Pioneer SX-535 Right Channel Static Advice Needed

[ChuckinNC]

I have a Pioneer SX-535 that I bought new and have used occasionally over the past many years. For the past several years it would occasionally "pop" on the right channel only when it was turned on. Over time this became louder, and would occasionally lead to a static storm that would last for 10 to 20 seconds. I discovered this site, and researched similar issues. I found several threads that seemed identical to my problem, so after studying those, I was confident I could trace this down. I replaced the capacitors and transistors on the right channel amplifier only AWH-035 board except for C21, since I concluded that should affect both channels. Maybe I am wrong there. I did not replace the output transistors.
Much to my disappointment, it seems worse now. The current symptoms are a faint static hiss on the right channel even with the volume to minimum. The static hiss remains on the right channel independent of the balance control position even at minimum volume. I still get the popping and static storm that will last for 10 to 20 seconds and seems to be worse as the unit warms up. I am thinking that the equilizer board AWF-014 transistors could be suspect.
I am not sure what to tackle next, and any advice or experience would be appreciated.

 

[dcgibby]

Did you clean all the switches and controls? Much of what you're describing can be caused by dirty or faulty switches and controls.

 

[Binkman]

Welcome to A.K.
Certainly cleaning eliminates that factor and mey help per above.
What you have or had are noisy transistors with a bad history of same if those were replaced? with what? and which ones? replacing the caps improved the circuity and thus the noise more prominent. likely the output transistors are ok
Perhaps this is relevant if you haven't read it.
https://audiokarma.org/forums/index...remely-loud-noise-issue.896407/#post-13359602

This one is more relevant to your static storm
https://audiokarma.org/forums/index.php?threads/sx-535-screw-up.924514/#post-14013503

 

[century tek]

No offense but you probably should have read up just a teensy bit more. You really can't assume or guess with these kinds of things.

Probably should put it back the way it was as you now learned that just throwing parts at it is not going to be the solution.

Usually static in one channel is a small differential transistor. Off the top of my head, I want to say that it is a 2SA798 transistor. It's a little two-in-one jobber with 5 pins but can be replaced with two separate transistors. Pioneer was famous for using these.

 

[dly66]

The schematic has 2SA763 for the differential pairs on the amp card (Q1-Q4), but many times they used the 2SA726. The latter can go bad turning into a static storm after the unit warms up, maybe 5-10 minutes from a cold start. The longer it is on the worse it tends to get. Picked up a fix and repair Sansui 771 and replacing the 2SA726 differential pairs in it made the storm go away. Replaced 4 transistors and had a nicely operating unit. A number of problem transistors were used in this vintage Pioneer but those would be my first candidate to go after. The 2SA726 has a bad reputation, as far as I know the 2SA763 tends to hold up well. In the Sansui the 2SA726 is not the ones shown for those spots on the schematic. 2SA798 is a five leg transistor that does the same job but commonly used later in the 70s.

Picked up a cheap SX-636 fix and repair from Binkman, sold untested and cordless he said it was crackling, replaced the 2SA726 pairs and the pair of 2SC1451 on the amp card before putting a cord on it, after bringing up and setting the bias it had no problems when using the FM tuner. That got rid of the crackling.

With the SX-535 the differential pairs should be the four in the front middle of the amp card, the ones closest to those big reddish brown film capacitors. KSA992 were used to replace them. Board shown after capacitor, transistor, and trimmer replacement. Still has the original outputs. An SX-535 was my first project, currently on loan to a friend while I diagnose and fix the old Onkyo I gifted them a few years ago.

 

[Binkman]

from Binkman, sold untested and cordless he said it was crackling

((I test everything I sell ))
Hey mate! got you linked above. Yeah OP needs to dig in and post what p/n's he's got and didn't replace.
-----------
Chapel hill was dead w/lock down, moved to the Coast living in my Bro's house, now. very very low covid stats.
emails in my profile.

