Troubleshooting an intermittent weak channel - Pioneer SX950

Quick fix on the amp section of a receiver using only a scope, signal gen and dummy load.

[@denbofrancisco6958]

Tony is the man, the Master, and the repair magician. So glad to see someone out there repairing & restoring this never-to-be seen again vintage eq.

[@mdzacharias]

Speaker relay. Thump or tap on it while looking at the scope. You'll see it distorting and cutting out as you do. I don't remember if you serviced it before. Even if you did, they're prone to re-do's. Speaker relays are probably the most commonly overlooked area of service on older receivers which use them.

[@billmcdonald2436]

Excellent troubleshooting video for transistors Tony. I’ve been learning a lot about transistor radio repair from your videos.

[@1959Berre]

Merry Christmas to you and your family! Good health for all of you.

[@TY-ob7fz]

Tony. Thank you for that Xmas message. Please have a wonderful Christmas and a healthy and happy New Year. Be with family and friends and enjoy the holiday season, and as well said each and every day.

[@jdekong3945]

Merry Christmas Tony, all the best to you & your family

[@markhepburn4424]

Using Tony’s great videos gave me the energy to finally take on my old sx 950 ( I redid sx5580 basket case that had catastrophic failure, that I shelved for few years. Got it all working again. But wanted to pass on a problem that I fixed. After replacing the dc offset pots vr1/3 I could not get anything better than 180mv offset. Well the BOM, and docs list these as 1k pots. Well the schematic shows a 10k, and comparing with other similar circuits 1k is much too low. Using a 10k per the schematic fixed the problem . Just passing along a tip hopefully it helps if anyone else runs Into the issue.

[@jwl9286]

Great video! I'm a big fan of using troubleshooting techniques. Very well done. All your comments about the tendency of each component helps a lot! Enjoyed it. Thanks!

[@michaelbinning5010]

Great vid Tony as usual. Nice to see a vid with an Oscilloscope actually being used to troubleshoot an issue rather than another how to or demo vid with an expected result that you see in so many other channels. Thanks & Season's Greetings to you & family.

[@markadams1658]

Thank's for the kind Christmas message. All the best to you and yours.....My special gift under the tree would be for someone to explain the classic HK Citation 12. Both stock and NP mosfet versions. I'm weird like that. Merry Christmas!

[@alexreeve]

The mighty troubleshooting wood stick :) good job on tracking this down

[@harrymuhammad9835]

That was fun to watch...tight work sir.

[@CliveTrezona]

Nice repair Tony, thanks very much.

[@rolfts5762]

Thanks for very great video(s) Tony. Very interesting to watch and listen to your talks. ,,br from norway.

[@josephsirois2353]

I’ve used s can of computer duster spray held upside down in lieu of freeze spray , nice video thanks for sharing your experiences once again Tony👍

[@lanterno]

Thanks from the Celsius people

[@antraciet]

What a great video ! What i did before i watched it is making my own analysis and what i would do and i was spot on ! :-) I also would look at the transistors, tapping on things and use a freeze spray. I would also look to the connections, earth, etc...

[@robertcunningham1542]

Great video, one thing I assume you did but did not mention is that you should always check the bias and cross over after changing any transistor s in a direct coupled amplifier. Keep up the videos and have a Merry Christmas and Happy holiday.

[@vinha916]

love this video and very informative, thanks

[@1959Berre]

I always start troubleshooting by tapping the relay. If it is bad it is usually corroded or just dirty. I take it apart and polish the contact dots with a fine metal polish compound. Never with sand paper or any other abrasive tool or product. Coarse contacts will soon corrode again and retain dirt and oxides. If the relay is dead (burnt coil) I replace it with a high quality brand like Fisher. These relays come with a base from which they can easily be removed for inspection and maintenance without desoldering.

[@Groove1024]

really nice video as usually really interesting i learned something i was thinking of a bad contact but you already have check them in the last video about that amplifier thanks again... good repair store like you are going away now and they are what make old school things like this getting back for resist to 50 year again! i been on troubleshooting today too but it was for myself. i fixed my old Vorwerk vacuum cleaner. that is a really excellent cleaning device and even my 20 year old vacuum cleaner get the adaptor for the new generation carpet and sofa dry cleaning stuff and they provide parts for it! not a Apple rubbish :D

[@michaelbinning5010]

Forgot to mention Becker & Fagan with Michael Mc Donald singing chords, nice choice & one of my favorites.

