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Pioneer sx 939 sound disappointing

Oldsansui441

Oldsansui441

Super Member
Hi, this is my first post here. I have recently bought a Pioneer sx 939 that was advertised as working but cuts out sometimes and also no fm tuner. I found the main filter caps to be leaking so l replaced these with Nichcon KG's and l also recapped the power supply board and protection board with Nichicon KZ muse and FG. I resoldered all suspect dry solder joints on power supply also.
After doing these repairs l checked and adjusted DC offset and bias voltages to spec, 0mV and 25mV respectively. I have ran unit after repairs for approx 10 hours total and checked dc offset and bias again a couple of times, all ok. The unit has performed faultlessly so far and hasn't cut out once. It does sound reasonably good and has plenty of punch.
My main concern is the receiver does not sound as good as expected when driving my b&w dm309's. I was not expecting this but my Yamaha rx-v740 avr (2003-2004) actually sounds much nicer with these speakers, more controlled bass, especially much more defined mids and crisper highs when compared to the old Pioneer. The soundstage with the Pioneer is also not as broad nor do the separate instruments in the music have their own place as much as with the Yamaha, the Pioneer tends to roll everything in together more if that makes any sense, please excuse any of my terms here.
Is the above to be expected or is it likely that l have further issues with the Pioneer like needing to recap further? I was thinking that maybe the Yamaha even though an AVR might just work better with the b&w's because of its higher current capability, l do know b&w's are known to not be the easiest speakers to drive. Sorry for the long winded post but this is the first LARGER vintage receiver l have owned so have nothing to compare it to, my only other vintage receiver is a little Sansui 441.
Any thoughts would be greatly appreciated.
 
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Thank you for your reply, would you suggest just the main amp board or everything? I know l am asking a lot of questions but this is my first proper vintage project and thanks to this great site l have learned enough to perform the above mentioned work. Maybe l am being a bit critical of this old girl without knowing the condition of the remaining capacitors/components, re your reply. I have also noticed the floor/background noise is slightly higher than l might have expected, is the same in both channels though.
 
I had a sx-950 which had been unused for decades. after getting the power supply rebuilt and the set functioning again, I was disappointed in the sound coming from it. Recap'ed and flowed the control amp. Much better! That was five years ago when I was skeptical of the recapping. Some sets recap'ed don't have a change but others do. My experience is when the set has an impression of playing in a coffee can, recapping is needed. As in: Tinny tops, muddled lows and missing mids. As compared to another set same speakers.
I concur: Recap the Control amp and the EQ board if you like the vinyl.
 
The background noise will probably be a few noisy transistors, in rare cases capacitors can be partly responsible.
 
The control amp is loaded with 2SA725's and 2SC1312's.
 
zebulon1 said:
The control amp is loaded with 2SA725's and 2SC1312's.
Click to expand...

These may be it but all the small caps in the signal path are suspect as well.

Depending on the condition of the existing caps, there can be quite a clean up with all new caps.

But I will warn you that the vintage sound when working well is different than the newer high current sound.

You may not prefer vintage.
 
It's cheap to replace the life limited components in both boards and you'v shown you have the knowledge to do the job. A no brainier.
 
As much as I liked my SX838 a 2000 Yamaha rxv800 is sending it packing.Just more finesse in the sound.Better separation and tighter bass is what I hear among other things.
 
Thank you all very much for your replies, very helpful. If l get a chance in the next few weeks l might recap those other boards. Are 2SA725's and 2SC1312 the only transistors l would need to replace? Are these on other boards also? Zebulon1 your comments on muddled lows and MISSING MIDS is spot on, superdog your comments, Just more finesse in the sound.Better separation and tighter bass is what I hear among other things is EXACTLY the difference l hear also.
I did forget to mention that these symptoms do NOT show up when l use the Pioneer to run my small beovox 1702 speakers, the Pioneer then sounds very much like my little Sansui when driving these, this doesn't much sense to me.
 
There is a TOP TEN WANTED equivalent for PIONEER Receiver Transistors.
The top 3 on the list are below:
1.) The 1st transistors to change in ANY PIONEER that has them are 2sc1451's. These havea round metal heatsink on them so tey are readily identifiable. Replacement is KSC3503. These are limited to the AMPLIFIER BOARD ONLY.

2.) 2SA725 REPLACE on any board it's on. They were low noise (LOL!!) that could and did break down within the 1st year. Breakdown resembles sounds given off by RICE KRISPIES only with a lot more volume.
Use KSA992 for replacement

3.) 2sa726 (See 2SA725) Same replacement as 2sa725.

Replace all of these 1st before any other transistors and after recapping.

DOWNLOAD the DATA SHEETS for EACH TRANSISTOR you purchase. It will have the LEG PINOUT, which invariably WILL be different than the originals. There are 6 ways to insert a transistor, only one of them is CORRECT.

I'm with Zeb on the re-cap. You need to replace all of the lytics, especially the Robin Egg blue SANYO's. These are Solid Aluminum caps in the 1uf to 4.7uf range and they can blow at any time. Same with the tantalums in it. Tant's are ok in most instances just not in AUDIO PATHS.

Some speakers and amps are NOT compatible sound quality wise. The synergy is NOT THERE. Some speakers will sound great on one receiver or amp, but sound like whale crap at the bottom of the Challenger Deep (Mariana's Trench).