 

[ChuckinNC]

The schematic has 2SA763 for the differential pairs on the amp card (Q1-Q4), but many times they used the 2SA726. The latter can go bad turning into a static storm after the unit warms up, maybe 5-10 minutes from a cold start. The longer it is on the worse it tends to get. Picked up a fix and repair Sansui 771 and replacing the 2SA726 differential pairs in it made the storm go away. Replaced 4 transistors and had a nicely operating unit. A number of problem transistors were used in this vintage Pioneer but those would be my first candidate to go after. The 2SA726 has a bad reputation, as far as I know the 2SA763 tends to hold up well. In the Sansui the 2SA726 is not the ones shown for those spots on the schematic. 2SA798 is a five leg transistor that does the same job but commonly used later in the 70s.

Picked up a cheap SX-636 fix and repair from Binkman, sold untested and cordless he said it was crackling, replaced the 2SA726 pairs and the pair of 2SC1451 on the amp card before putting a cord on it, after bringing up and setting the bias it had no problems when using the FM tuner. That got rid of the crackling.
View attachment 2026247
With the SX-535 the differential pairs should be the four in the front middle of the amp card, the ones closest to those big reddish brown film capacitors. KSA992 were used to replace them. Board shown after capacitor, transistor, and trimmer replacement. Still has the original outputs. An SX-535 was my first project, currently on loan to a friend while I diagnose and fix the old Onkyo I gifted them a few years ago.

Thank you for all the replies. I bought a kit that contained all the capacitors, transistors and diodes from Ebay for the amplifier board. . The right channel of the amplifier board AWH-035 had the two 2SA763 transistors, which I replaced with KSA992. I then replaced the other three transistors on the right channel part of the board. The kit included the two diodes, and replacement capacitors, which I have also installed. I have not touched the left channel, as it is working fine. I was over confident in my abilities, since I expected this to be an easy fix by replacing the suspect 2SA726 transistors. When I got into it, my board did not have those transistors. Much to my disappointment, things did not get better after all this.

 

[Binkman]

Well, you have a good channel to compare Voltages to. assure you have the caps polatity installed correctly.

 

[dly66]

There are other potential vintage transistors that can get noisy in the unit. There are the 2SC1318 on the amp card and there should be some 2SC1344 on the switch/control board (tone controls). The volume and balance pots (VR2 and VR1 in the schematic) are both upsteam of the 2SC1344s that should be on the control board so they would have no effect on noise from them. In some units the volume control is between the tone board and the amp board.

If something acts up as it warms up freeze spray can be used to chill transistors as the problem starts and if chilling them calms them down for a time then you have likely found a culprit. Have used that technique to ID a differential pair that were acting up doing a rat-a-tat-tat that were transistors that get little mention (likely uncommon - it was an old Sherwood). A can of canned air (duster) turned upside down may be usable as freeze spray, not sure about the issues using them that way. Probably a bit awkward. I have cans of Dust-Off looking up the msds sheets it is listed as being flammable.

Have had an amp that developed periodic bursts in the background and freeze spray did nothing but gently tapping on individual transistors with a hard plastic tuning tool caused the culprits to start making some really weird noises I would not expect transistors to make (out of the amp through the speakers). Replacing those two on the channel got rid of the issue. It was a cheap GW find Yamaha amp that had a blown driver transistor and after playing fine for a period after the original repairs the static burst issue on the same channel began. A pair of 2SA844.

Based on this old bad 11 transistor list I found years ago and saved a copy to my drive the 2SC1344 can develop a static burst issue.

