What would cause a transformer in a power supply to fail? - AVS Forum
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post #1 of 27 Old 01-13-2010, 06:03 PM - Thread Starter
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I am receiving my Yamaha RX-V765 after being serviced and they replaced an open transformer in the power supply. I was having an issue with a buzzing/humming noise that would come about when the receiver would warm up. I have no knowledge about the inside workings of a receiver so I was hoping someone could tell me what would cause a transformer to do this?
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post #2 of 27 Old 01-13-2010, 06:08 PM
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Quote:
Originally Posted by Urlacher5454 View Post

I am receiving my Yamaha RX-V765 after being serviced and they replaced an open transformer in the power supply. I was having an issue with a buzzing/humming noise that would come about when the receiver would warm up. I have no knowledge about the inside workings of a receiver so I was hoping someone could tell me what would cause a transformer to do this?

So they replaced the old one huh? It's possible the transformer winding somehow got damaged. The question is how? Did it suddenly start humming one day or was it a gradual thing?
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post #3 of 27 Old 01-13-2010, 06:18 PM - Thread Starter
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Yeah they replaced the transformer, the receiver is only 6 months old. It definatelly wasn't a gradual thing because my hearing is super sensitive and I would have noticed it.
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post #4 of 27 Old 01-13-2010, 06:35 PM
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Quote:
Originally Posted by Urlacher5454 View Post

Yeah they replaced the transformer, the receiver is only 6 months old. It definatelly wasn't a gradual thing because my hearing is super sensitive and I would have noticed it.

I would guess that the transformer was bad to begin with. It's unfortunate, but it does happen occasionally.
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post #5 of 27 Old 01-13-2010, 06:49 PM
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I would like to know too. I bought my Yam 765 in June and it died in September - it wouldn't power on and I also had the buzzing sound in my left back speaker . I just got it back but I put it in the bedroom in a 5.1 setup so I don't know if the buzzing was fixed. I bought a Denon 3310 when the Yam died.
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post #6 of 27 Old 01-13-2010, 06:54 PM - Thread Starter
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Originally Posted by MAGHUNTER View Post

I would like to know too. I bought my Yam 765 in June and it died in September - it wouldn't power on and I also had the buzzing sound in my left back speaker . I just got it back but I put it in the bedroom in a 5.1 setup so I don't know if the buzzing was fixed. I bought a Denon 3310 when the Yam died.

Our problems are different as I didn't have buzzing in the speakers, just the unit itself was buzzing.
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post #7 of 27 Old 01-13-2010, 06:56 PM - Thread Starter
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Originally Posted by croseiv View Post

I would guess that the transformer was bad to begin with. It's unfortunate, but it does happen occasionally.

Yeah thats what I was thinking. I didn't think I was doing anything wrong to cause this. I have all my electronics running through a APC H15 power conditioner so I knew it couldn't have been a power issue.
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post #8 of 27 Old 01-13-2010, 07:27 PM - Thread Starter
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My receiver was serviced at United Radio in East Syracuse New York. Does anyone have any experience with this company? They are supposed to be really good.
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post #9 of 27 Old 01-13-2010, 07:41 PM
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Transformers usually fail due to a defect in the manufacturing process (and very rarely due to a design defect). Since CE transformers are (usually) machine wound, it is always possible to get an undetected defect in the coil wires, that can result in transformer failure. There are other manufacturing steps that can result in a transformer that "buzzes", but those are usually caught during unit checkout. The faults that cause "buzzing" may, or may not, result in failure.

I have performed failure analysis on a spacecraft qualified and tested transformer that failed, after well over 500 hours of operation, during the pre-launch checkout tests (fortunately). The failure was caused by a wire that was slightly kinked during the transformer coil winding process (plus an error in the winding layout).

