??? Need some transformer help!!!

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EFraelich82

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Let's just get this out of the way... I have a basic concept of electrical principles however it would be generous to even call me a beginner. I have a powered subwoofer for my home stereo system that is broken and needs to be fixed. Although I guess it is not very common for a transformer to go bad, I really think mine has.

So here is the story so far. I plug plug the subwoofer in and nothing. No power light, nothing. I check the power at my outlet with a standard 120V test light and it is fine. It has power. I take the speaker out and hook it directly up to an amp that I know works and it is fine. Put the speaker back in. I take the electronic board out and find 2(two) 250V 4amp fuses on the board. One of them is blown. WOOOHOOOOO I found my problem. I go to Radio Shack and buy new fuses. Put them in and still nothing. Double checked the fuses and they are both good. From looking at the back of the board I can see that the leads coming into the board from the transformer go directly to these fuses so obviously this is the current's first stop into the board (from the transformer).

The board doesn't show any signs of burning or bad connections so I think the fuse saved the day as it was designed to do. That being said, I don't think the board is the problem. If the fuse on the board was blown, I'm guessing that means the transformer was throwing it too much current.

Let me just preface my next diagnostic stroke of genius by telling you up front that I didn't even know what the transformer was called until I did a google search so bear with me! So I have the transformer completely seperated from the board now and on my coffee table. It has a 2 wire lead coming into one side directly from the standard 120V plug for the wall. The other side has 3 wires, 2 blue and an orange wire. From looking at the back of the board where the fuses are located I can tell that the 2 blue wires are one side of the lead that are only seperated to incorporate a break for the fuses. The other orange wire goes straight past the fuses into the board. So my stroke of genius is: I then take a short piece of speaker wire and connect the blue wires to each end of the speaker wires. Then I twist the free end of the speaker wires together to complete the circuit of the blue wires (like the fuse would do on the board). I take my Radio Shack battery tester and hook one end to the end of the orange wire and the other end to my speaker wire representing the blue wires. Then I plug the transformer into the wall VIA the 2 wires on the opposite side coming directly from the wall plug.

Again, I am not very smart with any of this but since my highest setting on my battery tester is 15 volts, I would think that 250 volts would at least make the needle twitch a LITTLE, if not just destroy my battery tester (small price to pay). I tested the lead going into the transformer from the wall where I spliced my cord with a standard 120V test light and it has power so I know it isn't my power cord or my outlet. The transformer is definately getting power on one end... it just seems like nothing is coming out the other end.

I know that diagnostic test probably should have killed me or at best ruined a perfectly good battery tester but is still seems like it has to be the transformer for me not to even get a twitch on the needle of the battery tester.

Finish laughing at me and with banter aside, please tell me what you think.
 

EFraelich82

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Maybe I can kill 2 birds with one stone... if I am right and you think the transformer is the problem... how the crap do I find a replacement and how do I figure out which one I would need? I think it is a step up transformer (going from 120 volts to 250) and I THINK it would be 4 amps since the board has two 4 amp fuses (or would it be doubled to 8amps?) but after that, I have no idea. This doesn't seem to have a part number or anything on it however this is what is stamped on the top:

TTI112001-0120
TTI1120Ic012
Built in thermal fuse
fitted D130 Degrees Celsius
TP76U57F TEN PAO

Any help you can offer would be GREATLY appreciated.
 

Jadnashua

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Google a transformer. Hotwiring this could have burned up things. It sounds like the subwoofer system has it's own amplifier. A transformer changes the voltage, or isolates the input from the output. A power supply like this would likely use a step-down transformer - that means that it would change the incoming 120vac to something maybe around 20-30 vac. It would then go to a rectifier, which is the first step towards changing the a/c to dc, which is needed to power the amplifier. An overload could be from something in the rectifier section. It is possible, but rare that a transformer dies. It is more likely some semi-conductor item in the rectifier/regulator section. Bypassing the fuse is a good way to blow the rest of the board up.

