Pioneer SX-780 Service! - Easy!! [45 WPC!]

In this video, we go through the servicing procedure on this beautiful vintage Pioneer SX-780 receiver!
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Link to Service Manual:
www.audioservicemanuals.com/p...
Contents of this video:
00:00:00 Intro
00:00:42 Tools Required
00:01:17 Visual Inspection
00:02:36 Switch Cleaning
00:04:41 DC Offset Adjustment
00:10:22 Wattage Needle Adjustment
00:13:32 Signal Testing
00:16:46 Wrap-Up
#vintageaudio #vintagerecevier #vintagepioneer #pioneersx780

[@patriciawilson9666]

Awesome video on the 780.I've owned mine since high school 1979.

[@TinkeringWithT]

Thanks for the kind words! That’s awesome! The 780 is a beast. Never sell it!!

[@patriciawilson9666]

@@TinkeringWithT Yep,she's staying with me for life.

[@Truth-Machine5000]

Outstanding video. Thanks for taking the time to post this.

[@TinkeringWithT]

Thank you for the kind words! Glad you enjoyed it! Thanks for watching!

[@dbg4651]

Good job. Very nice video.

[@TinkeringWithT]

Thank you!! and thanks for watching!

[@Gabrielishere]

I keep re-watching this just to see "we're removing those screws... ☺" LOL

[@TinkeringWithT]

😂😂 that’s right!! We gotta get in there for some service!! Thanks for watching!!

[@PrecisionClays]

When you were doing the DC offset adjustment the instructions show that the meter should be set to DC. It really looks like your meter is set to AC. The meter drive circuit adjustment is AC.

[@TinkeringWithT]

You’re 100% right. I realized my meter was set to AC after I finished filming. Off camera I rechecked set at DC.. forgot to edit that! Thanks for watching and pointing that out!!

[@doYYY-gq1ox]

Nice video. Do you do recap for the sx-780?

[@suasponte6230]

Very good. A second camera showing up close would have been great.

[@TinkeringWithT]

Thanks for watching! I’ll definitely add a second camera from now on!!

[@dennisstreet676]

I have a pioneer sx780.

[@TinkeringWithT]

They are great receivers! It’s one of my all time favorites!

[@jmad627]

I have one of these models and have just noticed that the left VU meter needle doesn’t move. I’m not noticing any sounds difference. Just watching your video to see what you’re doing and if it may help figure out what happened to my receiver.

[@joshualightner6548]

Have you tried replacing the Darlington packs with STK-0050+ models? Much more reliable 😉

[@TinkeringWithT]

It's on my list of things to do! I will definitely be replacing with those modules in the near future! Thanks for the tip!!

[@baileyscot]

I have my dad’s sx-780 that’s been sitting in it’s original box since being replaced on the rack in our home around 1990. Would you recommend opening the case to inspect before attempting to fire it up, and if so, what would you be looking for? Capacitors bulging, resistor burns, just dust everywhere? Is it worth just turning it on to see where it sits, or is that super risky?

[@TinkeringWithT]

Awesome!! Definitely wouldn’t hurt to open it up, and give a visual inspection on the components. Check for leaking/bulging caps/burnt resistors etc. if everything looks ok, I’d plug it in to see if it works! Let me know how it goes!

[@baileyscot]

Everything looked OK so I fired it up. Initially Left channel wasn't coming through but some fiddling with the switches and it's there. I need to get some deoxit in the switches and probably make those adjustments to the trim pots for the DC and for the VUs. I'll be following along with your video. After that it's time to look into the RT-707 that was with it in the barn...

[@StephenAtt797]

Great Video, I got a 780 about a month ago. After testing found that the left channel would go silent (meter would stay fixed), or more often produce some crackle/static. Powering on and off generally stopped that and would rarely or ever repeat over 2-3 hours of play. Had tried some CRC-26 from the outside, no help. Finally last week got some Deoxit and again from the outside, hit all the switches and now 3 days running for hours - no static. My problem now is the balance POT. Seems to be frozen, Cannot turn the knob at all and when I took knob off I see that one of the half prongs is gone. Should I assume the POT is now useless and should be replaced (I can source a replacement), how hard is that to do? Do I need to remove the face plate, or can it be done via access thru the rear? I've never worked on AV equipment, done some PC work and model trains. Tools are limited to a Multimeter and soldering irons. Alternately, is there any way to adjust the Balance POT (to EVEN) via inside access? I have no need to really alter balance based on the listening area and my streaming device has it's own EQ adjustments.

