Amp Repair - Troubleshooting an Intermittent Transistor

[@SevenFortyOne]

I bought one of these at a flea market in 1992 while I was still in community college that had the same problem yours does - a flaky/scratchy channel. I brought it in to the electronics lab and the lab tech that worked there showed me this trick. We found the bad transistor and determined what its part number was. At lunch I went to Signal Electronics (which was just off campus) and picked up a new one. We put the new transistor in and the amp started working fine. It was one of my most memorable learning experiences from college even though it wasn't part of any class. I only use it a few times a year theses days, but I still have the amp and its still working just fine - original caps and all.

[@jmcgatkinson]

A very detailed and thorough examination. I had a similar experience with an early 'Sansui' amplifier using a number of TO-92 (case style) small signal transistors in the tone control circuits. Many were 2SA.... prefixes, and one of them was so 'bad' that when I used the RX10 scale on my multimeter, the base-collector reading kept moving, as if there was some internal signal in the transistor in the unpowered circuit. Replaced them with BC549 and BC559 (PNP) low noise types. I wonder how many of these amplifiers were discarded due to this fault, with such inexpensive components to fix it...

[@mikemurphy5336]

the dc voltage on speaker that is dangerous for voice coil or protection cicuit, the solution to that is a 1 to 1 8ohm audio transformer to protect test speakers that you install in your bench area with test speakers , now dc voltage will overheat the transformer, instead of the voice coil and the transformer is 1000 times stronger than a flimsy voice coil in addition to this setup make an alarm circuit or relay circuit for transformer when dc is present !!

[@richardkelsch3640]

RIAA curve is simple. Too much bass on a record groove would make the grooves overlap. Since lower frequencies have a higher energy than the high frequencies, they record records with the opposite curve slope. This means the highs boosted and the bass cut. Therefore, when you play it back, you boost the bass and cut the highs. This has the potential of amplifying rumble, but it does lower hiss and high frequency noise in general, and thus a good trade-off as rumble is easier to mechanically fight and reduce than electrical hiss. The curve is scientifically determined to get the most dynamic range and frequency response from vinyl.

[@richardkelsch3640]

@Phil Allison Many receivers and pre-amplifiers back in the day had a "Rumble filter" that could be enabled. This usually was for the more expensive of equipment. Cheap stuff like Sanyo's never had a rumble filter. On the other hand, the speakers they offered never usually had sufficiently low bass response to matter. There were some specialized "Phono Pre-amplifiers" you could get with a rumble filter. However, instead of an electronic filter, you were best served making sure the turntable had an already incredibly low rumble output. The reason for this, was if the rumble output was too high, it could interfere with the cartridge's ability to reproduce the audio as rumble was creating intermodulation distortion. Seriously, if you needed a rumble filter, then it is highly likely you needed a better turntable anyway.

[@mdzacharias]

The tarnish on the leads of those 2SC869's is a dead giveaway on those, 2SC1345's, 2SC458, and many others. The tarnish works it's way into the body of the transistor, causes noise, leakage, various issues. Well known issue.

[@jamesmdeluca]

Greetings: You missed the opportunity of including the record outputs as part of the demonstration of diagnostic focus while attempting to show the narrowing of the faulty signal location. As soon as you learned the right channel was at fault, you should move the left channel probe from the left output to the right record output. When you beleved that the problem was on the right's main amp section you should use cold spray on the entire pcb to confirm your supposition. When the workspace gets tight, I suggest adding a bunch of narrow test wires as test points between stages. Great for monitoring DC level shifts with or without a source signal. The nature of your failed component should have been a significant DC level change. Just my two cents.

[@SinnerSince1962]

James, we all suggest you invest the time and energy to show us how to do it right.

[@johnlake6321]

Tony, like so many others, I thank you for sharing your knowledge in a (mostly) understandable way for those of us who are new to the hobby.

[@OnTheEdgeNow]

It would have been interesting to throw those transistors you replaced in a tester and see how they tested.

