Diagnosing a Pioneer SX-535: High DC Voltage at Speaker Terminals!
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- Опубликовано: 11 мар 2021
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This SX-535 had extremely high DC voltage at its speaker terminals. The source of the issue was the power amplifier board. I thought at first it might be the differential pair transistors, but it was actually the bias transistors that were causing the issues. Replacing the old 2SC1318's with modern KSC2690's solved the problem! I had seen very similar things happen with the Pioneer SX-636 in the past, which has a very similar power amplifier design.
A liitle post-fix suggestion ... cheak the solder on that power amp board. I will generally heat and reflow anything in the bias or output chain, just to be sure we aren't being fooled by broken solder.
Cyrrently repairing a Rotel 1075 with DC on 2 channels. This video has been very helpful.
I had the 636 growing up in central america in the late 80's. It also had this same problem with DC voltage and also making a loud scratching sound in one channel. Being a kid at the time, I had no idea what the problem was, but luckily there were a ton of repair places locally and they charged a kid-friendly $30 to fix it for me.
Kudos for quickly finding the issue with this receiver. I commend your direction on this problem and getting it fixed with efficiency. There is something to be said with practical experience and find we are always learning as we go. With that said, for your reference Q5 and Q6 (the 2sc1318 transistors you replaced to solve the issue ) are not bias transistors.. This amp topology is a full complimentary push pull design using direct coupled stages and has no output coupling (OCL) whatsoever hence why it has a differential stage with dc stabilizing feedback. Each channel uses a single ended simple Pre-drive class A gain/constant current source device direct coupled from the differential stage to the driver stage which are the transistors you found faulty. The variable resistor and stacked diode (thermally coupled to the heatsink) array is your bias circuit as well as the path for the positive signal and current source. The transistor you replaced is in turn not a bias transistor at all. These lower power units did not incorporate any transistors in the bias circuit. Also Bias failures do not lead to high DC voltage as much as it would lead to over current situation of the output devices being turned on too long between the complimentary pairs. What was likely happening is that these matsushita transistors were intermittently breaking down and you were losing your pre-drive/constant current source and since this device directly coupled at this point to the PNP drive, the circuit went into saturation on the negative drive side and was just pumping a large negative voltage as a result. ( note in your video it was -14VDC)
Thank you so much! I started playing around with what you are doing about twelve years ago. I had “0” experience with electronics, but watched years, literally, of videos I could find on the internet, describing the process. Obviously, I love vintage gear!😎 Someone took the liberties of breaking into my home, some years ago, and thought that all of my repair equipment, including about $1500.00 worth of capacitors, resistors, ...blah, blah, blah.... that I had researched and sought out, painstakingly, for months, and thought they belonged to them!
I digress!
I am slowly coming back and I am living once again, vicariously through you. I enjoy your videos very much and want to say thanks!
Now I am slowly building my stock back and watching studiously. Please don’t stop!
A Fan!
Thanks,
Rick
I've been burglarized as well. Several times. Keep moving forward. Stay well.
Nice detective work. Backward tracing and the process of eliminations did the trick!
When you know what you're doing, looks so easy !!! Thanks I am learning, you're an outstanding troubleshooter !
Hey I picked up a non working SX-535 with no sound in one channel. Following you video, I changed both pairs of differential transistors, and presto the amplifier works great. Sounds good too. Really easy to dial in the bias. DC at the speaker terminals is low too, 2mV and 5mV. Thanks so much for your video !
After military service and broke in 1975, the hifi bug bit me. I wanted this Pioneer SX-535 but had to settle for the 434. I really dug the blue back-lit dial scale, orange station pointer, red STEREO lamp and basic controls. That SX-434 was boss.
Offering two tape loops, twin tuning meters, Aux and Mic inputs on a 20wpc receiver was rare and made this 535 an exceptional bargain. I use a resurrected SX-434 in my kitchen hifi system powering a Nakamichi BX-1 cassette deck and Synergistics S12B and Boston Acoustics A-40 speakers. Even these "cheap" Pioneer receivers could drive 4 ohm loads. Swell video.
Thank you for serving!
@@FortyTwoAnswerToEverything- well I got drafted so I didn't have much choice. Very kind of you to say thanks, it means a lot to me. So few people ever say it.
An added bench test equipment is a signal generator plus and and let's not forget high wattage resistors between 8 and 4 ohm will save speakers from being roasted.
