Pioneer SX 750 Repair & Restore Part 2

[@mikepxg6406]

Fantastic Job. Nice to look back at these older videos.👍

[@aantonis]

I found your channel a few weeks ago and I m already hooked. Well prepared videos, your voice and speed are not boring at all, which is IMHO the plague of these kind of videos. Although I don't have an FM modulator to follow the troubleshooting, your logic and walkthrough is invaluable to tinkerers like myself. Thank you and happy new year!

[@bladzmetube5589]

Hi , Thank you for sharing vintage equipement with us , Becaus of you and a few , just got me self a Realistics sta-95 just out of the crate condition , inside and outside , , i give my amp to who ever someone finds a scratch on the wood , the wood is as nice as the day it was built ,the inside is as new as the outside ,No sign of wear , I'm completly stunned over how lucky i am to have this '' Beautiful amp , i'm looking at it in the dark all lit up ,, Stunned angain !! , pinching myself , After whatching you and VintaManiacs like us lol . If it wouldn't be for you , Never i would of landed on the brand new Realistics sta-95 , The inside is brand new , , no dust ,nothing , Thank you for sharing your passion and your Vintage wisdom with us :) o7..

[@c5back9]

I had a beautiful SX-780 which I purchased new back in the day that was my pride and joy for a long time. Many, many hours of gorgeous listening pleasure was enjoyed through it, but sadly in a moment of thoughtlessness I allowed someone to convince me to let it go. It was in flawless condition with hardly a mark anywhere on the face or chassis and it operated perfectly. Like millions of other owners, I let it go in favor of newer technology which as we all understand today, never came near in quality. Have been through about 4 or 5 far more costly modern systems since that have not delivered anything near the sound quality of my late 1970s Pioneer system. And I don’t want to think about the album collection I let get away either. I hope whoever ended up with it all appreciates it as much as I did.

[@timcorner2821]

I know what you mean, I have a mint SX-780, which I have just done a full service ( first one since 1978), as I purchased from man who bought it new. It too was in mint shape. With the new STK pack Modules and recap, she is just humming. I will never part with it.

[@MrPageplayer]

Found this channel wondering how to fix an old receiver and was hooked on this series from the start.. Will sub and watch more. I think i found a new hobby!

[@braddokken9191]

I love how you approach your diagnostics. I'm learning about circuits, but I'm learning even more about problem solving. Thanks for the videos!

[@ka0kuj599]

Nice work. That will be enjoyed for years to come. A long time ago, (1978?) and nearby Pioneer dealer had the top of the line unit SX-1250?? with watt meters. The wood case was replaced with clear plexiglass. It was so cool.

[@kennethiman2691]

I am a bit OCD. That front case misalignment would drive me to distraction. Wonderful job on the restoration.

[@MrElectrowhiz]

Thank you for this video. Your final results of the FM circuit is great. Dippin' Dots main facility is just a few blocks from where I live in Paducah Kentucky, and it was invented in a small town of about 300 people in Grand Chain, Illinois.

[@paulcyr64]

I have a SX-750 that I repaired and restored about a year ago. I just love that receiver hooked up to the Pioneer HPM-100 speakers. 😎

[@marsattacks7071]

Beautiful job ! The nicest way to recycle good products (since we no longer have the option of buying good well built units that can be repaired, improved, etc). Thanks !

[@nunyabidness9301]

Just want to say excellent video, and thanks. Acquired an SX1250 that I'm getting ready to re-cap. Receiver is in good shape but I was going to check all the tuning. The old Pioneer manual was throwing me on the RF output levels. I was pretty sure it was -100db, but could not find anything, anywhere, to verify it. Big help!