[@jaybats7865]

Great job. Your knowledge and skill is phenomenal and you must have every electronic testing device known to man. Thanks for the fun👍

[@SinnerSince1962]

Yank the boards and repopulate them. It’s time. Fixing just the problem leaves other ticking time bombs just waiting for next time.

[@R.AudioElectronics]

Tony another great video. Methodical and informative and also useful info on the phono device. Appreciate all of your insight on these vintage stereos

[@stevethompson7785]

PLEASE.... Repair and/or restore or even modify a Sansui QR 500

[@bernhardnizynski4403]

Wow - I have exactly the same model, which I purchased in 1973. I recently had some problems with the standby function. I don't know what the problem was, however, I opened it up and cleaned all the dust from the inside - it seems to be working OK. It may be time to check/replace all the Electrolytics?

[@davidgriffin79]

What was the music player sitting on the amp?

[@Tinybench]

Thank you very much for sharing your knowledge and experience! You do a fantastic job explaining and I appreciate it.

[@glenwhatley4125]

....also, it's just not wise to connect an amp that is known to go into dc offset sometimes to the dc rails as #1-the protect circuit isn't instantaneous and with loads connected will put undue stress on the relay contacts as well as #2 put undue stress on the output stage components in general. I've had transients like that cause an amp to go from a simple one intermittent drive transistor issue like you have here to then a complete blowup of that stage during those transient periods to max dc to dummy loads. Heat with hair dryer with no loads and use freeze spray first, then move to more intrusive methods if necessary is generally a safer method. Great videos!

[@anthonylovett1321]

Hi from mallorca spain .. Really enjoy your videos..especially as I own the SA8100 was a gift 35 yr ago.. I've managed to accompany it with a TX 7100 tuner CT 7271 cassette My 8100 also has this issue.. would you think the transistors you used would be compatible in my 8100...? I will be getting it looked at in a service shop.. Many thanks in advance.. Keep the great videos up..must take hrs to actually film n edit.. Regards Anthony

[@xraytonyb]

Yes, I believe they should work

[@jermcrow]

Great vid, always enjoy watching!

[@dhpbear2]

I'm wondering if it could be a resistor. Resistors can get intermittent too. Doesn't happen often, but it DOES happen :)

[@keithcoltron3171]

Hi Tony, you're fault tracing is second to none + you're teaching method is the same, there are some tech's that can and others that cannot! simply put watching you work is a real treat, many many thanks for your all time and efforts to teach everyone, I'm a tech but still enjoy you're work, I can do the work but explaining to others is the difficult bit, knowing how it's still great to watch.

[@xraytonyb]

Thank you for the kind words! I learn just as much from all of you as you do from these videos. Thanks to you as well!

[@MWHOME]

This is great. I'm having similar problems on my 1980 JVC R-S77 (60WPC). Not a lot of people want to touch them as they have some more modern stuff plus digital tuner etc... I want to narrow it down while I find a competent tech near me.

[@bgm1911]

Great explanation, thank you.

[@anthonylovett1321]

Hi there Gread comprohensive video.. I have been viewing you videos ..which are extremely helpful and interesting... I also have this amp..which to my delight I had forotton i had . I have not had this running for years ,and was suprised the unit actually worked... unfortunately i had the problem of the protection light staying on. I have now very carfully cleaned the pc boards free from dust etc ..also used contact cleaning spray on all the controlls... This seems to have fixed the issue.. unfortunately the orange power light next to the protection light is no longer lighting up ..which I cannot recalect weather it was working or not.. I have looked online but cannot seem to find a replacement.. Have you any idear where i can find this replacement part.. Most appriciated to anyone who can point me in the right direction.. Amazing videos so helpful from a true guro of amps. Anthony mallorca spain

[@johnnytoobad7785]

I just noticed that this amp. was featured in the HBO series "Vinyl" (along with a lot of other vintage 70's gear). Some of the in-wall audio gear set-ups were quite authentic. Of course it was shown with the power switch "on", but the pilot lamp off. My guess is that most of the gear used in the series was "non functional".

