0:15 Intro 2:21 Tony rant 3:27 Results of initial test - repairs needed 7:06 Troubleshooting results - first problem found, additional problems exist 12:03 Feeding signal directly into power amp to isolate problem to either the power amp or preamp section 14:22 Testing & repairing the volume pot 21:07 Flat amp board reassembled 21:15 Example of Hfe range color dot code on small transistors (They were replaced with KSA992 transistors with same spec) 22:42 Testing to see if the problem is repaired 24:49 Capacitor talk - Orange capacitors are all bad on this board! 27:55 Notes on protect/speaker relay 34:31 Should we ALWAYS replace electrolytic capacitors with film capacitors? 41:19 Closing comments
Hi Tony, I've got a slightly random question for you if that's okay. I've got a Sansui 6060 that has right channel issues, but I've noticed that the leads on most of the components are so black with tarnish that I can't get any readings from them. My question is, how would you go about resolving that? Would you clean the component leads somehow, (possible after removing them from the boards) and if so, how would you clean them or would you just replace them all?
Hi Tony, great video(s). Been watching, just wish that when you say "I've done that in another video", you'd tell us which one it is so we can go and watch it. 🙃. Thanks for being a great teacher and your humble approach toward us learners.
Great vid as always Tony! Bought a SX980 back in 1978, as an 'upgrade' from my beloved SX434. This video makes me really appreciate the incredible engineering and assembly that went into these. As an eighteen year old budding audiophile at the time, I sure didn't realize what an amazing piece of audio technology I had in my hands. Can't wait for the next installment!
Tony I appreciate that your instructing a wide audience, I prefer getting a better insight as to your knowledge of troubleshooting and schematic diagnosis. Don't get me wrong I enjoy your solder talk too
My first “serious” receiver was a Pioneer SX-626. The SX-980 was my second receiver. I gave it to a friend when I had to downsize my system. Great receiver!
The input coupling capacitor was done to save $. That's it. The increased ESR has NO appreciable effect on the circuit. The 1k completely swamps the so-called 1.X ohm ESR from the caps.
Agreed. That 4 ohm ESR is only 0.4% of R2. That's not a factor. Also, you do need a bipolar cap there. Yes, C25 is polarized, because it's connecting 18.5V to a ground referenced side. But the output of C25 will swing +/- with respect to ground. At this point, my best guess is cost savings. I'd change it to a film cap and call it a day. (I'm not convinced that two caps in series to make a bipolar works that well and stays completely linear.)
Agree. My Nikko Beta 20 Preamp had many examples of the back-to-back electrolytics and it seemed obvious this was to save costs since the capacitor values were common to many other caps throughout the board. I replaced with bipolar caps of high quality and transparency of the sound went up. (I eliminated 10 polarized electrolytics this way.)
I don't believe that it would be measurably worse changing those decoupling caps from a pair of polarised, to a single NP electrolytic to a film, assuming the same value - especially as is seems there is another decoupling cap on the output of the earlier stage. In fact I'd go as far as saying that changing to NP or film may even make a slight improvement. Usually the bottom end roll off limit is set by the negative feedback cap not the input caps so it shouldn't influence that aspect. I suggest they simply chose to use two polarised caps in series because it was a very common value used in the production line.
Hi, Tony... I have another thought about the two capacitors. I think there is no need for the ESR because there is a 1K resistor in series. That resistor forms a low-pass with C3... Some 3 Ohms extra won't matter... but perhaps you have a better insight.
Beautiful. I started heavily drooling when you announced more work on the sx980 was planned. I have one. It works fine ( I haven't tried to fix it yet) !!!! At 80w per channel it stands shoulder to shoulder with the few other similar top receivers of the time. Thanks for tube(ing).
Enjoying this new series. You drop a good deal of tips on how to maintain the equipment. I follow your concept on the back to back caps, it makes sense. Thanks for the look and listen.
