I love this. And I love the way you speak when you teach. It's like you are talking to a good friend when you explain things. No cursing, which I like! One thing I noticed, you speak about a 5.1 ohm resistor, when in fact, it's a 5.1K resistor. The manual says that, but just to be clear.
Very helpful info on the bias adjustment and protection board. My SX-950 relay doesn't even kick in regardless of how long I wait after power on although the panel lights come on just fine. Thank you for the tip, most appreciated!
Wow, this is so helpful, thank you! I just bought an SX-850 and the only problem thus far has been some pots that needed a little cleaning. It sounds wonderful! I will eventually recap it and replace the speaker protection relay. I found a couple of people on eBay who sell SX-850 repair kits including the relay and the large filter caps which saves me the trouble of figuring out what parts to buy.
Thanks for this video! This will come in handy when I finish my first HIFI restoration on a Pioneer SX-950 later this month. I cannot wait to hear how it sounds.
Thanks so much for this video!! I just replaced all the caps and the suspect transistor and installed the diode as you suggested. I also biased the output and it appears to be running great.
Thanks so much watch your video I able to adjust my sx-980 both DC offset and Idle current. It was big different. Now i need to figure out how to adjust Meter amplifier.
Thank you for the excellent video. I have a SX 980 with speaker protection relay problems. Would the work you did on the 850 in this video be applicable to the 980 as well or is the 980 constructed differently?
Nice instructions. I always wondered what no load meant. I had a problem with the relay turning off the speakers after 10 minutes of use. Then after a few minutes it would turn them back on. It would do this for a while and then just stay off. I checked the voltages of the transistors on the protection board with speakers off, had no choice. Q1 and Q2 voltages were way off from the schematic, so I replaced them. Now when the unit turns on the relay clicks after 3 seconds and doesn't click till I turn the power off. Seems to work. I will have to do that diode thing.
Regarding the protection mod, you can bridge 9 and 10 or 9 and 11 with the 1N4004 diode. Cathode end connected to 10 or 11. Looking at the back of the PCB, the tracing shows 10 and 11 are connected.
The 5.1K resistors are interesting. I have done other Pioneers and the manual was nothing like that. Is it that way to keep the input to the amp board at 0, cause one may not know what coming out of the preamp. Something to think about. Great video.
I'm currently working on a SX-950 where I'm getting odd voltage measurements at the inputs and outputs off the power supply and the protection board. For example the input from the transformer and output pins of the power supply, protection board, eq board, tone, flat amp and power amp boards shows voltage being way off compared to factory specs in the service manual.The condition presently is the unit powers up, no indicator lights, the dial light comes on but not hearing the click from the speaker relay and no sound. Have gone through those boards and replaced capacitors and some transistors as needed, checked and rechecked the diodes, caps, transistors and resistors and all are as they should and installed correctly. At this point I'm suspecting a bad transformer, is this a valid assumption? Your thoughts appreciated, thank you!
Mark, Great video, as usual. I have learned a bunch from you and I'm going to start working on some of my vintage Japanese and American audio stuff, soon. I've worked on loads of tube radios and even a couple of TVs, but solid state stuff has so far seemed a little daunting to me. Can you tell me the name of the band and the album that you were playing? I know you said it, but I want to get the names correct. It's awesome stuff and I'd like to know if it is available yet to purchase. Michael
Thank you for your informative videos. You helped me with my Marantz 2215. now I need help setting offset and bias on my dad's Pioneer SX-1500TD. The manual doesn't say where to adjust or what level each should be on the vmm. Do you know? Make a video servicing this receiver? Any help would be great!
