Pioneer SX-X3X Preventative Maintenance: 2SC1451 Transistor And Differential Pairs

Need tools? Here's a video showing what I use (with links!): • Must-Have Tools For Wo...
Everyone has heard that it's good to "recap" a receiver, or replace all of the electrolytic capacitors. Yeah, that's good, but not often do people talk about "re-transistoring" a receiver. No, you don't replace every transistor, but in these vintage receivers, there's always a transistor or two that's known to fail. In these mid 70s Pioneer receivers, the 2SC1451, often used as a bias transistor on power amps, is known to fail. Anytime you're working on one of these, it's a good idea to replace it with a KSC3503 transistor. And while you're at it, you might as well replace the differential pairs with KSA992 because the 2SA726's can fail as well.
EchoWars transistor testing: audiokarma.org/forums/index.p...
Applies to SX-434, SX-535, SX-636, SX-737, SX-838, SX-939, and SX-1010

[@Mrsteve4761]

I use a laser pointer to illuminate the component to replace on one side of the board while looking for the spot beam on the other. Makes identifying solder points easy to locate on the PCB. I use one intended to play with cats. Great video!

[@everythingreviewsandnews1229]

That sir is a great idea

[@bugsyjonesband]

Damn -Now I need a laser pointer. High brightness? anything specific you can recommend

[@williamwong5627]

U

[@Earcandy73]

A great way to see the solder joint locations is to shine a bright light on the component side of the board, you can then see the silhouettes of the components on the solder side.

[@stevefoster2700]

Exact problem with my 636. Started with the diff pair then the drivers, then finally the 2SC1451. Wish I had of watched this first 🤣

[@AmishSpecialForces]

I've always had great luck enlarging the holes on a pcb with small drill bits used for carburetor work. Using a hand-held driver, of course.

[@McCullochMac6]

Your Awesome....Thanks for the time you put into explaining these things...

[@mjg263]

MarktheFixer, echowars and the late merlynski (r.i.p.) among others in the Pioneer forum are such a huge help to all of us AK’ers! There’s just no place like AK, been hanging out there since shortly after they started. Great job and another awesome vid!

[@TorontoJon]

Amazing video and my hat goes off to geniuses like you that can fix these gorgeous vintage receivers. All the best! :)

[@MichaelYates]

Thanks for another informative video, good point about the matched pairs. I forgot to include that important point in my video.

[@insolentstickleback3266]

I learn something new every video, Thank You!

[@jackgabbert3233]

Hi, I recently found your channel and want to say big time THANKS. I'm trying to learn and among the YT poster's currently out there your content is some of the most helpful. Kudos to you!!! Regards, Jack

[@tobyerixon8827]

You´re very good at explaining what you´re doing. Hats off for you sir. 😀 And i love your Volvo. 👍😊

[@jamester1ful]

Excellent as always, learned a few things. Thanks

[@CoreyStevensBlues]

This is my exact problem with my SX-636. Thank you!

[@batforjustice]

I would not trust one of those transistor checkers without a second and third opinion. Micronta back in the day made a really good one that I still use. It puts it in an active circuit. Testing for opens or shorts is a start. Hfe is good to know when matching equivalents. But it won't give you the big picture. A battery powered scope works good for testing active junctions to. My eyes thought they saw some failing solder joints by those heatsink mounted transistors. At 12:54

[@BODEMAN85]

Excellent video I'm currently having similar issues with my SX-939, will definitely check this out.

[@user-jp7ms1zt7r]

My Dad's SX-737 has always been my reference against which I gauge audio equipment's look and feel. They're 50 years old, though, so I'm not sure I'd want to deal with the expense of the maintenance and repairs needed to keep one working well. I envy those of you with the skill set to work on those old receivers.

[@g.fortin3228]

these parts are all quite cheap. it's well worth it.

[@user-jp7ms1zt7r]

@@g.fortin3228 I don't have the technical knowledge for anything beyond very basic electronics, so I'd also be paying a qualified repair shop to do the work. The labor certainly isn't cheap. At this point, I want something with more modern features and more compact, but with build quality closer to that vintage gear.

[@sportsmemo7334]

Fantastic video as always. Very informative. I have an SX 737 that pops and cracks at all volume levels and inputs. While your video is incredible, I don't have the practice or the tools to do this with my 737. Can I just send it to you? LOL

[@Blowncapacitor84]

Just sat down for lunch!... perfect timing sir.