It seems Pioneer did this two ways on this model during production. One was the way you have it there with two 2.2MFD low leakage caps configured for BP and the other is one single low leakage 1MFD bi-polar capacitor which is what is in the SX-980 i am working on now. So it seems you can actually go either way. The board number on mine is AWH-073
Appreciate this because bought one (unfortunately EBAY, seller was horrible shipper) about 18 months ago. Been good to me thus far, all new LED, adjusted BIAS (did not blow-up) new paste all SCR's. Mainly for looks, when I do use it do not turn it up too loud (needs full blown re-cap). This along with my Kenwood 9000G are my Art. Enjoyed the Relay education and have never looked for the tape and magnets, now will have to remove cover and see.
I have this very same receiver. I'm happy you have a video on it, I am looking forward to more video's from you on this fine receiver. So far mine is working great but may need to do some work on it in the near future, so your video's will be a Great Help!!!
I suggest that when you clean pots or switches with silver plated contacts do not polish the silver clean. First of all tarnish i.e silver oxide is ugly but conductive. Other contaminates lift the contacts apart causing intermittent contact. First I would decrease with alcohol then to convert the silver oxide back to pure silver do this, line a glass cup or bowl with aluminum foil and add some warm salt water. When you place the silver part in the container and it touches the foil it will almost instantly turn back to shiny silver. This works on the family silverware as well. The silver part must be totally grease or oil free. The silver is preserved and there is no rubbing. The butler can find something else to do!
Yeah .I had this model back in 1991. The start up delay circuit went west and it would not play any more. It powered my Fisher Studio ST 460 Speakers and had a great great sound.
FWIW I have a similar vintage TEAC BX-550 which I recently recapped. I note the amplifier has 2x 10uF/25V capacitors in series followed by a 1k resistor. These being found in the input of the moving coil circuitry. Yet no such arrangement is used in the moving magnet circuitry.
Tony, You can’t short the relay to ground to avoid a spark. It would destroy the amp if there was Large DC offset or if working Ok and playing loud and producing high current to the speakers. The relay is designed to create an open circuit to protect the amp from the load. Other wise you explanation of the relay and how it works was great.
That's not how it works. The speaker is what is shorted to ground. In that type of relay configuration, the common contact of the relay goes to the speaker, the normally open goes to the amplifier output and the normally closed goes to ground. This will greatly reduce the arc flash as the protect relay drops out. This is a well known method that increases the life of the contacts. The speaker is changing the connection, not the amplifier output. Some amps are not wired this way and the relay connections must be modified for this configuration.
My 980 has amp board awh-073. Instead of having the two 2.2 caps on the board it has one 1micro low leakage cap. The other slot is solder filled from the factory.
I've seen that 'series' cap designed used with other power amp at the signal inputs. Randy Slone (RIP) used that "dual cap design" a lot in his books. (The Audiophiles Project Source Book) But he uses tantalum caps. From what I've read and seen it's a common design technique. One amp design uses two 22uf tant. caps right at the audio input to the diff. pair. Not sure why they use tantalum caps. Maybe better HF transient response and lower thd than standard electro caps ?
tony I watch each of your video , it's very learning about the different amplifiers from 70,80 I try to find oscilloscope used , any equipment star my laboratory if known any person can help with donation multimeter, power supply, funtion generation the don't need.
Yes but with the two capacitors tied Together you're saying increases the resistance esr but in the circuit diagram shows a resistor in series why would you need the high ESR on the capacitor if you have the resistor in series with it? I'm not convinced party that argument!
Yeah, your right about those fake repair video's of equip that was supposed to be found outdoors, one had anamp that was supposedly in a drainage ditch for a couple of years yet when they cleaned it off, all the metal traces , solder joints ,capacitor plastic covers, enameled chokes, they all looked brand new clean, i gotta call B.S on that!
Maybe they were put in there as redundancy, just in case one shorted? Your frequency response would change some, but not much. Seems this explanation would be better suited for coupling between stages though.