[@davidhigginbotham5451]

Nice Video. Chassis layout is strikingly similar to the Optonica SM-4545.

[@glenwhatley4125]

Very surprised you wouldn't heat up the output stage with a hair dryer and once it quit use freeze apray (affectionately known as 'Spray and Pray' to drop on each component to pin point the intermittent component. There would be no waiting for it to quit and no poking around taking the chance of shorting things out. Wonderfully informative videos.

[@MalteWilsen]

Excellent video, very helpful and interesting, too. THANKS!

[@g.fortin3228]

Pretty nice amp and great job explaining things. I need to learn how to hook up the scope for testing.. feel free to include those steps if the videos lend themself to the opportunity :-) Just learning here and appreciate your videos.

[@hansu-nihon]

Very helpful explanation for troubleshooting, very educational for me. Thank you!

[@cjnormin3582]

Great video but a shame you did not show how you replaced the transistors on the board, how did you gain access to them, did you have to de-solder all the connections and remove the boards. And how.

[@paullawless8901]

You should replace all of those 1451 I believe . Seemingly known problem transistors in the pioneer gear

[@chefbink61]

Great vid as always lots of good info!! Also I was wondering if you have ever messed around with a First Watt F-5 amp?

[@mrlejones]

Had the same pioneer amp! Was a great amp. Had it for years and it was used a lot. Gave it to my parents and they still have it though they don't use it much.. Great video.. Thanks

[@JelckedeBoer]

The Mr Carlson super probe would be a good tool to find these intermittent resistors. I build one and it works great.

[@vintagestereocollector4159]

Nice amp bro!

[@kennethiman2691]

Very helpful!

[@alexreeve]

That iRIAA gadget is cool.. i always done the same with software, but now i also want this ;)

[@davebrown3230]

I bought this model around 1974 to replace a new Rotel that I didnt like .

[@coreyfellows9420]

I've been looking for someone to work on some of my gear. Do you have a shop or a way I can contact you?

[@Twin_Flyer]

what software and hardware are you using to get the O-scope on the PC? Thanks!

[@jay_Pare]

I love your videos! Keep up the good work, you are really inspiring!

[@johnbaker6461]

My own 9100 is in the shop right now with the same symptom, intermittent protect mode. Very frustrating indeed. But I finally found a repairman patient enough to track it down, and I think he will have it back to me next week. I love this amp! As a vinyl guy, I concur that its phono stage is excellent - preferable, imho, to the Bellari stand-alone phono stage touted by Stereophile's Michael Fremer. And the 9100's headphone circuit outperforms (> 5 watts?) my Schiit Jotenheim. You can spend a lot of money trying to duplicate with high-end separates what this wonderful integrated amp does as a unit. It just sucks when it breaks down and you lose everything at once.

[@TY-ob7fz]

Hi John. My fix for that is purchasing an additional 9100 ( yes I have two ) and use the second unit to swap out the broken unit being repaired by vender. You'll always have a functioning unit. The intermittent protection relay can have many causes. In my unit was the protection circuit itself.

[@andrewfox1446]

Once again my friend a brilliant and informative video cheers.!!!

[@antraciet]

Easy fix but difficult to find. Good video, thank you.

[@petercornell2002]

Nice video Tony, thanks. Peter

[@DAVIDGREGORYKERR]

Just thinking that it might be possible to use BD131 transistors to replace the 2SC series transistors.

[@gearheadted9210]

very cool vid on troubleshooting thank you!

[@franciscorompana2985]

So wonderful I never get tired... Of the vintage hifi. Lol!

[@circuitmonkey6653]

And......THANK YOU! RIAA2 on order...

[@HipocratesAG]

Those 2SC1451 are the work the devil!

[@davidvigil7720]

Are you back to fixing?

[@tonychong1148]

Where to get the schematic diagram of this amplifier ?

