Hi. I made this project http://construyasuvideorockola.com/proyect_tda7294_mono.php (http://construyasuvideorockola.com/proyect_tda7294_mono.php) and here is the schematic and diagram (page 7 and 8) http://construyasuvideorockola.com/downloads/tda_90w_mono.pdf (http://construyasuvideorockola.com/downloads/tda_90w_mono.pdf)
I made the one with the split transformer, I dont know how you call the transformer with three outputs (center, negative,positive) Sorry for my English.
Heres how it went when I plugged it:
- The first thing was a pop like something exploded but it wasn't loud. I unplugged it immediately.
- There was a very subtle smell that something had burn when I reached to smell.
- I discharged the 4700uf caps. The one on the right did nothing, the one on the left, near the audio input, made a powerful discharge ( I made it with just a screwdriver, I know, I know...) Maybe you can see the blast on the picture.
And thats about it. Fuses are ok. Transformer is 28+28v, the voltage between the two opposite leads sums almost 60v. There is no trace of burnt or cracked material. The smell is gone.
So, I dont know where to start to debug this baby. Any help is appreciated.
Thanks
Ok I figured it out. I mixed the central tap with the positive or negative from the transformer. I can't believe I fall for that, Im so ashamed.
Anyway... Still not working. It makes a hum ( I dont know how many Hrz). I dont dare to poke around to feel if something is getting hot (maybe wrap mi finger with duct tape?) and dont know if its a god idea to leave it plugged while I test the circuit.
The audio signal gets to the input of the IC. Is it a good idea to test the output of the ic with my 2.1 pc speakers while its plugged?
thanks
When building power amplifiers the best thing you can do is get some 100 ohm 5W or 10W resistors and put them in series with the power supply to the power module. Put them between the big PSU caps and the power amp module, keeping any bypass caps on the power amp side in place. On rare occasions the resistors interfere with the operation of the amplifier and you have to drop the value 47ohm, 22ohm, 10 ohm.
It is useful sometimes to put a load on the amplifier using 10 ohm or 100ohm 5W or 10W resistors. No speakers.
With this set-up the resistors stop expensive parts blowing up. You can then probe the DC voltages around the amplifier and at the output to for checking and debugging purposes. A good thing to check is the voltage drop across the added resistors. This gives you the quiescent current. If the quiescent current is too high something is usually wrong. Once all checks out, and depending on your confidence you can then try smaller resistors say 10 ohm, then if all is good then remove the resistors and see how you go.
I *always* power-up new amplifier builds like this as it saves a lot of grief. It is also a standard configuration for debugging power amplifier problems.
Rob posted while I was typing, but I'll go ahead with what I was going to say:
You're probably going to get a lot of admonitions about safety. We don't want any of our forum friends to get hurt or killed. Please be very careful when the transformer is plugged into the mains voltage and watch out for the capacitors at all times. It's difficult to cover every possible safety issue and practice over the internet, so you're on your own unless you have an experienced person standing next to you.
Having said all of that, you may have damaged capacitors and/or diodes since something popped and you smelled an odor. If it were me, I'd carefully check those components. If those are ok, I'd check the voltages referenced on the schematic to make sure they are correct. I assume you have a voltmeter and you know how to use it safely.
If the voltages are correct, you might have blown the TDA chip.
That's about as far as I can take you. I'll let others take over from here.
Edit: It's also possible that a component could be connected in reverse, you've got a solder bridge, a bad solder joint, or a broken trace. Check for those too.
Quote from: Rob Strand on October 20, 2016, 03:45:19 AM
When building power amplifiers the best thing you can do is get some 100 ohm 5W or 10W resistors and put them in series with the power supply to the power module. Put them between the big PSU caps and the power amp module, keeping any bypass caps on the power amp side in place. On rare occasions the resistors interfere with the operation of the amplifier and you have to drop the value 47ohm, 22ohm, 10 ohm.
It is useful sometimes to put a load on the amplifier using 10 ohm or 100ohm 5W or 10W resistors. No speakers.
With this set-up the resistors stop expensive parts blowing up. You can then probe the DC voltages around the amplifier and at the output to for checking and debugging purposes. A good thing to check is the voltage drop across the added resistors. This gives you the quiescent current. If the quiescent current is too high something is usually wrong. Once all checks out, and depending on your confidence you can then try smaller resistors say 10 ohm, then if all is good then remove the resistors and see how you go.
I *always* power-up new amplifier builds like this as it saves a lot of grief. It is also a standard configuration for debugging power amplifier problems.
