Someone help about transformator

Audioguru

Joined Dec 20, 2007
11,251
15 watt rms per channel = 30 watts X 2.84 = 85.2 watts peak to peak power. Awesome!:D
SG
85.2 Whats of peak to peak power at low distortion is 170.4 Whats when it is clipping and distorting like crazy. The power is even more (music power) when the sound is only for a moment before the power supply voltage sags. Maybe 200W.
 

Tonyr1084

Joined Sep 24, 2015
4,037
Late entry into this conversation. Did I read you first said there was no lights on at all, then later say there was some lights? From what I'm reading everyone is giving you some pretty clear advice as to what to look for. Mixed in with it is some pretty savvy info on wattages and outputs. I really can't add anything to that.

Here's the reason why I'm even getting into this conversation: First, and admittedly, it seems like you're not measuring the transformer correctly. I "SUSPECT" you've made some fundamental error. As you've been told, it's rare for a transformer to go open. Let alone both primary and secondary WITH center tap. If your transformer truly is open as you say it is then you should put the stereo away and start playing lotto. With odds like that you are guaranteed to win the lottery. Sorry if I come off like a jerk - I don't mean to down play your knowledge and/or ability to trouble shoot your stereo. When it comes to outputs and ratings, it's common for a stereo manufacturer to highlight the wattage as a "MAX". That's different from a sustained wattage. Also, you may have a left channel with a MAX of 40 watts as well as the right channel. They will tell you it's 80 watts because they can. I've seen that done for many years now, and way back in the early 70's I sold stereo equipment that was rated exactly this way.

The second thing I want to say is something that is going to make you think I believe you're unintelligent. No - I don't think that at all. However, let me ask this obviously dumb question: The outlet you plug the stereo into - - - is it working properly? I had a friend change a timing belt because his car wouldn't start. The FIRST thing I asked him was "Is there gas in the tank?" A dumb look came over his face, he checked the gas gauge and said "I guess not." The point is that sometimes we overlook the most obvious answers to life's questions.

A third thing I wanted to share is this: I repaired my stereo. It blew the fuse. 7 amp. When I disconnected the transformer from the circuit the fuse would not blow. So I knew it was something after that. After tracing things out I discovered my bridge rectifier had shorted. One of the four rectifiers failed. That blew the fuse. Not the transformer. When I replaced the rectifier the stereo works. And I didn't replace it with one of the same ratings I went up about 50% higher rated than the original. There's no harm in putting something in a circuit that is MORE capable than the original equipment.

These things, the idea you're measuring incorrectly, the failure mode along with your statements of lights and no lights, along with the understanding that transformers seldom fail, let alone the idea that the primary, secondary AND center tap ALL show open would make for circumstances that are so unlikely to happen that I don't think anyone here is going to believe the transformer has failed in such fashion. IF something went wrong in the circuitry that had the ability to smoke the transformer then it's very likely you have a slew of other failures in your circuitry. IF the transformer is completely open then there is no possibility of ANY lights lighting up. Hence, my confusion at your comments. Unless I mis-read something, which I'm known to do.

Start over. Square 1. Do you have primary voltage? Be careful measuring please. If you have primary voltage (a.k.a Line voltage) then do you have secondary voltage? Secondary voltage over the entire transformer secondary or half voltage from end to center tap? Both ways? Are you testing this with the rest of the stereo electronics disconnected? if not - disconnect all things. As much as possible. Some stereo equipment is modular and a transformer may be attached to a board along with its diodes and filter caps. If you're measuring the coil windings via an output terminal on a board then it's possible you're trying to measure through a blown diode or other open circuit. Frankly I find it impossible to believe the transformer is in TOTAL failure (primary and secondary). That just doesn't happen. But like I said, if something has blown the transformer then whatever it was has also likely killed just about everything else on the stereo.

Again, I'm not trying to be a jerk. If I come off that way - my sincere apologies.
 

sghioto

Joined Dec 31, 2017
1,038
as you can see it's a digital one and it can measure under 1 ohm
So is the transformer primary open or not?
Is the secondary open or not?
It is possible for both to open but usually it's only the primary.
The internal fuse inside a lot of transformers consisted of a short wire, about .5 inch. or so, of a much smaller gauge wire connected between one end of a primary winding and lead wire coming out. This was normally found under a few layers of the material wrapped around the windings. I know this from over 25 years in consumer electronics repair.
If this is the case replacing that "fuse" does not guarantee it will work. Many times there is a short in the internal windings that cause the fuse to pop.
SG
 
Last edited:

MisterBill2

Joined Jan 23, 2018
4,897
View attachment 171325 as you can see it's a digital one and it can mesure under 1 ohm
View attachment 171325 as you can see it's a digital one and it can mesure under 1 ohm
OK, I was totally unsure about what type of ohm meter you were using. That meter will be telling the truth, certainly.
Some analog meters will certainly give a wrong impression, that was my concern.
Now as I look at the photos in post#26 I see some solder connections that cause some concern . It is not at all clear what they are for, and they look to connect to more than one circuit. What can you say about them?
 

