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Yamaha M50 Smoke - Help...

plresults

plresults

Active Member
Visited lady in her garage with equipment for sale. She plugged in M50 amp via extension cord. Protection light came on & went off. We started chatting about other stuff & maybe ten minutes passed - smoke out of amp. I know better and should have gone right into wall with cord. What I am I up against with that result? Dead transformer, a fuse, or something that can be rescued/repaired?

Now I am worried about the short (6 foot) long computer power outlet strips I used for my gear - are those things a bad idea?
 
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plresults said:
Visited lady in her garage with equipment for sale. She plugged in M50 amp via extension cord. Protection light came on & went off. We started chatting about other stuff & maybe ten minutes passed - smoke out of amp. I know better and should have gone right into wall with cord. What I am I up against with that result? Dead transformer, a fuse, or something that can be rescued/repaired?

Now I am worried about the short (6 foot) long computer power outlet strips I used for my gear - are those things a bad idea?
Click to expand...

You should build yourself a portable DBT so you can see if the bulb dims before you plug it into mains voltage so the magic smoke won't come out.


https://audiokarma.org/forums/index...ial-please-feel-free-to-copy-and-post.875584/
 
The M-50 can not be started on a dim-bulb-tester because of it's complex 2-stage power supply. Variac only.

The first thing to look at is to see if the paper-in-oil safety cap in the psu board burned. 0.47µF or 0.22µF depending on the model. Do not turn it on again and wait for Avionic to show up here.

Cheers,
James
 
avionic said:
Not a good idea.. With X-power Yamaha's .. Manual reccomends variac.
Click to expand...

I didn't know this and I don't have a variac yet.

So with a DBT if the bulb doesn't dim you know nothing is shorted, how do you use a variac for this and how do you know when to stop raising the voltage with a variac?.
Thanks
 
Orwell84 said:
So with a DBT if the bulb doesn't dim you know nothing is shorted, how do you know when to stop raising the voltage with a variac?.
Thanks
Click to expand...
No .. you could cause further damage. Monitor current draw.
 
avionic said:
No .. you could cause further damage. Monitor current draw.
Click to expand...

Thank you, I have much to learn still.

So using a variac you slowly raise the voltage while monitoring current draw and if it continues to draw current more than what the idle current should be you back off the voltage knowing there is a short somewhere?
 
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Bratwurst7s said:
The M-50 can not be started on a dim-bulb-tester because of it's complex 2-stage power supply. Variac only.

The first thing to look at is to see if the paper-in-oil safety cap in the psu board burned. 0.47µF or 0.22µF depending on the model. Do not turn it on again and wait for Avionic to show up here.

Cheers,
James
Click to expand...
Is that it in photos below? It’s on the board that sits between power and transformer.
 
upload_2021-8-1_15-48-44.png

C607 " across the line" Safety cap .22µf? 250v at least.
 
Just replacing the cap will likely be all that is needed.
 
plresults said:
Is that it in photos below? It’s on the board that sits between power and transformer.
Click to expand...

That's the nasty little thing alright. You got lucky that it only blew open. Sometimes they burn and take the whole board with them to Audio Hell. I saw your post just before going to bed and wanted to at least warn you not to turn on the amp again until more help arrived. I see now that it took Avionic 2 minutes to reply afterwards. Faster than the Fire Dept. :thumbsup:

Cheers,
James
 
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