The problem I have with the ESR idea is R2, a 1k resistor in series with the dual caps. With a 1K resistor in series, 1.8ohms or 3.8ohms would be grossly insignificant.
Exactly. And another 21K in series. I Also think the ESR is not a design idea. Also, ESR is not a stable parameter of a capacitor. It changes with capacitor ageing. Most likely the film capcitor was more expensive or too large to fit in that place.
I’ve been in the market for an SX-980. How do you think it compares to the 950 in terms of restoration work and build quality? I’ve heard the output transistors on the 980 are much harder to source and replace than the 950, is this true?
I always been stumped by the two electrolytic caps in series thing. With a real AC signal that means that one of the caps at any time has half of the signal in reverse polarity while the other has it in it's correct polarity. Given that the signal is divided equally between them. When the signal changes polarity this reverses, and the other cap now has a reverse signal on it. Can that be good from a sonic perspective? I know many speaker crossovers use (or older ones did use) this configuration.
It's a very interesting take on this matter, however conclusions are simply wrong, I'm afraid. Two caps in series - anode to anode or cathode to cathode is precisely what you'll find inside any bipolar electrolytic cap. Remember that midpoint is not connected to ground.
@@paulb4661 Well of course the midpoint isn't connected to ground. They wouldn't be in series then. If my conclusion is wrong, then what is the correct conclusion? Isn't the AC voltage divided equally between the to caps or what? And if it is, then how can it then not be in wrong polarity on any of them?
@@geirendreAfter Cornell Dubilier electrolytic caps application guide: If two, same-value, aluminum electrolytic capacitors are connected in series, back-to-back with the positive terminals or the negative terminals connected, the resulting single capacitor is a non-polar capacitor with half the capacitance. The two capacitors rectify the applied voltage and act as if they had been bypassed by diodes. When voltage is applied, the correct-polarity capacitor gets the full voltage. In non-polar aluminum electrolytic capacitors and motor-start aluminum electrolytic capacitors a second anode foil substitutes for the cathode foil to achieve a non-polar capacitor in a single case. -While it may appear that the capacitance is between the two foils, actually the capacitance is between the anode foil and the electrolyte. The positive plate is the anode foil; the dielectric is the insulating aluminum oxide on the anode foil; the true negative plate is the conductive, liquid electrolyte, and the cathode foil merely connects to the electrolyte. The way I see it is, that the first cap is not reverse biased because the midpoint isn't grounded while the second cap blocks DC, hope that helps.
These two capacitors are at the input of the power amp, right? Remember, this amp has a split between pre amp and power amp (see ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Yn6KngRwhEQ.html). So if you feed an external signal into the power amp, it could have a positive or negative dc offset. With this bipolar configuration it is prepared for both cases.
I agree that it's for protection, especially since there's a 1k resistor in series with the caps. Putting them in series also doubles the voltage rating, so it's two-way protection from failures in the power amp or failures in the preamp. But why didn't they use a film capacitor? Sometimes they decide to use parts they commonly stock vs. a special part they'd have to order.
I'm afraid I would blow the whole receiver off the bench :)=) Of course, one of my friends cleans his car out with a leaf blower. Just open both doors and blow the leaf blower in one side and the trash blows out the other ;)
@@xraytonyb I was told that one should never blow dust but vacuum it up because it could contain many toxic particles. At minimum, it should be done outside while wearing a mask. Could high pressure shop air damage any component in a receiver? cheers Mark
i have this same receiver, pioneer SX-980. i understand you do not repair by request. about how much would i be expected to pay to have my receiver given the once over. cleaned, recapped, tested for any failures. THANK YOU.
I was wondering if you were open to doing an simple experiment I have a Yamaha rx-a1080 receiver which has an ESS 9006 sabre dac which I want to change to the more current 9026 DAC and replace also the adc chips too to make improvement to the dynamic range Yamaha went with 10 year old dac instead putting in the most current one The unit is totally functional and taken care of. I was greatly disappointed with Yamaha.