I think the SX-535 I picked up had 14 transistors of 5 types on this list in it. They were well represented on the amp card, tone board, phono circuit (equalizer board), and the last two on the tuner board. I obviously did not use the KSC2690 on mine. Often there is a commonly recommended replacement for certain vintage transistors but there may be some others that could be put in the same spot and give good service. Based on some markthefixer lists I likely used the KSC2383 for the 2SC1318 since I can see some tall TO-92L types in my picture. KSC1845 is the go to for the 2SC1344 on the tone board. On a number of older vintage units the "low noise" NPN types used on the tone boards and the front end of some older amp circuits can turn noisy (hissy) as they age. Replacing them can sometimes dramatically lower the noise floor of the unit. The outhouse shaped Hitachi 2SC458 is probably the most notorious of the older types. Initially my SX-535 sounded like it had a head cold, lacking in the highs, even more so with the FM tuner. Basically sounded tired and worn out. After new electrolytic capacitors and transistors it sounded so much better.

 

[ChuckinNC]

There are other potential vintage transistors that can get noisy in the unit. There are the 2SC1318 on the amp card and there should be some 2SC1344 on the switch/control board (tone controls). The volume and balance pots (VR2 and VR1 in the schematic) are both upsteam of the 2SC1344s that should be on the control board so they would have no effect on noise from them. In some units the volume control is between the tone board and the amp board.

If something acts up as it warms up freeze spray can be used to chill transistors as the problem starts and if chilling them calms them down for a time then you have likely found a culprit. Have used that technique to ID a differential pair that were acting up doing a rat-a-tat-tat that were transistors that get little mention (likely uncommon - it was an old Sherwood). A can of canned air (duster) turned upside down may be usable as freeze spray, not sure about the issues using them that way. Probably a bit awkward. I have cans of Dust-Off looking up the msds sheets it is listed as being flammable.

Have had an amp that developed periodic bursts in the background and freeze spray did nothing but gently tapping on individual transistors with a hard plastic tuning tool caused the culprits to start making some really weird noises I would not expect transistors to make (out of the amp through the speakers). Replacing those two on the channel got rid of the issue. It was a cheap GW find Yamaha amp that had a blown driver transistor and after playing fine for a period after the original repairs the static burst issue on the same channel began. A pair of 2SA844.

Based on this old bad 11 transistor list I found years ago and saved a copy to my drive the 2SC1344 can develop a static burst issue.
View attachment 2026778
I think the SX-535 I picked up had 14 transistors of 5 types on this list in it. They were well represented on the amp card, tone board, phono circuit (equalizer board), and the last two on the tuner board. I obviously did not use the KSC2690 on mine. Often there is a commonly recommended replacement for certain vintage transistors but there may be some others that could be put in the same spot and give good service. Based on some markthefixer lists I likely used the KSC2383 for the 2SC1318 since I can see some tall TO-92L types in my picture. KSC1845 is the go to for the 2SC1344 on the tone board. On a number of older vintage units the "low noise" NPN types used on the tone boards and the front end of some older amp circuits can turn noisy (hissy) as they age. Replacing them can sometimes dramatically lower the noise floor of the unit. The outhouse shaped Hitachi 2SC458 is probably the most notorious of the older types. Initially my SX-535 sounded like it had a head cold, lacking in the highs, even more so with the FM tuner. Basically sounded tired and worn out. After new electrolytic capacitors and transistors it sounded so much better.

Thank you for all the suggestions and the background information. The bad transistor list confirms several that I have already replaced on the amplifier board.
I turned the receiver on this morning, and it performed pretty well. There was a very slight hissing sound on the right channel, but the audio performance was fine. I was pretty confident that these things don't spontaneously heal themselves, and about 15 minutes into my listening session all hell broke loose on the right channel. It was a static storm overlaid with intense popping noises. I turned it off as fast as possible to preserve my newly rebuilt Advent speaker. The static storm on the right speaker was there, even when I turned the balance knob all the way to the left speaker. The right channel will occasionally produce some faint audio, but it is mainly static and popping. I let it cool down, and tried again, but the popping and static were still there.
At this point, is it worth replacing the output transistors ? I think my problem may be on a board, other than the amplifier, since I have replaced the capacitors, diodes, and all the other transistors except the outputs. I am thinking the AWM-068 SW and control assembly with its 2SC1344 transistors from the suspect list would be a reasonable next step. Is there a way to get to these transistors easily ? I appreciate all the help. Hopefully I can figure this out. There are suspect transistors on the Equilizer board AWF-014 also. These look easier to get to. How do you remove the AWF-014 board that is held to the metal chassis with plastic plugs ? I think these will break easily if I don't do it properly?

