Vintage amp repair - 01 Left channel not working

I finally managed to fix the issue :o)
see the solution here in part 04 of the repair:
kzbin.info/www/bejne/qIeriIqsr7ejjrs
Previous description: I have a beautiful Marantz pm 350 which has just gone faulty today, it started overheating, I turned it off and let it cool. After powering it back on, it has a hum on the left channel instead of music (Right channel works perfectly). A component has clearly blown.
Watch the video for more details... If you know what the problem is please comment and get in touch. I'm not going to give up on it and I will be making a video of the repair and success in case others are having the same issue...Positive thinking! :o)
No copyright infringement intended

[@MsMadLemon]

Just to let you know, this video is very old and I already fixed this amplifier and have learned a lot since. Thank you for your efforts to help me. here is a follow up video on this for more info: kzbin.info/www/bejne/qIeriIqsr7ejjrs

[@cedricbaudry330]

Ok no problems i haven't seen the date , i like to help if i can , good continuation for you , i see yours videos now .ciao

[@waing3360]

It seem that it was some kind of soldering problem, it will finally burn up transistors, you need to take the main board and measure all power and bias transistor s, replace it when needed

[@vintageseller7700]

Nice to see a girl have interest in electronics to this extent. Kudos.

[@moundofsound4768]

Girls and complicated electronics??!! surely not. And she knows what a condenser mic is! whatever next!

[@gustercc]

moundofsound can’t tell if you’re being supportive or....???

[@LewieLeway]

@@gustercc He's taking the P out of Vintage Seller who sounds like a vintage item himself. A patronising male chauvinist.

[@jbtvt]

@@LewieLeway Male chauvinist? What a dink you are. The original post was giving her a compliment. "Nice" and "kudos" = positive reinforcement. Very few girls or women are interested in electronics. Almost 90% of EE degrees go to men. She's breaking the mold and going beyond comfort levels that very few women will explore. And yet somehow, to the modern leftist, even acknowledging that there are statistically significant interest and ability differences by gender is heresy, and paying someone a compliment is patronizing. You are absolutely pathetic. Unsurprising to see the "s" instead of "z" - typical British/Australian beta male. Alluding to statistical facts instead of PC newspeak, unacceptable! "Because it's [current year]"

[@Competitive_Antagonist]

@@LewieLeway Sure it sounds patronising, but I'm not sure it was made from an ideology of male chauvinism. He made a compliment about her having an interest that doesn't align with traditional gender roles. There still are some real chauvinists from traditionally male fields, that would be a lot less welcoming than him.

[@robinsonsoto8471]

DC in getting into the audio stages. INSPECT THE BOARD CAREFULLY. Check for leaky Capacitors, Take either audio Tracer or Scope and follow the signal.

[@dedskin1]

Its easy. You have 2 circuits, stereo output . From one you get current where there shouldn't be one , and the other is ok. So you can change components like you did for transistors , and see if anything changes . its a long procedure , so you can check with your voltmeter where is one channel getting voltage and the other doesnt have it or its smaller . thats where the problem is . If you get -V , change the leads . There is no such thing as -V. there is just potential or there is no potential, negative potential does not exist , the least amount of potential a body can have is 0. But we dont know how it all works , so we invented Holes , like black holes . A spot in space where matter is pulled too. Same for positive voltage . positive voltage is presence of holes , negative voltage is electron build up. Current flows from positive to negative in theory. In reality its the other way around cuz only real thing there are electrons . So you have electrons flowing through your speaker wild , it probably means shorted cap. Caps are used to limit the flow of electrons , also OP amps should not generate any current , they can do that if they have excessive voltage on input or bad components around it . But its reasonable to say that you have one shorted cap generating excessive electron flow , and that burned OP AMP or something else . You have 2 problems , one forced the AMP output flow to go to 0( speaker turning down) and then when you turn it on again, OP AMP is blown and its inducing current where there should be none . Resulting in flow of wild electrons across the speaker and bad biasing of transistors .( hum on your speaker ) Transistor wont let the current go in opposite way if they are not bipolar . and those power transistors are not . so the electrons are coming from emitter and going back to base so you have -40v on base where there should be +0.33V, meaning instead small number of electrons going in correct way you have large number going back. Resulting in PSU hum on speaker . It all comes down to caps , small ones .. .but they burned something else when it happened . so youll find the problem on AMP input , and PRE AMP output , somewhere between that is also connected to a switching circuit. You can test this by using head phones . cuz PRE AMP output is used for powering head phones . If there is same thing going on there , for sure the problem is in BAD PRE AMP capacitor& OP AMP.. You are stuck cuz you are tracing problme in power AMP and its not there , its in PRE AMP circuit, but that could have caused AMP circuit to go bad also. Hope i helped with my limited knowledge and that everything is correct

[@MsMadLemon]

+Pavle Pavlovic actually I wouldn't call that limited knowledge, you're being quite in depth here. Thank you! I tested the output at the preamp stage and all seemed fine, there seems to be a signal coming through, the power transistors are fine but it's the main amp which seems to have the fault in it, if you watch the third part of this here: kzbin.info/www/bejne/j52kZIF9p7mGl5Y You will have more of an idea as i've narrowed things down. But thanks again for your feedback as i'm going to learn more about the issue with the info you've given me!