Sadly I don't own one to make a video of it. Off-set it easy, adjust until you have 0v DC on speaker terminals. Bias maybe tougher and you would need a service manual or do some searching for correct values
I would say job one of the protection circuit is to protect the speakers from the amp (in the event of a large DC offset) and not the other way around. Yes, they do current (ASO) sensing but many times the amp will blow anyway in the event of a short. Not so often on this series of Pioneer though. Been repairing professionally for 35+ years. Personally, I prefer to troubleshoot and repair problems first, re-cap second. By the way - Q5 on the regulated power supply board is pretty notorious on these. It's a series pass transistor for the relay B+. No sound on an SX-850, this is the first thing I check - no B+ on either relay coil connection.
Mark, you look a little young for 35 years on the job! Seriously though, I imagine you and I would be similar age and experience. I also started in the early 80s and have fiddled with / repaired / sold just about every audio device ever made - even at this moment I have to be careful where I tread for fear of standing on a dangerously shaped Hi Fi related component. Regards from London.
Blueglow Electronics That's amazing, I am similar with age, but without any entrepreneurial bent. I had a friend at school who showed me some kits he had made with LEDs and 555s etc. and I was hooked. Within a year I had built my own computer (1978) and soon after discovered I loved Hi Fi.
Billy Amundson they make a tool for unwrapping the wire. I seen it on an earlier video, someone else put up. I've watch so many today. Only thing for sure it was in a video on a pioneer
Mark, have you ever worked on any reel-to-reel tape decks? I have an old Teac A-4010S I've been trying to fix for awhile. The problem I haven't been able to fix is with the relays. Only one channel engages into record mode and the other channel does not engage because the relay never energizes. I'm not sure what component(s) are failing and preventing power to the relay coils. I've already replaced all the main electrolytic capacitors in the unit. I don'w know about the transistors causing this. They're all old PNP germanium transistors.
I have worked on many. Sounds like a driver transistor acting up. Probably need to dig up a schematic and chase that down. BTW I officially don't work on R2R units any more, way too complex for what people are willing to pay...
I was suspecting it's a transistor next. When I originally got the unit, the one channel engaged for a fraction of a second and then cut out. But I don't know which exact one is causing issues. I do have other R2R decks to use for parts, so I could probably swap one out And I have a Peak Atlas semiconductor tester.
Hello! I have a question, It may be obvious to most, but for me as an amateur I want to make sure... Is the 1-15 clear plastic side for the left speaker and the 16-25 for the right speaker? I have cracking and poping in my LEFT speaker and I want to (hopefully) fix it by changing out the correct transistor. I'm thinking Q7, Q5, or Q9? Please help. Thanks!
I did this process on my SX950 and you were right, It wasn't easy but being careful, and with the proper tools I did it! and it is now AMAZING!!..thanks to you! Thanks again!
An excellent video tutorial. Thanks! However, I do not understand how the setting can be the same for the SX-850 as it is for the SX-950. The procedure is the same but shouldn't the setting values be different since the SX-950 is rated at 85 watts per channel into 8 ohms and the SX-850 is rated at 65 watts per channel into 8 ohms. Why is the 20mV value setting for VR3 and VR4 the same for both and why 20 ?
I've a SX-950 that powers up, dial lights come on, the bias was adjusted correctly but the relay doesn't click on. I replaced the Q7 with the KSC2690AYS and did the mod with the 1N4007 between pins 9 and 11 on the protection board but it still doesn't click on and there's no sound. Any ideas on what could be happening? Thank you for your reply! Gabriel
@@newgilligan3694 I finally got it to function properly but not without the help from Audiokarma on the Pioneer forum. I'll have to dig through my notes from two years ago to see if I made a notation what may have been the issue but I believe it might be I didn't set the idle voltage correctly, not sure.
Replaced all caps in PS. Was going through bias procedure, Can't get The VR4 adj. below 300 mv. all other adjustments are spot on. Should I be worried?
300mV is too much. You should check the pre-amp section. Any DC generated in the pre-amp will be amplified by the power amp if the amp is a DC coupled one.
I would agree. However, I've tried to not make it a practice as I work on a lot of tube gear as well and grabbing a pot with a few hundred volts cruising through it can be enlightening...