[@davidsanderson1788]

Great video. I didn't cover FM tuner design in such detail before as an eng. under graduate decades ago, so I learnt much from the videos. I recently got out my SX 750 that I bought new in the 70s. It's not been used since about 1995. Unfortunately the power switch selector spindle has broken off so I need to find a complete new switch assembly. The switch contacts are good as I remember cleaning them 20 years ago to solve the arcing problem that plagues these receivers. The only other internal issue is blown bulbs. 8v ones used by the factory are virtually unobtainable so rather than replace with LEDs I use 12v 80mA filaments on the indicators. On the dial illumination 12v 5w wedge type bulbs work fine, also known as T10 or 501 auto bulbs in Europe. My unit is a UK version and there are subtle differences compared to the US versions. Mainly around the mains power supply being 240v 2 line in the UK. Also, I wonder if the 10.7 MHz filters on the FM tuner are different bandwidths to deal with differences in FM station separation in the UK compared to the US? In your Part 1 video you talked about some wire wound posts being soldered too suggesting repair work having being done at some point. Mine has some soldered ones too but I know it has not been touched since new so they must have come from the factory like this. I have also not found any suspect looking caps. so have chosen not to run through replacing them as a matter of course. Maybe as my Sx 750 has been stored in cool conditions for half its life the caps are in better condition than units in warmer parts of the world like the US. My cabinet was tatty too after 40years with the walnut finish peeling off. The original SX covers on the lower range models have an artificial walnut finish whereas the higher end receivers use a real wood veneer. I thought about making a new solid wood cover as well. In the UK we have a product called Fablon sticky back plastic which is easy to apply and trim with a sharp knife. The 'Walnut Deep FAB10886' colour is a good match to the factory finish so much so that I did not need to recover the whole of the unit, just the peeling side panels. It's very quick too compared to making a solid wood copy.

[@xraytonyb]

David, Great tips! I also restored a multi-voltage version of the SX-750. It had a rotary voltage select switch on the back panel to select 120/240 Volts. Other than the transformer and a few things in the power input, the rest of the receiver was the same. I didn't notice the filters in that version, as they were working properly. I could see how they would use a different bandwidth filter for the UK, but I don't know for sure. That's interesting to know that you had some wire wrap posts soldered as well. The SX-750 is a great receiver. I hope you get yours up and running too!

[@davidsanderson1788]

Tony, thanks. Yes I think the SX 750 is good too. Enough power for most home systems. I have not heard the higher end SX receivers like the SX1250 or SX1980 so don't know if they are significantly better in terms of sound quality. For sure the SX1980 would blow out the windows in my house on power! They seem to have hit very very high prices too. Good if one can get hold of one cut price that needs fixing and has the knowledge and equipment to do so.

[@jonka1]

You talk about how difficult it is to check if the local oscillator is running. If you make a simple coil pickup of a few turns on the end of a scope probe you can approach the oscillator coil and detect a signal without affecting the operation even slightly. I have several for different frequencies and can even couple them to a counter to check if the oscillator is on frequency. This simple tool takes all the mystery out of these circuits and will save lots of time agonizing over the local oscillator setup.

[@g.fortin3228]

I like that model and nice job , great explanation and the wood looks nice too.

[@poormanselectronicsbench2021]

@ 5:10 One could possibly, wrap each case with some kapton tape ( the sciencedirect site says kapton tape is actually a thermally conductive item) to insulate them electrically, then create a mechanical thermal coupling clamp by using 2 pieces of aluminum bar stock about 3/8" thick, clamping them together, and drilling vertical holes in the seam correspondingly just larger than the transistor case bodies, then drilling possibly a 4-40 sized hardware hole to use to clamp them around both transistor cases. It's a bit of fab work, but probably doable as long as one could get the right drill bits for the case sizes.

[@brig.4398]

A good video, learned a lot. A bit long but by going slowly I was able to follow along with everything you did. That Duo Transistor must be a proprietary part.

[@MickeyMishra]

I'm really sad for radio receivers. It's not that they're Antiquated or they're bad for any reason it's just that almost everything on the radio is garbage today. and you're lucky if you just have one station that's at least decent. not piled full of digital stuff they're pushing on their side band or all the other Malarkey they're doing these days with radio.