Interesting about the caps in series. I am recapping a Sansui AU717, it has a switch to select between pre-in/main. On that pc is 2 electrolytic's in series to decouple the input. Next to those caps is a open spot for 1 cap. So they had the option of using a film there. Debating what to use there, it seems most restorers use the film option. Interesting Sansui did have the option, way back in '78.
Why don't you do both one and one Channel one on the other and compare what you think is better sounding And if any test show any changes like in distortion harmonic distortion
@@johnsweda2999 Good idea. Thing is, I don't have any way to measure distortion. Also, highly doubt I will ever need to use just the main amp input. The switch is 3 position, with 1 of those by- passing the decoupling.
@@targetedindividualsresearch Glad you quit your nasty stinking disgusting habit. My comment was meant for gear that was subjected to long term cancer stick exposure. The crap that was sticky from the nicotine etc. The shit that literally has to be washed down from the stench alone. When I read that someone has lung cancer from their life long habit and is crying the blues because of their situation I just smile. No one put the 1st one in your mouth and not a damn person gives a rats ass about what happened because of their bad life choices. I have paid more for used gear that didn't smell like shit. Just my 2 cents.
Actually! What is the difference between polarised and non polarised capacitors? I don't think that I have ever seen or heard a talk about the difference between the two! To my understanding, a polarised capacitor will only charge via DC if installed correctly but I don't know if this is the case with non polar capacitors? I somehow thought that AC can pass both ways but now I'm not so sure... I generally see non polarised capacitors being used in speaker crossovers but I have also seen polarised capacitors also being used as a high pass on tweeters in cheap home speakers and especially with car tweeters... Either there's some benefits to using one or the other or there's something else that I'm not aware of? I would like to also say thanks for testing some old capacitors and comparing to new.... There's something soothing about watching this take place even though there's no point to it LoL.. I would like to ask you if you consider yourself as a repairer or a restorer? The reason behind this question is that for some time, I was watching videos by a lot of different people who work on electronic equipment and it seemed that everyone is doing the same thing! As a consumer, when something goes wrong with your equipment, the first thing that you might think is that you need to find a repair man.... But after watching a lot of people work, I feel that there are really two different types of people working in this trade! I feel that a repairman is something that I don't want to touch my equipment! I don't want just the failed components to be replaced without finding what caused them to fail in the first place! Yet I probably wouldn't have gone looking for someone to restore my equipment simply because it just sounds expensive even though, especially if you value your equipment, it's actually the cheaper option... I have had equipment so called repaired before only for it to stop working at a later date and because of the same problem! People who restore in my opinion are far and few in-between... I watched a video by Uncle Doug where a customer sent in a tube amp for repair and the accompanying letter from the customer clearly stated that he wanted Doug to work his magic and cost was no option! This customer clearly understood the value of his amp, knew the quality of workmanship and knew that for the money spent, it should not fail again for at least another 40 or 50 years of service! Of course there are times when you just have to get something working just enough to transfer media or something like that before it gets thrown out because it was probably junk equipment to begin with but I see a lot of people work on beautiful vintage equipment and they won't go right through and check everything and then they do something stupid like replace perfectly good speaker terminals that an engineer with a far better understanding of what that amplifier needed with huge gold plated brass terminals when it makes no difference whatever to the sound even though that's what they thought they were actually achieving.... Look at me! Now I'm ranting! Sorry! So basically.... Restore, don't just repair!
A polarized capacitor is designed to handle 0V to it's working voltage - but only in the one polarity. If the capacitor will see the polarity reverse (as in this case), you should be using a non-polarity cap.
Yes, there's a lot of fake "barn find" videos of people making a brand new car or something to look 100 years old and making a video of how they fixed it for $1.29. Now, in THIS very video how do we know YOU did not clip that resistor lead? Hee hee hee ha ha.