[@TinkeringWithT]

Sorry for the late response! Thank you for the kind words! Congrats on getting a 780! It's one of my favorite receivers! Glad to hear you got the the dirty switches resolved! If any of those switches get dirty, they can cause all sorts of weird static/channel going out problems. Bummer about the balance knob. If it's frozen, I'd start by shooting som contact cleaner/lube inside of it and gently attempting to turn it to see if you can break it free! Chances are, it'll still work fine! Give that a try first. If that doesn't fix it, I can look into how to replace the balance knob. The way you know it's centered is when you turn the balance knob, you'll feel a little detent while turning it to let you know that it's centered. Let me know if you get the knob freed up!

[@StephenAtt797]

@@TinkeringWithT thanks... I have tried getting Deoxit in via the front knob a few times, haven't noticed any difference. I've been reluctant to remove the case (though it looks pretty simple), I wonder if getting Deoxit in the POT from the inside would work better. Other than that issue, it's been playing great since I got rid of static issue.

[@TinkeringWithT]

Yeah, I think the best way to clean it would be to get inside and have better access to the internals of the pot! Glad to hear it’s playing nice! The 780 is an awesome receiver.

[@shawnbledsoe6325]

so this pioneer has darlington power pack stk-0050 do you know where a person can still by these

[@TinkeringWithT]

Yes it does! I have read that there are lots of knock-offs for sale. Some people have had great luck with them, and some people say they stopped working after a few months. I read a forum awhile ago on building your own modules out of modern transistors. If I can find it I’ll attach the link!

[@BTL3.0]

What does it mean if the dc offset won't stabilize? It bounces around quite a bit, it doesn't stay put like in the video. Does this mean the Darlington power pack is going bad? Also, are both vu needle supposed to swings the same? My left needle feels lazy or swing lower than the right. I've done all the adjustments exactly as shown in the video. Power pack appears to be original but uncertain.

[@TinkeringWithT]

Usually if the DC offset wont stabilize, it could be caused by a leaky capacitor and/or transistor that’s allowing some DC to pass. If the unit is all original, I’m sure it could use a re-cap at the very least. Luckily the 780’s aren’t too bad to recap. Does clear sound with full bass and treble come out of both speakers? If so, the Darlington’s are probably ok. When those start to go, one channel with either start to sound flat and distorted, or go out completely. The needle situation could be tied to the Darlington issue, if one channel is weaker. Does the right channel seem like it has better sound than the left?

[@BTL3.0]

@@TinkeringWithT ok thank you. Can you look at the video i made the measurements for the dc offsets? Showing the reading. Pioneer Sx-780 DC offset reading, normal?? kzbin.info/www/bejne/a37RhK2pZauDkNk Let me know your thoughts. During inspection it appears that everything is original. Im not sure if the original darlington pack have number from 1-9 printed above the pins. But mine does. Each pin is numbered in white.

[@ivy488]

When you are adjusting the Watt meters, what is your multi-meter connected to? Service manual says to connect the voltmeter to the A speaker terminals. How do you do that?

[@TinkeringWithT]

You attach the leads of the multimeter to the place where you’d normally connect your speaker! The Black and red terminals on the back. Attach the meter on the Channel A or Speaker A side. Black is “-“ and red is positive “+”. I’d attach a picture but I don’t think I can in the comments! I think In one of my other pioneer service videos I included a picture. Let me know if you have any more questions!

[@ivy488]

@@TinkeringWithT Ah, OK. Thanks. So, it doesn't matter if you attach to the right or left speaker?

[@TinkeringWithT]

No problem! I don’t think so as long as it’s on the speaker A side!

[@TinkeringWithT]

Just make sure your balance knob is in the right spot!