[@Badassvidsz]

Pavle Pavlovic : The best and the most appropriate thing is to take our hi-fi machine to a technician to find the problem and fix it of course ... not to put our fingers inside the machine when we don't have the appropriate knowledge The only and most pissible thing we are about to do is to make things even worst than they allready are

[@juanitobraceras]

I have a PM350 also and when I turn on instead of only the green light in the middle all the lights are on and the speaker they don't sound. Seems like a overpower problem? Do you have any idea how could I solve it?

[@animishaalagappa2327]

A channel of my stereo had a similar problem after I switched the mains off while it was running. Now, a channel output terminal has no power output. Any suggestions for a DIY fix during lockdown?

[@richardhylton8296]

Sometimes cleaning works if there is some oxidation on controls.

[@karlkuttup]

sounds like caps gone or a short as well does it have an external ground at the back of the amp

[@wizardx4187]

BANG!!!!!!!!!!!!!!!

[@SoddingaboutSi]

You have DC on the output. There is probably a shorted driver. Check the DC component on the speaker terminals. I would disconnect your speakers as it will ruin then!

[@MsMadLemon]

+Simon Spiers I've finally managed to fix this amp and uploaded the fix here: kzbin.info/www/bejne/qIeriIqsr7ejjrs Thanks for the help by the way! :o)

[@moundofsound4768]

I had the same amp once upon a time. same issue. wish i'd of kept it.

[@chickenfoundation9323]

My kenwood km 206 power amp would hum only when the rcas were connected, turns out the rca input jack wasn’t grounded because the ground solder pad lifted

[@stellagorinov246]

MsMadLemon what speakers do you use?

[@MRDEEPAKVASWANI]

you are too cute ,watched your video because i have somewhat the same issue

[@luisvilleza2687]

Is that fluke 77 ?

[@1rosefly]

I have a amplifier thats a realistic mpa 100 and its very old and both channels stopped working

[@waynehennen4358]

Great video-2 thumbs up-thanks. I hate those pop up ads.

[@LtdBoomer]

The Fuses MUST be ok,because the Amp was running,with one faulty channel.with blown fuses there will be nothing!

[@MsMadLemon]

That depends on the amp. I had a fergusson amp which had a fuse for each the left and right.. The left blew and stopped working. The right still worked. Basically ended up with the same issue as this.

[@레오-v2g]

I guess that C401~404 capacitors is problem.. wasn't it?

[@george34777]

your voice sounds like music in my ears....

[@cedricbaudry330]

Hello, You must start to clean with Deoxit all the potentiometers , all the rca jack with steel wool , if the problem stay , maybe its a masse problem or the drivers . Hope you have find the solution . I am french and i don t write english very well sorry for this . Bye

[@MsMadLemon]

This is so old, one of my first videos from 3 years back, I already fixed this and learned a lot from it, thanks for the help though :o)

[@420gramas7]

Just give this amp to experts service and they will fix it :) I think it could be blown driver stage transistor or power transistors. You can check them with multimeter and if you found a bad one unsolder and test it again.

[@MsMadLemon]

+Ramas Ramzetti Thanks Ramas! :o) The experts will be a last resort. I will first troubleshoot it starting with replacing the capacitors, I have most of them already. I have managed to find the full service manual including components list and circuit diagrams, that will make things much easier, thank you for shedding some light, I will test the transistors next :o)

[@MsMadLemon]

+Ramas Ramzetti Yay! I fixed it :o) kzbin.info/www/bejne/qIeriIqsr7ejjrs

[@MaestrroMusic]

I guess that it is exactly the same with headphones plugged in?

[@MsMadLemon]

+Daniel Mitchell Yes, actually my third video goes into more depth about this, I know where abouts the issue is, just cannot pinpoint it further: kzbin.info/www/bejne/j52kZIF9p7mGl5Y

[@charliew1938]

Your speaker is blown

[@MsMadLemon]

It was a blown transistor. Replaced.

[@uvb74]

Esse aparelho é chato pra trabalhar com ele

[@Desuetus]

This isn't a repair.

[@MsMadLemon]

ok