I have encountered noisy transistors that have black oxidation on the leads. I clean that off and take a sewing needle and scrape between the pins under the body of the transistor try that sometime. If its still noisy replace. I'm sure everyone knows about trapped moisture under glue that corrodes and causes noise. I recently fixed an Akai amp that had conductive glue on it by scraping the glue off
Great series of videos. I hope someone with my limited electronic experience can complete my repairs!
Thanks for another nice and easy to follow video that was well put together.
This is really good. Very straight forward and not overly technical.
Genius. Nice demonstration.
Nice job man... pretty series of receivers .. working on my 737 project on and off between work and ordering parts. It'c doing great so far. Thanks you for all the tips , great channel you have created !
excellent quality base bro
Just now subscribed, have watched quite a few of your vids and really Liked, GoodUp
a beer!!! and I thought I got a deal at $10!!
Love your video :)) It made me understand what could be wrong with an amp that I have that doesn't come on. The relais does not switch on and it shoots in protection mode. It seemed that it also has a high DC on the speaker terminals but I am not sure. I am trying to fix it for over a much too long of a period now and really want it done :) It's a Hitachi HMA-8500 mk2. Now for the search of the transistors on it. Thank you for inspiring, I love your explanation in your vid.
Great video considering that I have an sx 636 coming on May.Now I know some of the problems it might have specially with those transistors you mentioned.Thank you.
Definitely. The 2SC1451's on the 636 amp board absolutely must be replaced with KSC3503 for it to be reliable and not kill your speakers!
@@AHFixIt thanks for the guidance!!
Pretty impressive for "limited experience". I wish I knew half of what you do. But hey, I'm learning.
Good video, but you may have confused people when you described how you identified this receiver as being a direct coupled(DC) receiver. You pointed to the filter capacitors in the power supply, these capacitors have nothing to do with the amplifier being DC coupled or not. What you should look for in determining whether an amp is DC coupled or not is whether it has coupling capacitors or transformers in the output stage?
Watch it , you'll let the smoke out !!! , Always check capacitors first on an amp this old . Old caps go bad !!!
Old caps go bad? Wow, no one has ever heard of that!!! ;)
It looks like that can of beer paid off! That was a great video. I bought a Marantz 2230 a few days ago and it should be arriving at my house I think next Wednesday. Everything works, all the lights work and it is near mint. At least that’s what the seller claims and I have been pretty lucky on eBay with receivers so, I will let you know if I made a good deal or not. Got it for $600.
Hey I watched your video,and just fixed myown SX535 with the same transistor! I used NTE 289A
I have that transistor tester too, mostly use it to just check pin outs because it does provide enough voltage and current. Plus I dont think it would detect noisy transistors either.
2SA763 are PNP devices, and are a common failure point. Many of the PNP devices used in vintage audio as differential input devices fail causing DC offset.
Great job!’
Very...informing! I have a Pioneer SX 1010 I just had totally rebuilt. Everything(so-to-speak)inside has been replaced.
Don't abuse those dynacos. Get some less worthy speakers to test with.
If you still use them you might gain some bench area by mounting them on the wall. They have mounting brackets on the back.
I like your site.
Gunky bias adjustment trim pot? Cleared itself with heat and jostling?
Probably was cold solder joints, when you changed out the transistors it reflowed with new solder. May save some time with future repairs.
Just wondering, did the transistors matched that you pulled from the unit?
New to your channel and I'm enjoying the content. Nice explanation on troubleshooting, thank you.
Did you get a reply? I'm about to re solder some cold joints
@@CM-dw3gh No, you are the first.
@@daledickey8400 always the way. Hope you got it sorted
Good diagnosis. I'm recapping my JVC jrs401, and the bias transistors are on the list of "10 known bad". The replacement is difficult/expensive to find, so going to make extra effort to replace. On this unit the matched transistor set is a combined set of two. Cannot find a replacement anywhere. Xraytony uses thermal epoxy to glue two together. Think I'll wait on that. Keep up with the great vids.
Why would they have to be physically glued together? That makes little sense to me.
@@foobarmaximus3506 Heat transfer, so the transistors thermally track the same.
thank you
Wondering how to take the case off....so I can work on my old stereo. There are so many screws I don't want to take them all out if I don't have to. Thank you
Nice!
I wonder if u can help me with this one with the same issue.
I have a teac stereo receiver radio/twin auto reverse cassette deck built in,,,and a seperate turntable and cd player that connects to it.
