Pioneer SX-950 power amplifier repair

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Post-repair performance check: • Pioneer SX-950 objecti...
The third or fourth repair of a Pioneer SX-950 receiver which has had a very long-running tradition of exploding.
The last failure was brought on by either a broken pad on the power amplifier board, or a bias potentiometer going open-circuit. The bias potentiometers were replaced right after the failure, but after that repair I put it on a shelf and let it sit for a year or two, dreading to fix it in case it was going to explode again.
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Опубликовано:

5 окт 2024

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Комментарии : 49

@taineasy 3 года назад

I purchased an sx-950 after getting out of college in 1977 and its still my daily use amplifier receiver for almost 45 years. I have never had any issues with it at all.

@FFcossag 3 года назад

Lucky. Mine keeps exploding.

@taineasy 3 года назад

@@FFcossag mine is 100% original and still has a DC offset under 5mv on both channels. Original lamp bulbs except one. Note: I have always run mine with the heavy wood cover off the unit just I do with my even older Heathkit AR1500A. I am not a fan of heavy wood cases as they create an oven effect.

@concernedpatriot9314 Год назад

I got mine in Spain PX in 1977 and repaired it 30 years ago but it need fixed again!

@robertkeefer7791 6 лет назад

Non-exploding electronics are definitely preferable! Nicely done.

@ProdigalPorcupine 8 лет назад

Nice amp! You just can't beat vintage gear for quality and sound IMO.

@FFcossag 8 лет назад

+ProdigalPorcupine That is often true - sadly, once I get the performance test video up, you'll find out that the performance of these old Pioneer boxes really isn't too spectacular. They definitely can't be beat for ambience, though, just given their sheer size and shine.

@ProdigalPorcupine 8 лет назад

+FFcossag Meh! You can prove anything with your fancy 'science' and 'specs'! ;-) There's a few crappy sounding old Japanese amps out there, but I've always been quite impressed with most of that era. I have a lovely early 80s Realistic STA 2080 receiver I should dig out and overhaul. 365UKP back in 1981! It's a thing of beauty.

@FFcossag 8 лет назад

ProdigalPorcupine I was referring specifically to these Pioneer receivers. Most Japanese hi-fi gear of the era was very well-performing by any standards.

@jmcgatkinson 8 лет назад

I'm interested in what Pioneer installed as power output transistors; 2SD... of some kind.. a complete test would incorporate the use of a dummy load across the speaker connections, and nominally 8 ohms. Send a signal (say, 1kHz sine wave) through to check voltage, and calculate output power at the point of 'clipping', and 'drive' it for a few minutes, and check for 'heat' on components (after switch-off).. Those older 'brushed aluminium' style front panels still have much appeal, so whenever I come across one I just 'fix it', and ask why later..!

@FFcossag 8 лет назад

If you're curious, I performed a more proper performance check on it soon after repairing it: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hpwgQLBTZUg.html The original output stage, I THINK, were 2SB/2SC transistors of some kind. It's in the SM if you really need to know, but it strikes me as a bit irrelevant today when you can get much better spec MJ series devices to fill in to gain some reliability.

@jmcgatkinson 8 лет назад

+FFcossag Yes, quite right with the MJ series, and their availability and specs. I sometimes make comments mid-process, and often find the 'next part' covered that ground already! My last job with the 'Pioneer' brand was the replacement of an IR remote sensor. Used one from a scrapped video. Took a long time to diagnose and repair; connected the (faulty) sensor to the oscilloscope, found an output (aiming the remote control at it, and pressing a button). I the tried the sensor from the video.. 10 times the amplitude... fitted it, and successful repair...

@dansibayo4214 5 лет назад

The board shows a lot of cold solder.

@geoepi321975 8 лет назад

one emitter resistor is different you should replace them all to balance it

@FFcossag 8 лет назад

+geoepi321975 It's different, but they're all within the specs of the original ones, so I just haven't bothered. The power amplifier portion also performs to spec, so it's just a cosmetic thing.

@MichaelBeeny 8 лет назад

When the music started I thought, oh no, still not fixed!! then I realized it;s just crap music!'' Sorry, just showing my age. As usual, enjoyed your video.

@FFcossag 8 лет назад

+Michael Beeny The music I use is weird, since I opt to only use 100 % public domain songs in my videos; since that does NOT include all the good CC-BY licensed songs you can find on the net, nor lots of classical music (the recorded performances are often copyrighted even though the music is not) my selection has been very limited. If you know of some good public domain tracks to use, I'd love to extend my collection.

@scotshabalam2432 7 лет назад

Maaaan, do yourself or some future repair tech a favor and replace those wire to PCB soldered connections with connectors. PCB will probably last longer too.

@saarike 7 лет назад

Nice repair!

@SinnerSince1962 5 лет назад

It's all fun until you let the smoke out!