MisterBill2

Joined Jan 23, 2018
4,897
The only time that I had a transformer with all of the windings open it was the result of a direct lightning hit, and also the face of that clock radio was blown off. So it does happen, but not frequently. Also, if it was a direct lightning hit that damaged the amplifier there may be other problems as well.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
154
Late entry into this conversation. Did I read you first said there was no lights on at all, then later say there was some lights? From what I'm reading everyone is giving you some pretty clear advice as to what to look for. Mixed in with it is some pretty savvy info on wattages and outputs. I really can't add anything to that.

Here's the reason why I'm even getting into this conversation: First, and admittedly, it seems like you're not measuring the transformer correctly. I "SUSPECT" you've made some fundamental error. As you've been told, it's rare for a transformer to go open. Let alone both primary and secondary WITH center tap. If your transformer truly is open as you say it is then you should put the stereo away and start playing lotto. With odds like that you are guaranteed to win the lottery. Sorry if I come off like a jerk - I don't mean to down play your knowledge and/or ability to trouble shoot your stereo. When it comes to outputs and ratings, it's common for a stereo manufacturer to highlight the wattage as a "MAX". That's different from a sustained wattage. Also, you may have a left channel with a MAX of 40 watts as well as the right channel. They will tell you it's 80 watts because they can. I've seen that done for many years now, and way back in the early 70's I sold stereo equipment that was rated exactly this way.

The second thing I want to say is something that is going to make you think I believe you're unintelligent. No - I don't think that at all. However, let me ask this obviously dumb question: The outlet you plug the stereo into - - - is it working properly? I had a friend change a timing belt because his car wouldn't start. The FIRST thing I asked him was "Is there gas in the tank?" A dumb look came over his face, he checked the gas gauge and said "I guess not." The point is that sometimes we overlook the most obvious answers to life's questions.

A third thing I wanted to share is this: I repaired my stereo. It blew the fuse. 7 amp. When I disconnected the transformer from the circuit the fuse would not blow. So I knew it was something after that. After tracing things out I discovered my bridge rectifier had shorted. One of the four rectifiers failed. That blew the fuse. Not the transformer. When I replaced the rectifier the stereo works. And I didn't replace it with one of the same ratings I went up about 50% higher rated than the original. There's no harm in putting something in a circuit that is MORE capable than the original equipment.

These things, the idea you're measuring incorrectly, the failure mode along with your statements of lights and no lights, along with the understanding that transformers seldom fail, let alone the idea that the primary, secondary AND center tap ALL show open would make for circumstances that are so unlikely to happen that I don't think anyone here is going to believe the transformer has failed in such fashion. IF something went wrong in the circuitry that had the ability to smoke the transformer then it's very likely you have a slew of other failures in your circuitry. IF the transformer is completely open then there is no possibility of ANY lights lighting up. Hence, my confusion at your comments. Unless I mis-read something, which I'm known to do.

Start over. Square 1. Do you have primary voltage? Be careful measuring please. If you have primary voltage (a.k.a Line voltage) then do you have secondary voltage? Secondary voltage over the entire transformer secondary or half voltage from end to center tap? Both ways? Are you testing this with the rest of the stereo electronics disconnected? if not - disconnect all things. As much as possible. Some stereo equipment is modular and a transformer may be attached to a board along with its diodes and filter caps. If you're measuring the coil windings via an output terminal on a board then it's possible you're trying to measure through a blown diode or other open circuit. Frankly I find it impossible to believe the transformer is in TOTAL failure (primary and secondary). That just doesn't happen. But like I said, if something has blown the transformer then whatever it was has also likely killed just about everything else on the stereo.

Again, I'm not trying to be a jerk. If I come off that way - my sincere apologies.
i understand what you are trying to say and today i checked the secondary windings and the centar taped one showed 1.5 ohms and the other one showed 4 ohms and the something strange is happening with it when i move the wire up it is mesuring 40 ohms and when i move the wire down is open end i taped the wire up and put a 40 watt bulb in series with the primary winding and pluged it into mains ofcourse removed from the circuit and the lightbulb was lit very slightly and when i mesured the secondary it was mesuring 7.5 volts on the center tap which is 15 volts both together and on the other secondary winding it was mesuring 5volts and that was strange beacose both voltages were too small for the amplifier and the other circuitry any advice.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
154
OK, I was totally unsure about what type of ohm meter you were using. That meter will be telling the truth, certainly.
Some analog meters will certainly give a wrong impression, that was my concern.
Now as I look at the photos in post#26 I see some solder connections that cause some concern . It is not at all clear what they are for, and they look to connect to more than one circuit. What can you say about them?
I think you are thinking about those two black wires those are ground for the speaker output connector that is on the back site of the system.Is that what you see or is it something different be more specific
 