The problem is the stereo itself,,,,when u press the power button to go into standby,,,,,it makes a loud hum noise thru both speakers,,,,as if there,s high voltage going thru them,,,causing damage to the speakers.
Strange thing is when the stereo is turned on,,,,it sounds great,,,,loud and clear as it should b,,,,thru the speakers,,,,on all inputs.
The stereo does have a relay switch on the low voltage side of the power supply transformer,,,which does click when u turn the power on and off on the receiver,,,,or the remote control.
What would b the cause there of the hum noise thru speakers,,,,in standby mode? Could it b the filter capacitors on the power supply board,,,amplifier board,,,etc?
Thanks a lot for the video, I have a Pioneer SX-535 and its tuner does not work stereo, do you know the problem?
Consider that, AH-fixed. Nice job.
Had the legs of the transistors adopted a black tarnish? Sometimes this tarnish (if present) can be enough to mess with the switching of that transistor, also it is possible you have a dry joint somewhere, often on the legs of the bias resistors as they tend to be chunky and require extra heat when soldering, also they vary in temp causing dry joints, it's possible that something like this was uninventively fixed as you were doing other work.
Does this amp have variable potentiometers for the bias? Often these become tarnished and need replacing or a good clean, if they are tarnished or sometimes damaged from a blown power transistor they can send the bias crazy.
14 volts DC across the output. How about the 60 volts DC a Crown DC300 can put across its output when one of the output transistors is blown?
Would freezing the transistors with spray not shown up the problem. Kind regards.
there is a speaker dc protect board you can buy as a kit.
I just got the little brother to yours. Its the ST 434 at 15 wpc. It works and the controls are not scratchy but it sounds like its clipping and fuzzy when playing music at medium volume. I measured the bias dc offset after warm up and it was about 12 mv so good. What could the clipping fuzziness be from?
You came out very well.on that deal! The guy that swapped with you for a stupid beer is an idiot!
With your experience with that particular receiver what would be the main cause of a weak sound on the left channel?
Nice work but just to be clear, Q5 and Q6 are not "bias transistors". This model uses bias diodes D3,4,5 and D6. The transistor you replaced fixed it, just mentioning. AudioKarma is like a cheat code for common fixes, but they are not a definitive source.
true...
His problem is he doesn't know how the circuit works! If transistors Q5 or Q6 are not conducting current properly,the output terminals will swing positive. If they are conducting too much,the output will swing negative. If the emitter-base is open,then the output will swing to the positive rail. If it is shorted emitter to collector,then it will swing to the negative rail.
Both channels had a very high dc offset, then it went away. The transistors were no the problem. Both channels did not fail identically via two discrete transistors.
@@foobarmaximus3506 So what do you think the issue actually was?
The driver transistors are part of the bias mechanics, that is why he refer to them as the bias transistors.
The drivers are connected to the base of the pnp and to the cathode of one of the 2 bias diodes.
This will definitely help! Could you post the link to the transistor replacement numbers. One the hardest things for me is knowing the correct transistor.
audiokarma.org/forums/index.php?threads/transistor-substitutions.688515/
Having problems troubleshooting my thrift store buy. Worked great for a while, then I moved around and it might have been bonked a time or two and now it's weird. Everything on the board looks great and nothing stands out as broken or bad. I'm trying to test certain things to rule out what is the problem, do you know of a good place to find information on what voltages, resistances, and continuities I should get? Just trying to figure out if getting 14mV on one channel and one channel going from 0mV to 5mV and back and forth is normal or not.
No VDC coming from speaker terminals but if you have any advice on tracing an issue with no sound from L channel A/B/Phono/Aux I'd greatly appreciate some help. TIA!
You should have car washed it first! LOL Just kidding. Great work as always.
hello iwant help repair my pioneer stereo amplifier A-6 bad dc to coming in effect audio is 38volt in band
What could cause lighter DC voltage (250mv- 350mv) on all five channels of a B&K Components power amp? Even in standby (via 12v trigger from preamp) mode, or when the amp is on with nothing connected. The only connection between all channels is star ground. Could a leaky transistor pollute ground causing this problem? High DC voltage on one channel is typically an easy fix, but I don't really know where to start with this rare problem. One day I noticed a hissing sound coming from all speakers and I measured about 1/3V on all five outputs. If you can give me any advice it would be much appreciated, because I can't find anything remotely close to my problem on Google.
So you say you replaced the differential pairs with the KSA992. I have a question tho, do you replace the 4 transistors with the KSA99A? or there is a PNP and a NPN that comprise each pair?
