Smoke from M-70 what to do? :(

mr_RBG

mr_RBG

Well-Known Member
I was listening my M-70(not loud) and heard popping/clicking sound from the speakers. I ran to turn the amp off but by the time i reached it it was covered with smoke. I removed the cover and found that 250v 0.22uf rectangular plastic capacitor in power supply was burned and cracked(it was the smoke origin). I attached a photo of the cap. What capacitor should I use to replace? Is there any way I can check or try to find the problem without switching it on? Can it be just the cap or something more serious happened? I would really appreciate any advise! Maybe this is a common problem. Thanks in advance?
 

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That's the main AC line suppression cap. Don't F**K with it. Replace it. Problem solved.

Any "X2" cap of the same rating will do nicely. There are a couple smaller ones in there as well.

This is a well documented issue with the M-70. There was a 220V recall bulletin issued for world units, but we've seen trouble from them all.
 
Thanks a lot! :) Sorry, but what is a "X2" cap? Can I replace it with WIMA Polypropylene Film Capacitors 630V .22uF 5% (sorry if it is a total nonsense)?
 
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X2 is a class of film suppression caps made to operate safely with spikes as high as 2.5kV in high voltage AC circuits. I like using WIMA caps, but I don't think you'll find the proper fit in this application. Because the rifa cap was oil impregnated paper, hence the prolific amount of smoke, it's likely to be larger than what you'll find in a newer film-foil X2 cap.

More good info here: http://my.execpc.com/~endlr/line-filter.html

This might work, I don't recall the lead spacing and you need to be mindful of it when using these box caps that fit tight to the board. http://www.mouser.com/ProductDetail...=sGAEpiMZZMvQAn3cSZoTr/E8oegrb5rTfpxeh9z1Tls=
 
Russ's panasonics maybe a better selection.Due to longer leads lengths.
Check your lead spacing..:yes:
 
Thank you fellows!

I was thinking... if i am going to order caps from mouser, maybe it is time to re-cap the whole amp. I always use the same to original value for capacitance, however I found that many people suggest to increase capacitance of the big cans, Why? Can you do it? And bypass them with film caps. Would it be a good idea? Or just replace them as I usually do.
 
Larger filter caps create a larger sink source for the power demands. Too large can put a strain on an otherwise already pushed power supply. The rectifiers need to be up to the task. Given the difficulty in sometimes finding the proper physical size, stepping up as much as 20% is OK. Much larger than that and you risk stressing the rest of the power supply. Unfortunately for another Mouser customer right here, the best solution for filter caps often turns out to be the Panasonic THA series snap-ins available at Digikey. Line up the right pins and trim the others off.

If the amp doesn't already have bypass caps, I install them. ~.010-.020% of the value of the filter cap in a film is a good rule of thumb. If you have 18,000uf caps, a 2.0uf or 2.2uf 250V film cap works well.

Don't forget the (4?) little Y caps on the AC board as well, 4700pf as I recall. Those were tougher to find right-sized.
 
Well I read the manual, and it has a protection circuitry build in. Why didn't that kick off? Or should a fuse have blown to protect the amp against fire?
 
ouimetnick said:
Well I read the manual, and it has a protection circuitry build in. Why didn't that kick off? Or should a fuse have blown to protect the amp against fire?
Click to expand...

:no: Thats why Yamaha had a recall on amplifiers with the X-power supply. That cap is on the input AC control circuit. On the schematic look at C607 I believe . Then look at the input line fuse. If that cap shorts internally it will burn open before the fuse does.Specially the old oil RIFA's that were OEM.

Yamaha Recall notice
http://www.whathifi.com/News/Yamaha-issues-safety-recall-on-amps-30-years-on/

Even though the recall was on the 220-240 volt models. The 110-120 models still pop once in a while.Same reason...I don't imagine the damage on the 120 volt models is as quite as severe as the 220 models.
 
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Depends on what the ceramics are there for but I would leave them alone. They are often used in high frequency applications and doing what the designer intended. IMHO, if Yamaha wanted film caps there, they would have used them.

Replacing very small lytics in the signal path with film if you can squeeze them in makes sense. Replacing tants with low noise lytics makes sense. Replacing ceramics is not advised because they're probably in there for RF noise suppression.

Post the schematic and indicate which caps you are looking at. Maybe one of the real circuit guru's can weigh in.
 
That cap is a pattern failure on M50s, M70s and possibly other Yamaha amps.
If you have one of these amps, replace it now. It WILL smoke. And it stinks up the whole amp.

I like it cause when it smokes, the owner sells it cheap! And those amps are worth having.
 
Thank you!
I've read about X and Y caps. However, I couldn't find anything but "Metallized Polyester Suppression Capacitors" on mouser.com, no marks if its X or Y. Can just choose one of these Suppression Film Capacitors and use it as Y type?
 
I've seen such failures on vintage equipment, even on a Revox B795 turntable that consumes very little power.

In every such case the AC fuse was also blown and nothing else was affected. But the unit won't power up after that, simply because of the blown fuse. If you try to replace only the fuse it will blow again (don't try that).
 
Yep, but I did not want to replace just a fuse, I will recap all unit.
BTW, brutal, avionic, do you remember how to reach the power supply caps and LC 72780 board? I unscrewed everything there... :)
 
I do believe you have to desolder a 5 pin board-to-board connection after removing the front panel.You'll see what I'm talking about as soon as you swing the front plate down.
 
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mr_RBG said:
Sure, thanks! I thought maybe there is more elegant way to do it.
Click to expand...

Oh there is!!!:yes: But would cost you a labor charge more than likely,If somebody else does it...:D
 
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mr_RBG said:
Thank you!
I've read about X and Y caps. However, I couldn't find anything but "Metallized Polyester Suppression Capacitors" on mouser.com, no marks if its X or Y. Can just choose one of these Suppression Film Capacitors and use it as Y type?
Click to expand...

Read the data sheet if in doubt. The big cap needs to be rated an X2 rated safety cap.
 
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