My 939 will drive just about anything well as long as it's 8ohm. This is a personal choice for me (I don't use 4ohm speakers unless it's in a console, or it was designed with the unit (KLH-20) and not a problem with the SX-939.
 
recapping is a bit of a misnomer, because it entails quite a few transistors to be replaced. We have had several threads where someone has just cleaned the switches and replaced the electrolytic caps, and complained about the lack of improvement in the sound. THEN they follow the transistor replacement advice, and get BACK the stellar sound these gems are capable of.

Like Larry says, the 2sc1451's. 2sa725 and 2sa726's, but ALSO their complements in each circuit, he 2sc1312 and 2sc1313 transistors.

THAT will cover most of the small signal transistors that are problematic - they don't have to die to turn the sound sour. My parts lists (when authored by me) include far more than just electrolytic caps.
 
Thank you both for your replies, very helpful information, l understand now. My dm309's are 8 ohm but l know what you mean about synergy or possible lack thereof in my case.
Looks like l have a fair amount of work ahead of me, haha, im sure it will be worth it though. Are those blue sanyo caps low loss? Do l have to replace with anything special, there were 2 on protection board l replaced with bipolar elna cerafines, is this ok? Do l use tantalums to replace the like or can l replace with electrolytics? Thanks once again for all of your help.
 
You can replace Tant's with equivalent value lytic's or FILM (mylar) caps IF they aren't too large physically. Generally my limit is 2.2 or 3.3uf depending on the unit's physical layout. Films will last dam near forever compared to lytics.

I tend to stay with one or two brands for caps, especially lytics. For lytics I use Nichicon's. Some guys use Panasonic's or ELNA's.
I use Nichicon UPW or UHE (Low impedance) caps in non signal path areas (power supply, etc.). Then UKL (Low Noise) in signal path. Even a general use capacitor from today is better than original by a few magnitude's of order. Film caps I use are Cornell Dublier DME's for tight spots, or DMT's for larger area's. Axials I'll use the MKT type Illinois cap from AES. In my tube gear I use the same basic stuff, but throw in some K40 or K42 PIO's as output coupling caps. sprague 715P or 716P Orange Drops are good generic film caps, but can sound overly bright in some units.
 
superdog said:
As much as I liked my SX838 a 2000 Yamaha rxv800 is sending it packing.Just more finesse in the sound.Better separation and tighter bass is what I hear among other things.
Click to expand...
I hadn't put my 838 in rotation for a bit until last night.Sounded great.It still is one of the better vintage receivers I have owned.I have always believed that sound is not always better just different.
 
Thanks for your replies. Great advise but l must be missing something, l have gone through service manual a couple of times and l cant find tantalum capacitors in any of the different board capacitor lists? I can only see electrolytic, mylar, styrol and ceramic? I ordered these for two of the small value electrolytic cap replacements l couldn't find in small enough values. I hope these are o.k. http://www.ebay.com.au/itm/290562042455?_trksid=p2060353.m2749.l2648&ssPageName=STRK:MEBIDX:IT and these http://www.ebay.com.au/itm/251964447054?_trksid=p2060353.m2749.l2648&ssPageName=STRK:MEBIDX:IT Had to get off ebay (l know) as couldn't find any from where l normally get all of the other parts.
Is it advisable to replace all electrolytic small value caps with film type as you have prescribed for the tantalums? or just replace electrolytic with electrolytic if small enough values are available. Apologies for more questions but this is all fairly new to me.

Good to hear you like your sx 838, makes me feel better about spending so much time on my sx 939.
 
At work now however I have a before and after picture of the sx1010 control board (very similar to the sx-939 where you can see the culprits most responsible for the decrease in sound quality which I will put up for you this evening.. 28 caps and 8 transistors on this one board and a bit of a pita to get at but can be reworked without disconnecting any wiring. Lay a towel over the main caps. Even though they have bleed down resistors you would get a nasty surprise if you ground out the control amp to them. Also two more tantalums on the phone board as you work your way through the receiver. I have a sx939 in rotation at the moment which has been fully gone through and it sounds great through hpm100's and jbl 100's which combined run about 4 ohms per side. And, as long as you have things this far apart it would be wise to really get after all those push button switch assemblies. Takes several cleanings to get them all working reliably.
One more thing to be mindful of is the dial pointer, find a way to secure it so you do not snap it off while reworking the boards.
-Lee
 
I'm here for moral support as other than cleaning controls I have no electronics skills.Out of close to forty receivers the 838(same family as 939)has been one of my favorites and one of only five vintage receivers I have kept..Mine was given to me(very nice example)because it kept cutting out(those pesky black buttons mentioned here).I got mine working but if the unit sits for a while it comes back. So yes the 939 is definately worth putting some time and effort in.
 
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Thanks guys, that would be great if you could post a pic of your control amp board, l would esp like to see these tantalum capacitors you guys have been talking about, (you mention 2 on the phono board also?). Thanks both of you for letting me know about the push button cleaning l will certainly do that when everything is apart, strangely enough this unit has perfectly quiet/smooth push buttons and controls and l haven't cleaned them yet? Glad to know im not over capitalising on a poor unit, thanks.
 
I just went thru my 939 boards and manual. There are no references to tantalums either in the manual, or on the boards. HOWEVER, that doesn't mean that they weren't used. Usually under 10uf if used at all. If they aren't there don't obcess over it. The Tantalum reference was a general reference to the effect that "if they are there, replace with a film cap. PIONEER substituted parts in their units basically at will, more so at the end of a production run for a unit to empty out parts inventory, and the changes were not made "public". Remember that the manual has a statement on it that states to the effect "that the manufacturer has the right to make changes at any time without notification."

Just for general info Tantalums look like small gumdrop shaped ceramics, but have color striping on them similar to resistors have.
 
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