[@jtrobbins67]

Same here. Haha

[@AHFixIt]

Me three! Lol. I try to have new videos drop every Friday at noon Eastern time

[@Blowncapacitor84]

@@AHFixIt Nice! Definitely something to look forward to. Love the content man!!!

[@jeffberwick]

Good video as always. Really enjoy this channel. I'm thinking that the spike you saw while adjusting DC offset might have been due to a dirty trim pot. I cleaned the pots on my Marantz 2325 while adjusting offset recently and it seemed smoother and easier to adjust afterwards.

[@biggstile]

I appreciate your knowledge sharing

[@briang.7206]

Good work..I see eye protection that's important.

[@21anthem12]

Nice job. It would be nice to know the variant of transistors used. They’re available in multiple versions of hfe as denoted by different suffixes.

[@everythingreviewsandnews1229]

Just wow. Definitely not plug and play. I never even thought that the transistors had leads in a different pin out. that would be bad. :)

[@g.fortin3228]

Really appreciate this one. Just about to service/update semiconductors and PS caps (and some others) in my dad's 737. It really does have a nice build quality to it ! Is it worth doing warm white LED upgrade if nothing is burnt out yet ? or just open it back up when it happens. I'm sorta on the fence with that.

[@foobarmaximus3506]

That EBC stuff doesn't matter. LOLOL I had a relative tell me that one time long ago when I was working on a radio. I am not joking. Haha!

[@ryandrom7094]

Thanks for the great video! What would you do if you replaced the transistors and all of the sudden had 0v when checking the amp bias?

[@PhuckHue2]

Nice

[@JonPaul]

ya Markthefixer helped me with a SA-8100 - I guess he's helped repair 1.34 billion pioneer units by now. He's like the Pioneer Repair God.

[@AHFixIt]

He should make a KZbin channel

[@ronaldfriedline9297]

Yeah I have an sx-939 that just developed a noise floor. Humming and left channel fading in and out

[@seafordvalley]

Hi I have a pioneer SX 737 that goes into protection but there is no DC at the E meter resistors I replaced all of the transistors on the amp board and protection board with the ones you recommended also recapped the amp and protection board I even replaced the protection relay with a new one from digit key all of the voltages on the power supply are correct,but yet it still goes into protection any ideas why this might be happening I’d love to hear your opinion love your channel thanks Danny

[@GF-ok5yn]

Thanks for this great video. I replaced these parts this morning but unfortunately my SX-737 relay still turned off the unit after about 10 minutes of use. I suspect once it cools off it will work again. Just wondering what my next step might be to get the receiver in working condition. Should I replace components in the protection circuit or power unit. Any suggestion would be appreciated. Maybe I should go after the same transistors used in other parts of the receiver. I was listening to the FM station when this problem occurred, maybe I should see if the problem occurs when listening to the turntable. Thanks

[@GF-ok5yn]

Just to follow up, I did replace more components on the protection circuit and power board and now it is working well. Keep up the great content.

[@burner8959]

Hey man, fellow PA resident here, I've seen your KLH 17's in more than a few of your videos and I was wondering if you've had to re-foam the surrounds on the woofers? I've had a pair for over a year now that needs new surrounds and I couldn't find any info on YT about them. Basically I was wondering if you knew of anyone selling a kit for it. I recently found your channel and really enjoyed the rebuild of your Maggies. Keep the vids coming and thanks for any info you might have on the KLH 17s

[@AHFixIt]

The surrounds on my 17's are fully intact. Any generic butyl rubber woofer surround kit should get the job done, though.

[@g.fortin3228]

One question... on the 3503 replacements, do you have to measure a bunch and match pairs there too?? I'm starting work on mine .. your vid helps me a lot thank you !

[@AHFixIt]

Nope just replace it

[@g.fortin3228]

@@AHFixIt Thank you man !

[@Domdoesstuff58]

Hi! I have a fairly mint Pioneer SA-9900. I was looking at the schematic and it seems like there are 18X 2SC1451’s scattered throughout the amp. Do you think it would be worth the time and effort to replace them all? There’s also a PNP transistor with a very similar package, should I look into that too? I have a SX-737 to practice on first too.