Many of today's power supplies are switching supplies. These use an oscillator to feed a transformer at high frequency, which makes it more efficient to produce dc and uses smaller circuits (smaller devices can be used at higher frequencies).

If the primary of the transformer has power, you should measure a/c across the secondary. how much would depend on the winding ratio. The third wire could be for an additional output if the power supply requires multiple voltages. the fuses are normally on the input to the transformer, not the output. With power off, and the line disconnected, you can get an idea if the transformer is open or shorted out by checking resistance across the primary, and then across the secondary. There should not be any continuity from primary to secondary. These values will be low and the secondary will normally have less than the primary (in a step-down). The inductance will go up when actual current is flowing caused by the magnetic fields interact with the core. the math to figure out what those values are can get complex. Unless you luck out and can isolate a cooked component, you're unlikely to repair this yourself, especially if it uses a switching power supply (which most modern stuff does). A transformer failure mode is to either open up one of the windings (rare), or a breakdown of the insulation so that it shorts out (also rare).
 

EFraelich82

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Yes the subwoofer does have it's own built in amplifier. I did google how to diagnose a transformer however it is greek to me. I don't even think I have the tools to measure resistance. I didn't short out the fuses, they are located on the amplifier circuit board. I know a lot about computers so I know better than to put any type of inappropriate power source to a circuit board. I think the cooked component is the transformer. I guess a better way to word my question would have been this: If a transformer of this type is working properly, when I plug it into the wall and put a battery tested on the other end of the leads, wouldn't I get some action on the needle?
 

Nukeman

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It is not likely a problem in the transformer. A transformer is essentially just some coiled up wires. It would take something unusual to kill it. I think the issue that you are having is that you are using a battery tester (made for DC voltage) to check the transformer (AC voltage). Depending on how the battery tester is made, it is likely setup to block any AC voltage coming in and that is why you are not seeing anything. Your best bet is to hit RadioShack, an autoparts store, or similar and pickup a cheap DMM (digital multimeter). They can be had for a little as $10-$20 or so. You just need something basic (AC volts, DC volts, and resistance (Ohms)).

As Jim mentioned, the output from the transformer might be 30 VAC or so (might be more and might be less). For the fuses, the 250V rating really doesn't mean anything except that you shouldn't use these fuses if the voltage is higher than that. The important thing is the current rating (4 amps).

It sounds like the signal is being passed through to the speaker, but is not being amplified. You might have a dead transistor in the amplifier circuit or there may be some other part of the power supply circuit that is dead. Checking the board may be difficult as you have to figure out what each part does and what volatge/behavior it should see. Often related items will be grouped together (power supply section, filtering section, amplifying section, etc.), but that is not always the case. There also may be additional circuits that are in there that are not really needed, be they add them to please the consumer (eliminate turn-on "thump", equilizer/filter, additional volume control, etc.).

If you have some electronics background, you could trace or the circuits, draw up a schematic, figure out what each thing does, then start testing. Without that, you could only do some basic tests and look for visable damage and hope to get lucky.
 

Jimbo

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You are confusing the issue with talk of "phases" because we are talking about single phase power. The current flowing in any wire in the circuit is the same at any moment in time. Measured voltages are explained by Kirchoff's law.

It is true that if you create a reference point such as the center tap of a transformer, THEN at any moment in time, the voltage at the two "hot" wires will be 180º out of phase with each other MEASURED WITH RESPECT TO THAT CENTER REFERENCE.

Anyway, it is a single phase circuit. If 20 amps is flowing, the same 20 amp is flowing through any wire in the circuit which you would measure. Assuming this is somehow driving speakers, then the load is not pure resistive but for this discussion, we will not need to bother with the phasing of current vs. voltage. It is not applicable to the discussion.
 

EFraelich82

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Thanks!

It is not likely a problem in the transformer. A transformer is essentially just some coiled up wires. It would take something unusual to kill it. I think the issue that you are having is that you are using a battery tester (made for DC voltage) to check the transformer (AC voltage). Depending on how the battery tester is made, it is likely setup to block any AC voltage coming in and that is why you are not seeing anything. Your best bet is to hit RadioShack, an autoparts store, or similar and pickup a cheap DMM (digital multimeter). They can be had for a little as $10-$20 or so. You just need something basic (AC volts, DC volts, and resistance (Ohms)).