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post #10 of 27 Old 01-13-2010, 08:04 PM - Thread Starter
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Quote:
Originally Posted by CT_Wiebe View Post

Transformers usually fail due to a defect in the manufacturing process (and very rarely due to a design defect). Since CE transformers are (usually) machine wound, it is always possible to get an undetected defect in the coil wires, that can result in transformer failure. There are other manufacturing steps that can result in a transformer that "buzzes", but those are usually caught during unit checkout. The faults that cause "buzzing" may, or may not, result in failure.

I have performed failure analysis on a spacecraft qualified and tested transformer that failed, after well over 500 hours of operation, during the pre-launch checkout tests (fortunately). The failure was caused by a wire that was slightly kinked during the transformer coil winding process (plus an error in the winding layout).

Well thank you for your detailed explanation and expertise. Coming from someone with experience puts my mind at ease that chances are it wont happen again.
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post #11 of 27 Old 01-13-2010, 09:15 PM
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Quote:
Originally Posted by Urlacher5454 View Post

My receiver was serviced at United Radio in East Syracuse New York. Does anyone have any experience with this company? They are supposed to be really good.

The Yamaha AVR power transformers have an internal circuit breaker that is
required by UL/CSA. If the transformer gets too hot then its purpose is to open to protect the AVR from self-destruction...
I recall its temperature threshold was set @ 75 degrees C.
Note that circuit breaker is not servicable, as the entire power transformer must be replaced.

We have stated on AVS many times the importance of ventilation for the AVR, one should have at least 3-4" open air space around the AVR L/R sides and top. Also it is documented that the lower price-point Yamaha AVRs have certain thermal design limitations especially if driving low impedance/low efficiency loudspeakers.

Just my $0.01..
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post #12 of 27 Old 01-13-2010, 10:53 PM
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M Code -- That's interesting, and very unusual. That means that the transformer can quit, without actually failing (open circuit breaker, only). Since excessively high temperature is the primary cause of electronics failure, they may chose to do that to protect the rest of the electronics in the units. Using a non-resettable thermal breaker is unusual for Yamaha equipment (which I have always associated with quality designs).

Setting the temperature limit to 75 degrees C is very low, for a transformer. Commercial measurement equipment, for example, have operating temperature ratings on the order of 80 to 90 degrees C (IIRC).

A temperature of 75 degrees C is 167 degrees F, which is very hot, though, for home electronics. But, as you said, it does point out the need for good ventilation around AVRs (and I've seen pictures of some installations that make me shudder -- 2" or less over the top of an AVR). If the power transformer is running near 75 degrees C, the power amps (transistors or FETs) have to be running over 100 degrees C, which is way too hot for reliable operation.

My Pioneer AVRs have always stated that they need at least 12" to 18" of clearance over the top of their units (they don't use cooling fans). With adequate clearance, they run very cool (relatively).

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post #13 of 27 Old 01-14-2010, 04:23 AM
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I have also read about thermal breakers buried in transformers to prevent catastrophic failure.

I know most (many?) receivers also have a thermal shutdown feature for general use. And I believe most (many?) have over current and/or over voltage shutdown.

One question I have had, and I have not found anyone who knows the answer is what limits power in most receivers. Voltage drop from the transformer, or limiter circuits? If you look at power vs distortion curves in reviews where that was tested, you will see a point where distortion sharply increases in via a fixed slope. Some reviews have claimed that's due to a limiter circuit.

If there was not a limiter circuit limiting power, as you increased power, I would think the transistors, being driven with more input, would present a lower impedance to the transformer secondary, and, as that gets closer to the transformer's secondary's own internal resistance, you would get a voltage drop. At that point, I would think high current flow through the windings would start to heat up the wiring.

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post #14 of 27 Old 01-14-2010, 04:52 AM
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Quote:
Originally Posted by Urlacher5454 View Post

My receiver was serviced at United Radio in East Syracuse New York. Does anyone have any experience with this company? They are supposed to be really good.

FWIW, they seem to be the regional authorized Marantz repair center, too -- at least that's where the local A/V store sent my NR1501 for an in-warranty firmware update. They're taking forever with it, though, claiming that they're waiting for a part from Marantz.