[@AHFixIt]

Hi, great question. To answer your question, if the amp is working as it should, no. I say this because the SA-9900 has a protection relay - and so does the SX-737. If these transistors were to get noisy and send nasty DC to the speakers, the protection relay is there to help you. Now, if and when you start to see issues from these amps and you need to work on them, go ahead and replace all of the 2SC1451's, including the 2SA726's and other similar transistors that might be there too. This is a completely different story for owners of Pioneer stuff without a protection circuit, like the SX-636 and SX-535. Anybody who owns these should get this taken care of as soon as possible because they will cook speakers. I've seen it happen. But like I said, since you have protection in your amps, you're ok! I did this repair on the SX-737 in this video because I was already inside of it replacing components. There were not issues with the power amp at that time, but it was definitely worth my time to get this taken care of while it was on the bench with the covers off.

[@jeremygrb]

Hi everyone, the KSC3503ESTU seems to be no longer available(mouser and digi-key) . Does anyone know of another good replacement for the 2SC1451? I'm working on a SX-1010

[@markwhitfield5351]

Did you Adjust the DC offset first or the Bias? Is there a proper sequence to follow when aligning these?

[@AHFixIt]

I just do what the service manual says. I'm not entirely sure it matters though.

[@seafordvalley]

Hi I am working on a pioneer sx737. It is going into protection, no DC at the emitter resistors. I have replace all transistors on the amp board, also all caps on the amp board. I subbed them out with all the ones you recommended. Also rebuilt the protection board, the same way all transistors and caps. All voltages on the power supply are spot on. Also replaced the protection relay. Better than it was, it will play with volume at 9 to 10 o’clock. Put loudness on or move volume a little more goes into protection. Lower the volume comes right back on. Any ideas on what might be going on? Thanks and you have a great you tube channel, thanks Danny

[@gorak9000]

Did you check that the DC offset is 0 after you subbed in different parts?

[@justinplaysguitar]

Did it work. Did you fix it. I have the same thing going on

[@craigshupe]

Hello If you get time i have a pioneer that needs work. Maybe ship to you. It has some problems maybe you can fix? Thanks Craig

[@Silent-Lucidity]

I often hear technicians say they don't work on "chip" based audio. Like the Pioneer SX-60 (from 1983). Have you done any work with them or would you work on such equipment?

[@AHFixIt]

The closest thing to 80s gear I've worked on is a Kenwood KR-1000, and I was not able to fix part of it due to a chip that ran the speaker switches. 70s stuff can almost always be fixed.

[@Silent-Lucidity]

@@AHFixIt makes sense sir. I'm going to recap my SX-60. And fix a few button issues. ...after I test for DC on the output. Lol! :) I haven't looked at the circuit, and maybe that's micro chip controlled too! All I know is that the AM/FM tuner board takes up 50% of the space. And everything is separated far apart...very odd!

[@user-xm6qb5cg4i]

2sc869 2SC1451 problems in the protection circuit

[@foobarmaximus3506]

The hFe is only one part of matching the Qs. As you now know.

[@marcdich9066]

im sure youve seen me message on a few of your other videos however im just currious if u know were i can get used or remanufactured part for a marantz sr6000 ? i need the amplifier board, i think your not to far from me i could be wrong

[@AHFixIt]

I do not know, sorry.

[@PrimeHiFi]

Hey man you have discord? I run a server with a bunch of younger techs in it. Would be cool to have you!

[@mat.b.]

my amp has 2SC1451s...uhoh

[@tubeDude48]

Replace 2SA726 with KSA992

[@len9518]

No such thing as dc current. There is dc, there is direct current, there is dc voltage. dc current would be direct current current, which is wrong. Lots of knowledgeable folks say this, It's simply bad terminology. OK, I'm being picky. I'm a satisfied subscriber.

[@curtchase3730]

Like an ATM "machine". Should be AT Machine. how many ppl say that? I know yer being picky.

[@JM800]

How about calling it just direct current or direct voltage? Alternating current or alternating voltage? Alternating current voltage is rather strange also. Assuming that if the voltage is alternating, so is the current.

[@richardnalisnick462]

Only real Qualty audio used tubes not noisy transistors or scrappy electrolitcs! Sand is best left a the beacn!

[@garygranato9164]

forget pioneer , try rotel (a superior brand)

[@RaulHernandez-lg5nw]

The 2SC1451 does NOT set the bias current to the output transistors! It's used drive the output circuit!! You don't understand how the 2SC1451 works in the circuit!! You are misinforming persons that don't know transistor circuit theory!!!