[@russellhltn1396]

Just as a comment, most receivers I've looked at, the headphone jack came off the power amp, not the pre-amp. I'm sure there's at least one design out there like that, but without a schematic, I wouldn't make any assumptions.

[@taineasy]

Strange, I bought one of these in 1977 and am still using it daily after almost 45 years. NEVER had a problem with it and it still has the original front panel lights. My MARANTZ 2250 on the other hand blew up 20 years ago.

[@esnam6557]

Nice video thank you very much.

[@michaelaue7411]

Best video

[@AlexKnightVancouver]

Very informative video. I’m troubleshooting a strange issue with a Pioneer TX-8100 tuner. The capacitors don’t seem to be leaking and I’m starting to wonder if there’s a transistor issue. After running the unit for several hours, it gets very hot. Eventually the left channel starts to become distorted and the eventually dies. If I let the unit cool down, the problem temporarily goes away. It’s driving me nuts.

[@AmadonFaul]

xraytonyb do you have a recommendation on how to figure out what modern transistors to use to replace the ones in old equipment like this? Searching online all I find is a million suggestions for every transistor model. I've tried matching the power dissipation, C-E max and gain but then if I look at the recommended replacements their gain is never the same as the specs on the original. How do you figure out what to use? Thanks!

[@LuisSanchez-bd1xu]

Dear Tony how are you, I hope everything´'s going well. I want to know if you can help me with a doubt, I'm in the same situation you show here. I recently review the AUDIOKARMA page, and a lot of people says, that the correct replace for the A726, is the KS992, but KS992 is out of stock in Mouser, Digikey, etc. Someone post that the BC327 could work fine, and those I have in stock, what's your opinion? Regards.

[@kennynvake4hve584]

How do you find, or know where, to put your scope on the preamp? My very first guess, is the output transistor, or transistors, or the driver of them, is either got a bad solder joint, or they are failing...Im at 13:40 in the video and have watched it before...

[@cat-lw6kq]

go to Amazon.com and get the book "Transistor Audio Amplifiers by Jack Darr" He shows how to troubleshoot an amp with the Oscilloscope.

[@kennynvake4hve584]

A nice thermal camera would help out alot...to locate the hot spots..

[@michaelaue7411]

Tony is that a leaking cap just to the left

[@taineasy]

What replacement did you use for the 2SA726's?

[@LuisSanchez-bd1xu]

KSA992 I use it without problem, just check they must be gain matched.

[@johnsweda2999]

Wonder what these dots are they put on! What's the point of the Blue dot. Can you find out the balance just using a multimeter and checking the resistance of the transistors to balance them

[@xraytonyb]

I believe the dot code was used to indicate the gain or beta range of the transistor. I think Motorola was the first to use it. By picking two transistors with the same color dot would indicate that you have a similarly matched pair. I think Yellow was low gain, green medium and blue high, but I'm not sure. Not a lot of info out there about it because you only saw this in factories or production lines. Anyway, that's what I was always told, but I might be totally wrong, so take it for what it's worth ;)

[@BobWilson84]

Pegggggggggggg. I troubleshoot to Peg and Aja all the time :)

[@xraytonyb]

One of my favorites!

[@domenicoorefice7269]

hello, I am writing to you from Italy, I am a Pioneer lx90 owner, my beloved amplifier has a problem, the lcd display fizzes continuously, how can I solve the problem? thanks Domenico

[@reynir8448]

bc557 is a good replacement for 2sa726

[@fernarias]

That's a general transistor. You need low noise in the audio path.

[@reynir8448]

every european amplifier have used bc557 in signal path have you repair amps

[@fernarias]

Yes, I have. I have been doing it for 7 years and own too many amps, tuners and receivers(learned electronics in the 80s although I became an accountant). Don't have any experience with the BC557(I'll have to try it out). The recommended transistor for the 726 is the ksa992 although I prefer the ksa733 or the ksa1015 depending on application. When I started I only replaced the caps but now I also replace transistors, diodes and rectifiers (have noticed that the Germans do the same plus they also do resistors). I've noticed a lower noise floor than even original (old enough to have heard them in the 70s). Watch Tony for the FM alignments and have started to study the electronics behind them (books from the era vs. internet). Just so you know, I look up the BC557 specs before I answered your post. Not being malicious at all. The datasheet I found said general transistor.

[@MrPageplayer]

Are you on Patreon? I'm making monthly pledges to Mr Carlsons Lab and would do the same for you if you were on it. I love your channel since you're geared more to my interests, being Pioneer receivers. Just bought a sx-850 for my first project!

[@pvb9964]

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