[@joshualightner6548]

Glad I read the comments, as I was about to ask the same question. I'm about to do the identical project here in a little while. To answer the question on which speaker, no it wouldn't matter as the Voltage will read the same since the adjustments on VR6(Pin 6) and VR5(Pin 9) have identical ratings at mV. Thank you for this video 🙂

[@julioguillerman9160]

Hello again ...!!! attentive to your instructions I dared to try to clean the variable commands of the equipment, after applying contact cleaner and drying it with a little pressurized air, it improved but after a while it failed again, it happens that some of them produce a noise like frying and , the channel that fails , now it is heard very softly , is it possible that the dirt produces this effect ? I ask, is there another cleaning technique, let's say deeper, or do I directly change the two Darlingtons? I thank you for the courtesy you dedicate to my query , which is in fact the last , I do not want to err on the side of boredom . I clearly realize that you are not a fortune teller hahahaha...!!!

[@TinkeringWithT]

Definitely! Dirt in the switches could cause a channel to drop out. Does the channel come back when you mess around with the switches? If so, you could isolate which switch is causing the signal drop. If it isn't a dirty switch, I'd suppose the power pack for that channel has failed or is failing. Keep me posted on what you find out!! I wish I was a fortune teller!! haha.

[@julioguillerman9160]

Very good video ... congratulations. I take this opportunity to ask you since I have one just like it. It turns out that one channel works fine but the other works very weak and distorts. I live in Argentina and I would appreciate it if you could advise me on what I should change. Thank you very much for your attention !!!

[@TinkeringWithT]

Hello! Thank you for the kind words! If I had to guess, first make sure all the switches are nice and clean! A dirty switch can cause distortion on a channel. If that doesn't fix it, I'd say one of the power packs is starting to fail. The 780 using a Darlington Power Pack for each channel, and they go bad after 40 years. They are fairly easy to replace if you have a soldering iron! And they are pretty cheap as well! The part number for the power packs is STK-0050. Keep me posted! and let me know if you have any other questions!

[@ismaelsalas9819]

Where are you located

[@roninnovastar1321]

Once again, your output record volume is to low. I even transferred the signal to jbl bluethooth pod was able to hear a little bit better, but still very low volume still can barley hear, no problems with my hearing.

[@TinkeringWithT]

Thanks for letting me know again! This was my first video on KZbin so I hadn’t fully figured out all the volume adjustments.. hopefully the new videos are a little louder! Thanks for watching!

[@roninnovastar1321]

Thanks for reply and showing concern !!

[@TinkeringWithT]

Of course! Thanks for letting me know!!

[@ReginaldDj1]

That's the wrong contact cleaner

[@TinkeringWithT]

Yeah, It's all I had at the time unfortunately.. I got some De-oxit and went back over the switches a couple weeks later. Sounds great!! Thanks for watching!

[@ReginaldDj1]

@@TinkeringWithT yeah no problem because I use to use that and I always had to go back and redo the buttons and switches until I found out I was using the wrong contact cleaner 😂 I had never heard of deoxit 😂 but I do now and I use it religiously. But I do have a question I have the top of the line vintage Fisher stereo receiver the 1080 and I've been trying to adjust the DC offset and bias I followed the manual hooked everything up but when it comes to adjusting I turned them a little bit at a time but I get no movement on my volt meter and it's in the right settings Mv even though the dial is turning this is blowing me away because I also have a Pioneer 1080 and I set the DC offset and bias on that with no problem so I wonder what's going on with this Fisher.

[@TinkeringWithT]

Same here! I learned my lesson as well. De-oxit is the best! I like to use D-5 on switches. Really seems to get the job done! Oh nice! That is a beast! Hmm, I'm not really familiar with those units so I'd have to pull up the service manual. Sometimes the receivers have to be in a certain condition to check DC offset, like no volume, no input, no speaker load etc. Does the manual talk about that at all? If that's all good, maybe double check you have your multimeter in the right area, there have been countless times where I have been checking the wrong areas! ha! Does the unit work ok? Does it make good sound? I'll take a look into the service manual.

[@ReginaldDj1]

@@TinkeringWithT yeah the Fisher plays great but I'm trying to be a perfectionist and get it down to total ZERO the Right channel is at 8.1 and the left channel is at 10.1 and I appreciate you looking at the manual.

[@TinkeringWithT]

@@ReginaldDj1 No problem! I'll try to take a look at it today. Has there ever been any work done on the unit? Or is it all orignal? It couple be possible that there are some leaky capacitors that are allowing DC to pass to the speaker terminals. Also, is the DC offset adjusted by turning a VR? I've read the the VR's used in most of the old receivers are no good, and fail over time causing you not to be able to get a good DC offset reading. It's happened to me!