[@martinexner6038]

Thank you you re a very good teacher

[@johnbeckham1483]

AM tuner was good while the FM was totally mute on the Pioneer SX-750? Changing the selectivity of the FM bands with filters! When in doubt play in the Caution League indeed!

[@keithbarker6311]

Good video. I would like to some of the rework and disassembly as I always learn by watching others. Thought a bit about the SG settings suggested in the service manual, and they might be referring to dBf units which is relative to a femtowatt. I think 100 dBf corresponds to a -20 dBm output into a 300 ohm load (if I did the calcs right). That, I think, is where they are setting the signal strength meter. Just a thought.

[@PhutureprimitiveRulz]

Keep up the great work!!

[@jonka1]

Like you I live without decent radio signals including FM. For about £80 I have my own low power stereo fm transmitter which takes its signal from a satellite receiver and give a perfect reference signal for the receivers I repair. I have also set up a similar AM transmitter so that I can listen to my many vintage valve radios. This fm setup may be something you could provide for yourself.

[@joeboy7433]

Thanks for a great video and explanation. Truly master of your craft

[@erdemkuter8198]

good fm repair .. thanks

[@scottgreen6426]

Scott Green, I also have a SX750 in operative condition, put main filter caps in a number of years ago, now I’ve got a common hum across all inputs, I am interested in recapping this receiver, and I’m interested in your poly caps that you’ve chosen in place of the tantilum caps, I’m also interested to know whether or not you have ever sold capacitor kits that would do a recapping job on The most prominent points on the receiver and amplifier, for this model SX750

[@catman58]

That was a lot of work, I learned a lot thanks

[@walkingrobin9965]

Great video

[@rickraney3939]

T, I love you man! Super great video, there's a but coming...... PLEASE Use a thin pointer...NOT your hand! And PS, that is exactly what is happening to my SX828's tuner. So, now I have some baseline to go by. THANKS!

[@slimjim119]

U And YOUR Family Have A Happy New Year

[@jeffhayes4845]

Hey, can you share your process/method for cleaning the face plate? Thanks for the video's. Very interesting.

[@stephenfarrell6794]

Really enjoyed the videos! Have you ever worked on a SX-9000? I still have mine that I bought in 1971 and am trying a few simple things. I ordered the DeOxit as recommended by someone and waiting on it getting here. After watching both parts I now know to be careful where I am spraying it.

[@jakep8484]

What about using sa992 transistors in plastic case then using heatsink compound

[@lelandclayton5462]

Thanks for the video. A friend of mine has the same system however his system has a dead channel (probably the relay to the protection circuit is dirty). He keeps complaining about it and I kept telling him to bring it to me and I can get it working again but he never does lol. Cherry and the flat black on the top works well together and the brushed aluminum makes it pop. Looks better then most high end systems. Since you're a carpenter as well I have a question. I want to build a custom case for a power supply and I think it would be neat to use a old layout (kinda like your Eico Signal tracer sitting on your bench). The rear, top, bottom and sides as a wooden box probably plywood and a aluminum face plate. The question is should I use box joints or just go the easy route and use butt joints.

[@jimmycake7143]

Isnt there an adjustment for the stereo indicating or seperation or MPX?

[@nordland2235]

I have a Pioneer SX-850 it is cosmetically mint.....and plays ...but has issue that needs repaired.

[@zarmindrow5831]

you restored the shit outta that 750 yo

[@nordland2235]

All caps have a shelf life.....right ?

[@call5sam]

Is your Sig Gen calibrated? If so, how did you calibrate it? That would be great to see.

[@chuckesley8071]

What was the replacement number for the transistors you replaced?

[@johnbeckham1483]

Are those NPN or PNP transistors? What is the theory here?

[@kenelsbernd276]

Nice 👍!

[@ThejasonJaw5442]

Related to a dual transistor pack what's the best course of a action to repair a dual transistor pack

[@xraytonyb]

I think I covered this in several of my videos. I believe one of them was the SX-939 series.