 

[dly66]

The SX-535 was a few years ago, the SX-636 earlier this year. Basic construction similar. The boards on plastic standoffs you can pinch the top part together using needle nose pliers (be gentle, 45 year old plastic gets brittle) and pop each corner loose and slide the board up and pivot to work on. It may take some force to get the corner to pop free, relying on the judgement that will keep from breaking the standoff or cracking the board, how much force to apply along with where and how to pry.

With practice one should be able to solder with a board nearly vertical, the solder should wick into the joint.

The board with the tone controls where the 2SC1344 should reside you would need to take the top cover off (4 screws, 2 on each side), the bottom panel (many more), pull the knobs from the front panel don't remember Pioneer using any set screws on these. Front panel should be held with 2 screws on top and a few thin nuts with washers that were behind certain knobs. I believe bass, treble, and function. Should be able to pop it off then, don't believe there were any screws along the bottom edge. Then there should be some nuts and screws holding the pots and switches to an interior metal panel that was behind the face panel below the dial. Those fasteners will be right behind the face panel. Remove those, likely need to free some wires from the plastic retainers to allow more freedom of motion for the board. You should be able to work it out the bottom and be able to flip it back to get access to both sides. Can do a better job getting Deoxit etc into the pots and switches with the board out like that.

When working on it with the face off pay attention to the exposed tuner pointer and keep track of where it is so you don't catch anything on it. I believe it is acrylic so it can snap very easily. Got that lesson on the SX-535. Snapped it twice, clothing caught it. Have avoided snapping any pointers since then. Super glue bonded it back together. Had to apply some black RTV around the glue joint since it created a second red glow point there which was annoying. The RTV blocked the light radiating from the glue joint.

 

[dly66]

Notice you use ChuckinNC. North Carolina, Northern California, or NC represents something else?

 

[ChuckinNC]

The SX-535 was a few years ago, the SX-636 earlier this year. Basic construction similar. The boards on plastic standoffs you can pinch the top part together using needle nose pliers (be gentle, 45 year old plastic gets brittle) and pop each corner loose and slide the board up and pivot to work on. It may take some force to get the corner to pop free, relying on the judgement that will keep from breaking the standoff or cracking the board, how much force to apply along with where and how to pry.

With practice one should be able to solder with a board nearly vertical, the solder should wick into the joint.

The board with the tone controls where the 2SC1344 should reside you would need to take the top cover off (4 screws, 2 on each side), the bottom panel (many more), pull the knobs from the front panel don't remember Pioneer using any set screws on these. Front panel should be held with 2 screws on top and a few thin nuts with washers that were behind certain knobs. I believe bass, treble, and function. Should be able to pop it off then, don't believe there were any screws along the bottom edge. Then there should be some nuts and screws holding the pots and switches to an interior metal panel that was behind the face panel below the dial. Those fasteners will be right behind the face panel. Remove those, likely need to free some wires from the plastic retainers to allow more freedom of motion for the board. You should be able to work it out the bottom and be able to flip it back to get access to both sides. Can do a better job getting Deoxit etc into the pots and switches with the board out like that.

When working on it with the face off pay attention to the exposed tuner pointer and keep track of where it is so you don't catch anything on it. I believe it is acrylic so it can snap very easily. Got that lesson on the SX-535. Snapped it twice, clothing caught it. Have avoided snapping any pointers since then. Super glue bonded it back together. Had to apply some black RTV around the glue joint since it created a second red glow point there which was annoying. The RTV blocked the light radiating from the glue joint.

