Transformer stays warm when power off

[rumblestrip]

I picked up this minty little JVC RX-217 receiver this week. It looks practically like new inside and out and all the functions work as they should. So I thought I lucked out. After playing it for a couple of hours I turned it off. An hour or so later I came back to it only to notice that the transformer was still giving off heat! So I unplugged it, let it stand for half an hour, then came back to check on it again. No heat off the transformer now. Plugged it back in - power off still - and left it for a few minutes. When I came back, the transformer was giving off heat again. I’ve been collecting vintage audio for over 20 years now and never noticed this before in any other amp or receiver I’ve had. But not being technically savvy with it I have to wonder: Is this okay or is there something wrong with it. I hate to toss it without knowing for sure, but I don’t want to use it if it turns out to be a fire hazard. So what’s the story on this, please.

 

[petehall347]

sounds like the power switch is really a standby switch

 

[Shrugg]

I wouldn't worry about it. This should be normal behavior of this transformer. Since this receiver has a "soft" power off, which allows it to go into standby and power on from the remote, it still needs to draw power from the wall to keep the standby circuit energized. This would give off a little heat, especially if it is using the main transformer to drive the standby circuit (most receivers use a smaller standby transformer to save electricity, since it is a low power circuit.). As long as it is not too hot when off, it is ok to use.

 

[toxcrusadr]

There would still have to be some actual current usage in order to generate any heat, I would think. But perhaps there is some loss within the transformer even when little or no power is being used, so the only way to get it totally cold is to unplug it.

You can always unplug it or plug it into a power strip that has an on/off switch.

This phenomenon is actually responsible for a huge amount of power consumption in the household. Chargers left plugged in, standby mode on TVs and appliances, all kinds of stuff. Much of it is not really necessary. People who switch to solar or wind power spend a lot of time reducing the 'phantom load'.

 

[audiotemp]

The term used for this is "vampire power".

 

[woodj]

Wonder if the polarity of the plug is such that the hot side is running through and not toward the power switch. And then who knows?

Irelevant.

 

[SoCal Sam]

Vampire for the remote control and possibly channel presents. These do not draw much so warmth would be suspicious to me. How much heat is the transformer throwing off?

 

[audiotemp]

A transformer with its primary connected to the line and its secondary completely open still dissipates power. The main effect is "hysterisis loss" where magnetizing and de-magnetizing the core without drawing any power out still heats the core. Transformers vary in how much power they dissipate this way.

Power actually used by an amp or receiver while in standby is on top of that and may be more or less significant than the hysteresis loss. I have an integrated amp that dissipates 20W in standby because it leaves its pre-amp supplies powered at all times (there's no way to turn them off) and it generates those voltages from the main (and only) secondary windings. Most of the power it dissipates in standby happens in dropping resistors and voltage regulators. By today's standards it crazy but I think things were done this way for only a few years when remote controls were just coming into style. The Energy Star program was not begun until 1992...

 

[audiosignal]

or possibly the OP's unit could be defective as well. I have the JVC RX-715V (120WPC), which I think was made around the the time the RX-217 (40WPC) was, and my RX-715V **DOES NOT** emits any detectable heat (or hum) from outside, even with other gear stacked on top, when plugged in and turned off/stand-by. Metal case actually feels cold to the touch all around, top and bottom.

 

[MomirPeh]

or possibly the OP's unit could be defective as well. I have the JVC RX-715V (120WPC), which I think was made around the the time the RX-217 (40WPC) was, and my RX-715V **DOES NOT** emits any detectable heat (or hum) from outside, even with other gear stacked on top, when plugged in and turned off/stand-by. Metal case actually feels cold to the touch all around, top and bottom.

As far as I saw, your model of the receiver has a separate stand-by (much smaller) transformer, so you cannot compare these two in that respect.

 

[whoaru99]

Based on the schematic/service manual it appears the power transformer is energized all the time the unit is connected to the mains.

Because of that I believe the warmth is normal and there is absolutely nothing wrong with the receiver in this regard.

 

[rumblestrip]

Thanks, whoaru99, that's what I wanted to hear. As far as the 'standby mode' replies are concerned, it doesn't have one. There's no power button on the remote and the receiver doesn't turn on when you press one of the remote source buttons. You have to turn it on and off manually using the power button on the receiver. But thanks for the input, guys.