[@littletraveller5428]

Do you do repairs for others too? I was thinking of getting a 1980 but had no one th could do it

[@MDFRESCUER]

Good video.

[@koumaraudio798]

Excellent video hope to see more. Can you make a video on how you made your matching pad?

[@lindseysteele1436]

I have a cr 820 that powers up hood but after it ets hot it shuts down can you help me with this problem

[@danielriley5083]

possible solder joint , dirty switch or control, relay? does it put out to speakers?

[@majkee1983]

What's the name of the blue tool You are using to setup the coils? I can't find it anywhere.

[@sweet01sv]

I have this same Pioneer SX-750 with the hum, safety switch triggers shortly after powering on. Would you be interested in a swap+$$ for your recently repaired unit? Or could I pay you to repair mine? Thanks. Great videos

[@xraytonyb]

I might be interested in doing something like that. I was going to post this one on eBay. If you are interested, send me a private message through my channel and I'll e-mail you back.

[@sweet01sv]

cannot seem to find a way to send you a private message through youtube. can you point me in that direction? thanks man

[@xraytonyb]

Just send me a comment in the discussion section of this youtube channel. I should be able to e-mail you from there.

[@grhinson]

They are snow pellets

[@lindseysteele1436]

Cr 820 yamaha

[@coreymelanson5139]

AWESOME JOB,U SHOULD BE LOADED RICH,...BEFORE YOU MAY THINK ABOUT UP-PRICING..CAN YOU FIX MY ASHLY CL-52E pro audio compressor/limiter? lol,prob cheaper to buy another,but it was beloved by me for many years. your great teacher,keep iy up. i learned lots,and some.day ill be brave and fix her myself. thank you for all you do. _COREY M.

[@ohboy4784]

About the transistors replacmen: . The fact that they are " better" like the technician says is totally irrelevant. In this circuit they are working with small signal,low current ,very low power condition. They are the differential input stage of the PA. The relevant issue is they are a matched pair on the same silicon die.(not just two transistors in the same "case"). That means same beta,same leakage currents,and same temp drift and need to have a high beta(if the new ones have 200 and the originals 400,that isn't good enough). If the transistors are not well matched, it will manifest itself in higher distortion of the unit. Since the technician didn't perform a distortion test(using a distortion analyzer and not his eyes) he couldn't see a difference. There should be a deterioration if a test is performed, preferably with varying the ambient temperature of the unit 0-40c. The counterfeit Chinese industry is a real problem. For obsolite parts,it can only be solved by buying substitutions from Digikey,Mouser and such original vendors.

[@metalmadnessSL]

Hello. I have a Pioneer Receiver SX 3700 wich have a high frecuency noise (Whistle) when i plug a turntable in phono or Aux section. i recap the power supply, Aux and Phono section but the problem still there also i check the grounding and conections from TT but didn´t find anything wrong. This is only present when i plug the TT other wise everything hear normal. maybe you can help with this issue. Thanks.

[@bobvecchi7981]

You never explained why your original diagnosis that the amplifier chip, as opposed to the prior filter, was defective. Being human, you, of course, are entitled to make mistakes, as we all do. But it’s important that we learn from those mistakes wherever possible. Your original assumption that the amp was bad was based on a very logical test that you did. But the failed filter before the amp grounded out the signal, making it appear the amp was faulty. Injecting the signal on the output of the amp did not manifest the same condition because the signal did not travel backwards through the amp to reach the faulty filter. If it had been able to do that you would not have drawn the wrong conclusion. The important lesson here is to realize that current, signals, will travel in every direction if allowed to and if there is a potential for it to follow. I would welcome your comments on whether my assessment is accurate or not. This way your other followers can be set straight as well.

[@RaulHernandez-lg5nw]

It's a ratio detector! Not a discriminator as you claim! You should learn the difference between the two!