As Jim mentioned, the output from the transformer might be 30 VAC or so (might be more and might be less). For the fuses, the 250V rating really doesn't mean anything except that you shouldn't use these fuses if the voltage is higher than that. The important thing is the current rating (4 amps).

It sounds like the signal is being passed through to the speaker, but is not being amplified. You might have a dead transistor in the amplifier circuit or there may be some other part of the power supply circuit that is dead. Checking the board may be difficult as you have to figure out what each part does and what volatge/behavior it should see. Often related items will be grouped together (power supply section, filtering section, amplifying section, etc.), but that is not always the case. There also may be additional circuits that are in there that are not really needed, be they add them to please the consumer (eliminate turn-on "thump", equilizer/filter, additional volume control, etc.).

If you have some electronics background, you could trace or the circuits, draw up a schematic, figure out what each thing does, then start testing. Without that, you could only do some basic tests and look for visable damage and hope to get lucky.

That is the most helpful response so far. I appreciate everyone's help. No i don't think the speaker is getting any signal at all from the board. I only know the speaker works because I removed the driver completely and tested it directly to my receiver and it works normally. I would tend to agree with you that a solid state part like a transformer shouldn't fail very often. There is an LED light on the front of the sub that comes directly off the board to show when the unit has power. That is not coming on either so I am pretty sure I have an issue with the power supply. The board COULD still be messed up or something since the amp is not working however since my power light is dead too, I'm thinking I for sure have an issue with power. The fuses are the gateway to the circuit board power and since I started with a blown fuse, I think that could be an indication of a failure in front of the fuses, at the gateway of the circuit board. Literally the only component in front of the fuses is the transformer. next it is the power cord coming into unit from the wall plug so there is no other power supply component that it could be. I need to test it out properly to diagnose or rule that out for sure though. I'm going to take your advice and buy a multimeter tonight and try testing it the correct way. I'll post whatever my results are just in case anyone is curious
Thanks again!!!
 

Jadnashua

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Something electronic in the board is trying to draw too much current, which blows the fuses. The transformer in and of itself is not a solid-state device - it is all wires and metal and insulation. To qualify for a solid-state device, it needs to have some transistors, diodes, chips, scrs, etc. in it. With nothing connected to the secondary (the output) of a transformer, you could have line voltage across the primary, and because there would be little induced current being drawn with the open secondary, there would be very little power drawn. There is only some significant power drawn when the secondary is connected to something and supplying current to it unless the primary winding developed a short internally (not common and you'd notice a characteristic smell of burnt electronics).

The transformer is likely there for the power supply to allow the amplifier to work. It outputs lower ac voltage than line. It then needs to go into a rectifier circuit to transform it into a dc value. This will usually have a regulator circuit in it to make the voltage stable and smooth it out so there's no ripple (unevenness in the dc voltage level). Then, the amplifier circuit itself would take the signal from your amp and feed the sub-woofer. Since the sub-woofer doesn't like to try to reproduce higher frequency inputs, it may have a filter circuit to restrict the signals that go to the amplifier. It may also have a shaping circuit (equalizer) to compensate for the woofer frequency response.

Depending on the sophistication, this circuit can be quite complex. If the power supply is a switching type, even that now adds additional circuitry. WIthout a schematic and some test tools and the knowledge to go along with it, your best chance of fixing it is to identify something that is cooked, and replace it. That may not be all of the problem since it may have blown because something else down the line died and tried to make it draw more current or allowed higher voltages to get to it which killed it.

So, your best bet is to send it in for repair. Sometimes, it is cheaper to just replace the board (assuming you can get it). Skilled diagnostisians command good wages, so the cost benefit of repair verses replace is often moved to replace.
 

whitney0125

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I agree about jadnashua said. The best thing that you can do is to bring your speakers to the electrician so he will be the one to check for every wirings..

