ea
C18: 220uf 25v 647-upw1h221mpd 220uf 50v $0.60 ea

all are currently in stock, changes in voltage reflect either availability or cost versus safety margin tradeoffs.

Note: the transistor lead arrangement on the originals are bce while the replacements are ecb, meaning the flat faces the other way
and the caps are polarized, look for the plus on the board and remember the MINUS lead is marked on the capacitor, be sure the board markings reflect the way the cap you are removing was installed.

The other alternative is to remove the board yourself, send it to me and I will re-do the board BUT you STILL have to solder the wires back onto the board correctly, in the holes where I will remove the pins for you. It isn't that much work to do the caps and transistors WITHOUT disconnecting any wires.
 
Wow, thanks for the quick reply! I have some soldering experience but I am more encouraged that this doesnt look like a nightmare of a job. I do have a service manual, not that good at reading schematics though. Would it be a good time to upgrade on the caps and tweak this section? If so, what would be recommended for an upgrade. I think he previous work that was done in other sections included Elna or Elna Silmics and I know theres Nichicons. Again, thanks for the info -- including parts list -- how great is that! I'll just have to decide if it's a diy or send it out.
 
If it was me I'd purchase a separate phono pre-amp and run it thru one of the tape monitors. Just my 2 cents whatever it's worth.
 
Wow, thanks for the quick reply! I have some soldering experience but I am more encouraged that this doesnt look like a nightmare of a job. I do have a service manual, not that good at reading schematics though. Would it be a good time to upgrade on the caps and tweak this section? If so, what would be recommended for an upgrade. I think he previous work that was done in other sections included Elna or Elna Silmics and I know theres Nichicons. Again, thanks for the info -- including parts list -- how great is that! I'll just have to decide if it's a diy or send it out.
I believe the numbers that you were given for the Capacitors are a good reasonably price upgrade.
I dont know if a local shop would mind you bringing in the parts and just charging labor,a local shop is probobaly not going to be as familiar with these specific units as our AK techs so it is much easier for us to get the proper replacement parts and upgrades.
As far as a seperate phono preamp I would rather just fix the unit (just my 2 cents)
Steve
 
Thanks all...I hadn't thought about a sep phono preamp, interesting idea. I think, though, that since I have gone this far with the 950 that I'll just bring it back via rebuild of the phono sect. I wont be going to any "local shop" for sure, but AK techs, yes indeedy. I can probably remove the board per above and may take markthefixer's advice. Thanks again.
 
Thanks all...I hadn't thought about a sep phono preamp, interesting idea. I think, though, that since I have gone this far with the 950 that I'll just bring it back via rebuild of the phono sect. I wont be going to any "local shop" for sure, but AK techs, yes indeedy. I can probably remove the board per above and may take markthefixer's advice. Thanks again.
Im not sure if you are planning to send it to Markthefixer or if you plan on repairing it yourself,but there is no need to remove the board if you plan on doing it yourself.
If you are doing it yourself Radio Shack sells a inexpensive Desoldering Iron that does the job for $10 dollars.
If not and you do send it to mark then you know that it will be in good hands.
Steve
 
Just remember to have a clean bright desolder tip for good fast heat transfer, otherwise you will end up pushing on the joint and when the foil is hot, it is fragile and can be pushed loose of the fiberglass board.

Do it ONE component at a time, and ask questions when you are not sure.

And avoid heating the polystyrene caps, they are the ones with the clear plastic ends, they are heat sensitive, but you shouldn't be going near them.
 
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Thanks for the advice. A relative "newbee" at this I can use it. If I diy I've learned to go over the process SEVERAL times before diving in -- I'm still undecided. I'll have some time to open 'er up this w/end and really evaluate. I'll let you know for sure.
 
Everything should be done in minor, easily reversable steps, always leaving yourself a graceful exit option. Don't rush, set up in an area where you can walk away from it for a while safely.