@karimdailyjazz 5 лет назад

good job

@CerberusProject 8 лет назад

I have a Pioneer SX 5580 (The civilian clone model would be the Pioneer 1050) that I can't get any sound out of. It powers on just fine, knobs are real smooth, and I can get signal with antennas; but I get no sound out of any speaker port nor the headphone port. What might be wrong with it?

@mt2smooth 4 года назад

I have the SX-980 having hard time trying to find Power Knob for my Device. Wonder if you know and Website. Ebay puts me with the wrong Model Number. Thanks if you could help.

@ricardodolina8178 5 лет назад

Nice job. I enjoyed your video.I have a SX-850 to repair.Thanks !!!

@moigonli9834 3 года назад

Ricardo , where are you located?

@ricardodolina8178 3 года назад

@@moigonli9834 Buenos Aires

@zerno2348 8 лет назад

Hi, interesting video, but i have a question. Where are the measurement stripping of the multimeter at 9:40 connected? At capacitors? Can i not properly recognized. Greetings from Germany!

@FFcossag 8 лет назад

+Zerno It's connected between the positive and negative wire-wrap terminals of the amplifier module. Keep in mind that I incorrectly state that I'm measuring one voltage rail; I'm actually measuring across both.

@zerno2348 8 лет назад

Ja vielen dank für die info. da ich nicht so gut alles in englisch verstehe, ist es schwierig gleich alles zu erfassen. Ich sehe dann anhand der videos was sie machen und kann es mir herleiten. nur die anschlüsse habe ich nicht genau gesehen, wo das angeschlossen war. vielleicht können sie bei zukünftigen videos mal kurz reinschwenken, das man sich ein bild machen kann wie sie angeschlossen haben und wo. ich lerne gerne dazu, da ich mich dafür interessiere und es als hobby betreibe. ich möchte mir auch in zukunft ein oszilloskop kaufen und da sind solche videos von ihnen und anderen "kollegen" wie 12voltvids sehr hilfreich und informativ. Liebe Grüße!

@FFcossag 8 лет назад

+Zerno I don't speak German, and I don't dare say anything based on Google Translate, I'm sorry.

@jcamp3606 5 лет назад

Subscribed!. I need you help. I replaced the bias and dc offset pots but I need to know a good starting resistance point for them as the original pots we're completely toast and I don't have a reference . Thank you

@FFcossag 5 лет назад

I think the service manual has a procedure for that. The DC offset pots don't really matter since you won't blow anything, but the bias pots should generally be turned to their minimum bias level before first start. You can't usually turn it down too low.

@jcamp3606 5 лет назад

@@FFcossag Thank you so much for the reply! By lowest level do you mean closed 0 ohms?

@jcamp3606 5 лет назад

@@FFcossag also the pots I got are 0.2w rated. Should I get bigger ones? Thanks

@jcamp3606 5 лет назад

@@FFcossag Another issue I am having is I get -50v through the bias pots from ground on powerup then after a second flattens to 0. This is with no power transistors connected. I am also getting 50/-50v between collector, emitter and base.

@jcamp3606 5 лет назад

@@FFcossag Its alive! and all good :)

@ih8myfriends 6 лет назад

Might you know where one might find the schematics for this amp?

@FFcossag 6 лет назад

They're probably on hifiengine.

@steaker-gi9uw 8 лет назад

what's with the spooky music?

@FFcossag 8 лет назад

+steaker1705 I only use public domain music in my videos, and that limits my choices a bit.

@tony1103 8 лет назад

can you fix mine? i'd pay to have it fixed,

@FFcossag 8 лет назад

Unless you also live on Åland, then no. Shipping would be thousands of dollars.

@TonysVault 7 лет назад

+mdenny9969 Long Island but I can come down there.

@TonysVault 7 лет назад

+mdenny9969 the audio goes in and out.

@tsd71 4 года назад

The sloppiest work I've seen in a long time

@peterfolchi1032 8 лет назад

I was the 12th view yay. Nice amp btw.

@CPUTests 8 лет назад

Are you testing that amp with no load??? Are you aware that you could kill the outputs and even the drivers doing that? You must have at least a 8 ohm resistor instead of a speaker or even a speaker connected or you risk to burn the amp even with low volume or no volume at all. My god! Do you know what you're doing??? I don't beleive so...

@FFcossag 8 лет назад

+CPUTests This is not true for any half-modern transistor audio amplifier. Some of the really early (think 60's) transistor amplifiers built before they really mastered negative feedback could oscillate and explode if you disconnected the speakers, and transformer coupled tube amps should certainly not be run without load. A "modern" amp like this, though, being built to act as a voltage source, really couldn't care less. Which makes sense, since else it would explode if you were to turn the speaker outputs off with the buttons on the front panel.

@cocusar 8 лет назад

+CPUTests It's not nice to say that other people doesn't know what they're doing, specially when you really don't have a clue of this kind of electronics. Btw, I'm an electronic technician and in my last year of engineering, so, I can guarantee that what he is doing is fine.