______________
diesel generator/s
 

Mikey

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I'm betting the two blue wires feed a full-wave bridge rectifier curcuit (the orange wire is the center-tap), and something in the DC power section fried and blue the fuse on one side of the input AC -- maybe a diode somewhere. As nukeman pointed out, a cheap mulitmeter will get you a long way down the road to diagnosing the problem, but for best results you need a schematic diagram of the device, and someone who knows how to read it and use the meter. Just FMI, what make & model is the subwoofer, and how old is it?
 

EFraelich82

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I'm betting the two blue wires feed a full-wave bridge rectifier curcuit (the orange wire is the center-tap), and something in the DC power section fried and blue the fuse on one side of the input AC -- maybe a diode somewhere. As nukeman pointed out, a cheap mulitmeter will get you a long way down the road to diagnosing the problem, but for best results you need a schematic diagram of the device, and someone who knows how to read it and use the meter. Just FMI, what make & model is the subwoofer, and how old is it?

Thanks! I bought a decent, auto ranging multimeter and attempted to test it however could not get any voltage from any of the contact points (except the live feed coming from the wall). The subwoofer is an Onkyo SKW-150. It is about 5 years old however I think they still make them for other current systems.
 

Mikey

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The service manual, with a schematic diagram, is available as a download at several sites on the Web - just Google "Onkyo SKW-150 schematic". Unfortunately, they usually cost a few bucks, but with the manual, the meter, and basic electronics knowledge you can probably narrow it down to a replaceable component (or components). If you've replaced the fuse, and still see no voltage (AC) across the 2 blue wires, the odds are the transformer is fried. With the service manual in hand you can find either a part number for it, or values for the voltage & current ratings for it, so you could buy a replacement. You should also check downstream of the transformer to see WHY it fried...
 

EFraelich82

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The service manual, with a schematic diagram, is available as a download at several sites on the Web - just Google "Onkyo SKW-150 schematic". Unfortunately, they usually cost a few bucks, but with the manual, the meter, and basic electronics knowledge you can probably narrow it down to a replaceable component (or components). If you've replaced the fuse, and still see no voltage (AC) across the 2 blue wires, the odds are the transformer is fried. With the service manual in hand you can find either a part number for it, or values for the voltage & current ratings for it, so you could buy a replacement. You should also check downstream of the transformer to see WHY it fried...

nice, thanks!!!
 

Nukeman

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Although the transformer should show a voltage unloaded, try to add a load just for kicks and test again. Get a couple 10k resistors (1/4W or 1/2W is fine). Put one resistor between 1 blue wire and the orange and put another between the other blue wire and the orange wire. Power it up and measure the voltage (on AC volts) across each resistor and see what you get.

If you still get nothing, then the transformer is toast. Then it is just a matter of figuring out if the transformer fried 1st and caused the blown fuse, etc. or if there is something down the line that failed and caused the blown fuse and dead transformer.
 

hj

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A good transformer would show voltage without anything connected to it. If it has lost its capacity, then connecting a load to it could drain whatever power it can produce and THAT would show no voltage, not the other way around. Just do not do like a friend of mine did one time and plug the speaker into a 115 v. outlet. The sound is incredible, and so is the shattered speaker cone.
 

Nukeman

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True, if it is just a basic transformer. However, there are different types of transformers and we don't know for sure what type this one is. In addition, this transformer may have additional features such as thermal protection, etc.

Here is a basic article on transformer testing: http://ezinearticles.com/?Testing-a-Transformer---How-To-Accurately-Test-A-Transformer&id=56803 A Google search will bring up a bunch of other ones that may help you too.

Doing the test that I mentioned would cost $.50 and take 2 minutes. If you still get nothing, you could test the resistance on the windings to see if you have an open winding. Either an open winding or a shorted winding could be the cause the lack of voltage on the secondary side.
 
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herrry.james

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DO you have three wires going into the 120 side black white and ground two coming out black white or red white only one way to wire it up where did you buy the trans.from a supply house or from some body.What did the papers that come with it say.Probably a bad trans.Take it back or buy a new one.
 
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