Take pictures, when taking things apart, put them back together once first (it always looks different, going the other way) , write everything down, keep the different stages screws and nuts grouped together in plastic bags (later, you'll say to yourself, hmmm 4 screws that all look like ..... THAT.... I remember now...)

Little steps...

Before you know it, it's done.........
 
Well, I think I'm going to attempt the rebuild myself. I'm teased by the idea that when it's done I'll be able to play my LPs without the snapcracklepop and rumble!
First, ordering parts. What brand caps are those from mouser? ...Totally indebted for the info about the transistors (lead position bce to ecb) saw the diagram on another thread. Got it on the polystyrene caps warning. Will keep you all informed as I go ahead with this......I'm sure I'll have questions. Oh Yea, any advice on removing the old caps, cautions etc?
 
They are high temperature long life Nichicon UPW's (the recommended types are nichicon uhe & upw and panasonic fc & Fm.)

Just:

markthefixer said:
Note: the transistor lead arrangement on the originals are bce while the replacements are ecb, meaning the flat faces the other way
and the caps are polarized, look for the plus on the board and remember the MINUS lead is marked on the capacitor, be sure the board markings reflect the way the cap you are removing was installed.

Try to minimize repetitive flexing of the wrapped wire at the pins, the pin is designed to nick the solid wire, which makes a weak spot that likes to break.

Which leads to:
The pins don't take solder well, unless really hot, then the solder holding the pin to the board lets go without it being noticed.

solution: DON'T break the wire in the first place...
 
Basically the 2sa725 transistors are getting noisy, and working themselves up to a full blown failure.


from mouser.com
Q1, Q2 : 512-KSA992FBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea
Q3, Q4, Q5, Q6: 512-KSC1845EBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.06 ea
C1, C2: 1uf 25v 647-UPW1H010MDD 1uf 50v $0.23 ea
C7, C8: 330uf 6v 647-UPW0J331MED 330uf 6.3v $0.39 ea
C11, C12: 3.3uf 25v 647-UPW1H3R3MDD 3.3uf 50v $0.23 ea
C17: 100uf 35v 647-UPW1H101MPD 100uf 50v $0.50 ea
C18: 220uf 25v 647-upw1h221mpd 220uf 50v $0.60 ea

I know this is an old thread, so please excuse me for adding to it. Mark (or anyone from the "Brain Trust"), how important is is to replace Q3-6?

The recap list I had shows the Q1,2 725's as needing replacing, but I didn't order the 1313 replacements as it wasn't on the BOM found in the thread I got it from.

Thanks.
 
These are no longer available :KSC1845UBU (mouser p/n) Q3-Q6.
I ordered KSC1845PBU. From what I could tell from the data sheets this one should be ok (unfortunately it's being discontinued as well).

As far as replacing them as matter of course......From all that I could find the ones most prone to failure were the two PNPs (Q1&Q2). If the noise is still present then you might have to replace the other 4.
 
Well i just ran across this thread when looking for the phono problem as well with my SX 950 . So now i just need to find out the updated part #s to order .
 
I want to thank those who contributed to this thread in the past. I picked up a Pioneer sx850 that had some issues, and the most pronounced was the one described in this thread. I found the thread by Googling, actually. Unfortunately, Mouser had the 1845 transistors on backorder, but I was able to get the 992s that seem to be the most common culprit. I swapped both out of the phono stage board, and it's playing very well. I'll have to get to the others when they arrive. If the interweb did nothing else but provide these opportunities to share the experience and information we have gathered from untold years of work, it would be worthwhile. In fact, maybe it would be best if that were all it was used for....shrug. Thanks again, experts.
 
I bought a SX-850 a month ago, both phono1/2 inputs were dead, no sound, no hum, nothing; i live in a little country in south america, few electronics stores (2), they don't have many transistors, the only thing I could get are BC557 and BC547. I replace A725 with BC557 and C1313 with BC547 (caution with the pinout!), and all capacitors (two 330uF / 6V were very leaky), and the phono1/2/mic section starts to work. It was the best I could do.
 
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