[@georgebliss964]

Or just attenuate the signal generator via a 1K pot.

[@niafer9444]

I love the channel. Keep it up and good luck.

[@stephtronix1811]

Great video thanks!!

[@curtismuma1931]

Very nice. Thanks

[@andymouse]

I adore your vids ...cheers!

[@cristianofiorentini9165]

Che modello di pioneer è questo amplificatore?

[@anthonylovett1321]

Pioneer SA8100

[@911pep]

Good job .

[@bradsage7027]

Hey Tony , maybe this would be helpful info?, found this in the comments section of hifi engine. SA-9100 Amp Submitted by Jim McCann on June 10th, 2010. I used to service the sa9100's when they were new on the market. everyone ever sold had this problem - they would cook the output transistors (2sa679 and 2sc1079). it's the drivers (2sd358 and 2sb528). they overheat and short out and take the outputs with them. poor design. the coupling caps (.22/25v.) are also a problem. these should be changed. if you replace the drivers it will just fail again. We also found that when the power is applied the surge also knocks them out. the protection circuit also is a poor design. this amp does have very good specs when it is operating. we were a warranty station for pioneer back in those days and pioneer was always sending us parts for these. could put it on a variac and bring up the power slowly to prevent the surge. hope this helps Jim

[@Madness832]

What that music player that you connected (near the end)?

[@stephenbobby6715]

johnny cash

[@Madness832]

Not the song, the hardware.

[@jay_Pare]

Do you have a link for the iRIAA? Also, what are you using for dummy load?

[@82abn34]

www.haglabs.com on the iRIAA

[@fernarias]

Search ebay "inverse riaa". Since this is a 60 watt receiver, a 100 watt 8 ohm wire wound resistor (you'll need one for each channel) would work (about 10 bucks). Higher wattage amps would require higher wattage resistors, 200 watts are about 40 bucks and 300 watts are about 50. You'll also need a heatsink (I used a heatsink from a vintage receiver rated at 200 watts bought cheap and used from ebay)

[@fernarias]

These are mouser prices and there are much much cheaper chinese wire wound resistors on ebay.

[@petercornell2002]

hagerman-audio-labs.myshopify.com/products/iriaa2-inverse-riaa-filter Goes between the signal generator and the phono pre amp input

[@jay_Pare]

@@fernarias can I just go with let's say a 300 watts and use them with lower wattage receivers? Also, is the heatsink really needed? I thought 100 watts resistor were meant to dissipate 100 watts of power?

[@johnnytoobad7785]

It would have been a bit more informative if you showed the *removed* board when you were replacing the transistors. Also easier to see on camera. I knew a few folks that had this amp back when I was in college. Popular unit for its time. Good thing it had that protect circuit. It always helps to have a circuit to protect an amp from itself. I had an intermiitent transistor in a power amp once, it just made "popcorn" noise. Since I did not have a diagnostic lab at the time I just ended up selling the amp as a trade-in. Thanks for the RIAA info. I need to get one those "reverse adaptors" since I'm re-engineering an old RIAA pre-amp board.

[@TheTrueVoiceOfReason]

Have you ever come across the Claricon brand of stereo / quad reciever amplifiers? I have one and there's all but nothing out there on them. Everything I know is from my thread here: forum.nutsvolts.com/viewtopic.php?f=45&t=17042

[@caspianwendell]

What did you record this with? It’s extremely blurry

[@antraciet]

caspianwendell ; perfect here.

[@mrhuffler9791]

Perfect here too.

[@golfman9290]

The scope is from his laptop screen, but everything else is pin sharp.

[@caspianwendell]

Must have been KZbin, mine is clear now too

[@RaulHernandez-lg5nw]

What the hell are you talking about? The phono preamp circuit doesn't decode anything!! It's a downard slopeing response curve from low to hi frequency! The circuit boost the low frequency and attenuates the hi frequency! The amplitude output of a magnetic cartridge increases with frequency!