About the transistors you removed tested OK, could it be a leakage that caused the problem but not detected by the tester?
Great video !! I’m just getting into refurbishing my marantz 2250b and I’m looking for a decent quality multimeter and solder station . Can you tell me what you use or would recommend if you were purchasing these items today ?
Thanks in advance and loved all your videos to date 👍🏼
You've given me an idea for a future video! Honestly, any multimeter with a diode function should be just fine. I used a $40 one for years before I upgraded to a Fluke 117, which is still overkill for this stuff. Soldering station, anything that has an adjustable temperature control should be fine. I'm using an ancient Weller that I inherited years ago where you have to swap out tips to change the temperature, so I'll probably upgrade soon. Weller and Hakko are good brands. Solder sucker I use a Hakko FR-300. For someone just getting into it, a $10 spring-loaded solder sucker works great.
@@AHFixIt haha thanks great info and yes definitely worthy of a video just of general minimal tools needed to “start “ getting into refurbishing old gear . Also since we are brain storming video ideas maybe tips about parts sourcing and which sites are your goto . Also maybe a mention to any forums online you might frequent to get answers from helpful people that don’t mind answering beginners issues 😉 also do you have an email for your channel if I’d ever like to ask you anything direct ? Thanks again 👍🏼
@@michaelmalodrums9674 Yes it is in the "about" section of the channel
@@AHFixIt right on thanks 🙏🏻
I just purchased the Hakko 888D, and the 301 sucker. Both are amazing! I've been soldering for 50yrs, and never knew how bad a regular unregulated solder pencil was. The station has improved my solder joints tremendously. Both seem to be built for the long run. The sucker is light years ahead of any bulb tool that most always caused frustration. What helped my decision to purchase, was seeing Hakko equipment in just about any audio repair video that I watch.
Probably blown outputs never a good thing bad design if the fuses didn't blow but hey pioneer has had a few of those. Seen many blown Pioneers with no blown fuses
Great info! just subscribed. have a question - my SX 750 - unrestored - works great except I have recently lost FM sensitivity in the tuner. Used to get 10 strong signals with Stereo light lit - now only get 2 weak ones with no stereo light. FM muting is off, same antenna as before.. What would cause a loss of reception like this?
Unfortunately I'm not sure. Tuners can be very difficult to diagnose!
Turns out I was wrong about the same antenna. Turns out a new digital antenna was installed without my knowledge. That appeared to be the problem. Apparently some digital antennas dont pick up FM radio! I got some old rabbit ears and am getting a good signal on stations. Good to know the units ok. Had an Sx 650 in 76 and got the 750 last year off Ebay. I've been lucky - no problems yet.. It sounds like i remember the 650 - warmer than modern units.I bought and tried 70s and 80s NAD, Technics,Harmon kardon and even a 1000 Speker craft from 2000. None had the rich, clean sound of the Old SX _50 series. The NAD 3030 was nice, and would be my 2nd choice.
cool
Very unusual to fail two push-pull transistor pairs on different channels in the exactly the same way. I think. Unless they're in the same IC package.
Could you do a video more into transistors? How to measure them / how to ID them all that jazz. Not a lot of good info out there and would love to hear your thoughts.
Not a bad idea! I'll add that to the ideas list.
My lamps in my 535 weren’t not working, I changed out the lamps with LED. They still are not working but the red stereo light comes on. Any suggestions?
Check the fuses on the power supply board.
@@AHFixIt thank you so much that was the issue. Awesome
What was that jazz piece that you played for test purposes?
Yes
@@AHFixIt Let me rephrase my question. What was the name of it and who performed it? I liked it.
@@bikdav it is called walk through the park by tracktribe! It is a royalty free tune that youtube listed for me as a creator and I use it in a lot of my videos due to its better than average recording quality.
At the 2:00 mark of this video, you said that 535's do not have a protection circuit in them. I have a Pioneer SX-780 and an SX-535 and when i power that 780 on, i hear a "click" about 2 seconds later and I'm assuming thats the protection relay being energized. So my question to you is, can a protection circuit be easily added to units like this that have no protection circuits? Thanks bro, love your videos!
Not easily. Anything is possible, though!
There are kits for adding them.
they sold alot of those!!!
Why wouldn’t a person just buy Emotiva? No static no scratches no service calls 3 year warranty
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Safety glasses for a simple soldering job at home ? its soldering not welding.