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post #15 of 27 Old 01-14-2010, 05:24 AM - Thread Starter
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Originally Posted by Selden Ball View Post

FWIW, they seem to be the regional authorized Marantz repair center, too -- at least that's where the local A/V store sent my NR1501 for an in-warranty firmware update. They're taking forever with it, though, claiming that they're waiting for a part from Marantz.

Same with me, it took them a week to get the part in but as soon as they do they put your repair at the front of the line.
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post #16 of 27 Old 01-14-2010, 02:22 PM
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Quote:
Originally Posted by CT_Wiebe View Post

M Code -- That's interesting, and very unusual. That means that the transformer can quit, without actually failing (open circuit breaker, only). Since excessively high temperature is the primary cause of electronics failure, they may chose to do that to protect the rest of the electronics in the units. Using a non-resettable thermal breaker is unusual for Yamaha equipment (which I have always associated with quality designs).

Setting the temperature limit to 75 degrees C is very low, for a transformer. Commercial measurement equipment, for example, have operating temperature ratings on the order of 80 to 90 degrees C (IIRC).

A temperature of 75 degrees C is 167 degrees F, which is very hot, though, for home electronics. But, as you said, it does point out the need for good ventilation around AVRs (and I've seen pictures of some installations that make me shudder -- 2" or less over the top of an AVR). If the power transformer is running near 75 degrees C, the power amps (transistors or FETs) have to be running over 100 degrees C, which is way too hot for reliable operation.

My Pioneer AVRs have always stated that they need at least 12" to 18" of clearance over the top of their units (they don't use cooling fans). With adequate clearance, they run very cool (relatively).

EZ to understand..
The power transformer is the single most expensive component within the AVR, and Yamaha (and other brands) have made the decision to slim down the transformer to save $...

Note that the AVR mite still put out the rated power as the brand will simply add more windings but of a thinner guage copper..
End-result is that the transformer will saturate sooner when pushed hard and then its output will sag..

Yamaha in its lower priced AVRs (SRP <$999) are not considered a high-current design, as for the last 3 generations they have been purposely been limiting max available power supply voltage. Additionally things like output device specs have been decreasing as well as heat sink area.. Therefore as the power amplifier circuit is pushed hard driving lower impedance speakers, all of the related components/circuits start to heat up and it then the temperature increases very rapidly. Also as previously mentioned, the warnings about air circulation are usually ignored..

Regarding the internal thermal fuse within the power transformer this is a mandatory UL/CSA requirement. However since power transformer has been sized down it is more likely for the thermal fuse to become open...

Keep in mind..
Certain materials such as copper (transformer), steel (transformer, chassis), aluminum (heat sink) have tripled in price over the last 2 years..
Yet some consumers still expect the price of AVRs to decrease like PCs so the brands try to slim down on internal components cost..

Just my $0.01..
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post #17 of 27 Old 01-14-2010, 07:58 PM - Thread Starter
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Ok I got my receiver back today and guess what? I still have the hum. It's a faint hum/buzz but I sure can hear it. The weird thing is that if I put my hand on the case it goes away. It's like the top of the case by the vents is really thin and it's vibrating. It's dead silent when I put my hand on it. What gives guys? Is my hearing just too sensitive?
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post #18 of 27 Old 01-14-2010, 08:16 PM
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Quote:
Originally Posted by Urlacher5454 View Post

Ok I got my receiver back today and guess what? I still have the hum. It's a faint hum/buzz but I sure can hear it. The weird thing is that if I put my hand on the case it goes away. It's like the top of the case by the vents is really thin and it's vibrating. It's dead silent when I put my hand on it. What gives guys? Is my hearing just too sensitive?

Sounds like the transformer's mounting is loose. Pop off the top and titen securely the transformers mounting screws to the chassis, also if the transformer assembly has screws holding it together titen these as well.