Thread Starter

Dzoro

Joined Feb 1, 2019
154
i can't open it
Oh i know that circuit from the end when i first opend the system and saw the stk chip i googled it and i was tryng to see if the conections were like that on the circuit and those were exactly like that but it has some smal bjt transistors which i don,t know what they are for
 

Wendy

Joined Mar 24, 2008
21,930
My first thought (and it might be a brain fart) is it possible there are capacitors inline on both sides?
 

Thread Starter

Dzoro

Joined Feb 1, 2019
154
And today also i removed the amplifier board,hook speakers to it,hook input to it and powered it with +-9 volts ac that is the maximum voltage centartaped transformer that i have and that is around 22 vdc as i mesured and nothing hapend do anyone know what is the minimum voltage rating for the chip or is not working beacose the chip is burnt.And last question do anyone knows how to check if the chip is bad.
 

Tonyr1084

Joined Sep 24, 2015
4,037
i understand what you are trying to say and today i checked the secondary windings and the centar taped one showed 1.5 ohms and the other one showed 4 ohms and the something strange is happening with it when i move the wire up it is mesuring 40 ohms and when i move the wire down is open end i taped the wire up and put a 40 watt bulb in series with the primary winding and pluged it into mains ofcourse removed from the circuit and the lightbulb was lit very slightly and when i mesured the secondary it was mesuring 7.5 volts on the center tap which is 15 volts both together and on the other secondary winding it was mesuring 5volts and that was strange beacose both voltages were too small for the amplifier and the other circuitry any advice.
OK, that was a bit of a long run-on sentence. Lets see if I understand: You say you connected a 40 watt bulb in series with the transformer, and the bulb lit; albeit dimly. Then the primary is not open. If it were open then the bulb would not light. You also state you get 15 volts across the three wire section of the transformer (the part with the center tap). Yes, that's probably below what it should be. From what I've picked up in the conversations you should see 21 volts from center to either side. Turns out that when you multiply 15 volts (AC) by 1.414 you get 21 volts peak. When rectified and filtered you should see 21 volts from center tap to either of the other two legs of the secondary.

Having gone back and examined the photos you've posted, it looks like there's two secondary coils. The two black wires on the right side as viewed in the photograph would be isolated from the other three wires to the left. So - the three wires on the left appear to be what drives the amplifier (as others have already said) The red wire in-between the two black wires is the center tap. From either black wire (on the left) to the red wire you should see 15 VAC (RMS) (Fancy term for the average useful voltage from an AC sine wave). From black to black you should see 30 VAC (RMS) (Root Mean Squared). In short hand terms, multiply the RMS voltage by 1.414 to get the peak voltage, the voltage you'll see when rectified and filtered. None of that matters. What matters is that your transformer appears to be doing something. If you're measuring 15 volts across the two left black wires then something is probably wrong with the transformer. The secondary can be shorted internally, which would explain both the low voltage AND the high draw to the primary which likely blows the fuse. At this point I'd expect (or hope) that nothing else in the circuitry has been harmed.

So your issue is from where to get such a transformer. Those two black wires on the right - - - what voltage did you get from those? Oh, and I hope these voltage readings on the secondaries was not done with the lightbulb in series with the primary. If so - hard wire the transformer directly to mains and read and report all voltages. For future reference it may help if you label each wire with a number or a letter. Let A & B be the primary side; C, D & E the three wires of the secondary with the center tap, D being the tap; and F & G for the last two wires on the right. By arbitrarily assigning designations to the leads of the transformer we can ask you to perform specific checks on specific wires and have you report your findings.

The idea that when you wiggle the wire you get changing readings may be of some concern, or it may be a weak connection. Could be the wire itself touching the probes of the meter. Please don't do that with the primary side while powered - you'll get an unpleasant shock and likely to holler out my name for not warning you. Of course I think you're smart enough not to touch the primary side while powered.

If the transformer turns out to be good then the next thing to check would be the diodes. Each one should be checked outside of the circuitry. Otherwise you could get false readings difficult to interpret, and reporting errors in that condition can mislead us to diagnosing things incorrectly.

Best of luck.
 

sghioto

Joined Dec 31, 2017
1,038
do anyone know what is the minimum voltage rating for the chip or is not working beacose the chip is burnt.And last question do anyone knows how to check if the chip is bad.
No specs on the minimum voltage. Recommended is + and - 21 volts. When a chip is burnt it's BAD.
SG
 
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