Thank you so much. Your advice and experience will give me confidence to keep going. I was not sure how to tackle the front panel, but your detailed instructions are appreciated. I would never have thought about the delicate tuner pointer getting caught. I am sure I would have snapped mine off. I played the receiver this afternoon, and the static storm and popping is very intermittent, and heaviest when first turned on. I played it for about 15 minutes, and it never came back, but there is still a faint static hiss from the right channel. I have some freeze spray coming next week that may help me isolate the problem.

 

[ChuckinNC]

Notice you use ChuckinNC. North Carolina, Northern California, or NC represents something else?

Chuck in North Carolina, actually. I never thought about the confusion with Northern California. I live just outside of Lenoir. Thanks again for the help and advice. This was the first piece of audio equipment I ever bought, and it was a financial stretch back in those days. I would guess I bought it around 1975, so it is 45 years old.

 

[ChuckinNC]

Here is an update on my SX-535. I still have the background hiss and occasional popping on the right channel after replacing the capacitors and transistors (except the outputs) on the right channel amplifier board AWH 035. I used Ben's kit from Ebay for the parts. ( five transistors and four capacitors, and two diodes) It is loudest when just turned on and seems to die away gradually, but never is silent. This is pretty much the way it was before my repair attempt. It is there even with the AUX selected, and the volume, bass, balance, and treble controls have no effect. I could live with this, as it sounds fine otherwise, and the background noise is very faint to my aged ears. Unfortunately, I get a very loud popping, static, and loud hum that sounds like amplifier feedback on occasion on the right channel after 5 to 10 minutes of operation. It doesn't blow any fuses, but I am concerned about harming my speaker. It lasts for 5 seconds or so, and then gradually fades back to the faint background hiss and static. I have tried freeze spray on the components, but can't isolate anything that seems to affect the background hiss. I did replace C22 Capacitor on the AWM 068 control board because it was sensitive to tapping on it. The replacement seems quiet to any tapping.
I did clean all the push buttons and controls several times with tuner spray as suggested. I do think that helped to lower the background static and hiss level. Thank you for all the help. Any ideas on what may be causing the intermittent loud right channel amplifier feedback would be appreciated. This is a new problem that arose after the work I did on the amplifier board. It seems like it wouldn't work at all if I had really messed up. Fortunately, the left channel remains static free.

 

[Binkman]

G'day; What transistor p/n's were included in this kit?

 

[ChuckinNC]

G'day; What transistor p/n's were included in this kit?

The original two A763 transistors were replaced with two new A992. The two original C1318 were replaced with C2383. The remaining A720 was replaced with a new A1013.
I did make myself a dim bulb tester. I was thinking that it might be instructive to power up the receiver through the dim bulb tester to see what happens when I get the loud amplifier feedback ? Could it be something shorting out ?

 

[ChuckinNC]

The SX-535 is back up and running well now. I thought I would reflect back to the original problem, and give my opinion on what solved my right channel noise. Replacing the transistors on the Amplifier Board was probably not necessary, as my board did not have the dreaded A726's. It was worth doing, but probably not the cause of my problem. If I was starting off from the beginning, I would first clean the potentiometer controls , and then clean them several more times and exercise all the buttons and knobs. Then I would replace all the electrolytic capacitors on the amplifier board. I would re-solder all the connections on the board while I was there. Then I would test it with a dim bulb tester before hooking it up to the speakers. If more work was needed, I would then look at the AWM-068 switch and control board . I found several touchy capacitors there (plenty of light blue ones). I wound up replacing C22 on the board, mainly because I could get to it easily, and I had a replacement. So far, things seem to be working well. The initial popping noise and static I got whenever I turned it on is gone. I plan to order all new capacitors for the switch and control board just in case I need to get back in there. I still need to replace the stereo indicator bulb and it will be done (for now). Thanks to everyone who offered help and advice along the way. I am grateful for those who created and maintain this web site. It really does sound nice with the Advent speakers I rebuilt a while ago.