Just my $0.01...
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post #19 of 27 Old 01-14-2010, 08:23 PM - Thread Starter
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Originally Posted by M Code View Post

Sounds like the transformer's mounting is loose. Pop off the top and titen securely the transformers mounting screws to the chassis, also if the transformer assembly has screws holding it together titen these as well.

Just my $0.01...

I could do that if I knew how to open the thing up and knew where to look for the transformer. Can you provide a little help?
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post #20 of 27 Old 01-15-2010, 08:39 AM
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Quote:
Originally Posted by Urlacher5454 View Post

I could do that if I knew how to open the thing up and knew where to look for the transformer. Can you provide a little help?

OK..
Hopefully you are mechanically inclined..

Disconnect the AVR, the top cover is held on by several philips screws including sides and back. The power transformer is the bigger square device close to where the main AC cord goes in. The transformer is held down by flanges with a screw in each corner make sure these are torqued down tite. Next the transformer itself may have horizontal screws holding the assembly together, these should be titened as well. Be careful not to disturb any of the wire harnesses or connectors..

Just my $0.01..
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post #21 of 27 Old 01-15-2010, 08:58 AM
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Whatever you do, unplug the receiver before going anywhere near the power transformer. You are in the lethal voltage section. The caps could theoretically hold a charge as well. I recall reading that they often put something in the circuit to auto drain the power supply caps. But I don't know how long it takes for those to drain.

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post #22 of 27 Old 01-15-2010, 04:02 PM - Thread Starter
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Thanks guys for your instruction. I think I am going to take a stab at tightening up the screws. How long does the unit have to be unplugged for all the power to be out of it?

As I said the buzzing is very faint but audible. However, you can't hear it when i'm watching tv or a movie. If I change my mind and not do anything and ignore it can any malfunction happen because of this down the road? Thanks again guys.
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post #23 of 27 Old 01-16-2010, 10:59 AM - Thread Starter
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Yeah i'm feeling confident...I think i'm going to give it a go in the next few days. I hope tightening some screws will solve the problem, I would hate to have to send my receiver out for service again.
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post #24 of 27 Old 01-23-2010, 05:27 PM - Thread Starter
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*Update* I sent my receiver to the service center and they checked the receiver again and they say there is absolutely nothing wrong with it. They could not duplicate the noise I was hearing, in fact the head technician took it into a conference room they have in the building and he said he could not hear a peep from the receiver. I also asked him to see if all the screws were tight around the transformer and everywhere else and I guess they were. So i'm not sure what i'm hearing and why I can make that noise go away my putting my hand on top of the case.
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post #25 of 27 Old 01-24-2010, 07:30 AM
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Well, it could simply be that your hearing is more sensitive than that of their head technician: he's bound to be older, and older people tend to have developed hearing deficiencies over the years.

If it's still there when you get it back, and putting your hand on it makes it stop, well, you might consider putting something on top of the receiver (avoiding blocking the ventilation holes, of course!).

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post #26 of 27 Old 01-24-2010, 05:18 PM - Thread Starter
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Quote:
Originally Posted by Selden Ball View Post

Well, it could simply be that your hearing is more sensitive than that of their head technician: he's bound to be older, and older people tend to have developed hearing deficiencies over the years.

If it's still there when you get it back, and putting your hand on it makes it stop, well, you might consider putting something on top of the receiver (avoiding blocking the ventilation holes, of course!).

I'm going to be getting a small fan to help with coloing and it has rubber feet on the bottom, I wonder if that will do the trick.

Here's what i'm getting: http://www.coolerguys.com/840556088417.html
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post #27 of 27 Old 01-24-2010, 05:49 PM
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Quote:
Originally Posted by Urlacher5454 View Post

I'm going to be getting a small fan to help with coloing and it has rubber feet on the bottom, I wonder if that will do the trick.

Here's what i'm getting: http://www.coolerguys.com/840556088417.html

Thanks for the link. That's a pretty cool web site/store.
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