Thank you very much.
I didn't get where the 100hom resistor goes.
I did understand what you said about replacing the speaker with a resistor.
(https://c2.staticflickr.com/6/5725/29813608424_e5aa444479_b.jpg)
(https://c2.staticflickr.com/6/5635/30358217661_1b13fa275e_b.jpg)
(https://c2.staticflickr.com/6/5537/29813612024_b5dfe9ec29_b.jpg)
I already fixed the polarity from the transformer.
Quote from: Jdansti on October 20, 2016, 03:55:32 AM
Rob posted while I was typing, but I'll go ahead with what I was going to say:
You're probably going to get a lot of admonitions about safety. We don't want any of our forum friends to get hurt or killed. Please be very careful when the transformer is plugged into the mains voltage and watch out for the capacitors at all times. It's difficult to cover every possible safety issue and practice over the internet, so you're on your own unless you have an experienced person standing next to you.
Having said all of that, you may have damaged capacitors and/or diodes since something popped and you smelled an odor. If it were me, I'd carefully check those components. If those are ok, I'd check the voltages referenced on the schematic to make sure they are correct. I assume you have a voltmeter and you know how to use it safely.
If the voltages are correct, you might have blown the TDA chip.
That's about as far as I can take you. I'll let others take over from here.
Edit: It's also possible that a component could be connected in reverse, you've got a solder bridge, a bad solder joint, or a broken trace. Check for those too.
I hope its the bridge. Ill check that. Caps seems fine and ill be damn if the tda blew.
Thanks for worrying.
Checkout this pic,
http://3.bp.blogspot.com/_9qUcTZUGHXA/Sp11PgadWRI/AAAAAAAAAQs/4R7_NY5k7SY/s250-c/audio-amplifier-50W.gif
The resistors that go in series with the power can be placed where the fuses are. I see fuses in your pics. Remove the fuses and solder the resistors on the back of the fuse holders. (For this job, I actually have some blown fuses which have resistors soldered to the fuses so I can just plug them into the fuse holders.)
Quote from: guidoilieff on October 20, 2016, 04:42:42 AM
I didn't get where the 100hom resistor goes.
in spanish
100ohm en serie con la fuente de poder, como un fusible, limitan el corriente que puedan dañar los copomentes
Quote from: guidoilieff on October 20, 2016, 04:42:42 AM
I did understand what you said about replacing the speaker with a resistor.
no uses parlantes, reemplaza las por resistencias de potencia, es mucho mejor para hacer mediciones.
ya que la carga electricas es constante, no komo en un parlante donde la resistencia varia con la frecuencia.
y evitas el constante sonido de un tono de testeo.
short in english
why 100ohm and why load resistor in place of speakers,
...sorry
I built an amp with this chip from a schematic by elect*r and it works well. I remember that they wrote that the specs of this chip were a bit optimistic in their eyes and they therefore had limited the output to 60 watts, just to be on the safe side. If you can't figure this out, I can try to find the schematic, but I'll have to search for it, so this might take some time...
In the picture the TDA is burn, before you plug the transformer you need to check if have the correct voktaje, i see you from argentina so the electrical source is 220vac, and say Reductor to 150vac check before, if you need to talk on spanish just send a private :) and we talk . I use many TDA's to get sound and amps , are good ones to do and more wasy like TDA1562, tda1557q, tda8560q
Quote from: maartendh on October 22, 2016, 05:46:41 PM
I built an amp with this chip from a schematic by elect*r and it works well. I remember that they wrote that the specs of this chip were a bit optimistic in their eyes and they therefore had limited the output to 60 watts, just to be on the safe side. If you can't figure this out, I can try to find the schematic, but I'll have to search for it, so this might take some time...
Cool, thats the name of the user on this forum? I can look for it if you're too busy. If you find it it would be great!
Quote from: Vitrolin on October 21, 2016, 04:54:15 PM
Quote from: guidoilieff on October 20, 2016, 04:42:42 AM
I didn't get where the 100hom resistor goes.
in spanish
100ohm en serie con la fuente de poder, como un fusible, limitan el corriente que puedan dañar los copomentes
Quote from: guidoilieff on October 20, 2016, 04:42:42 AM
I did understand what you said about replacing the speaker with a resistor.
no uses parlantes, reemplaza las por resistencias de potencia, es mucho mejor para hacer mediciones.
ya que la carga electricas es constante, no komo en un parlante donde la resistencia varia con la frecuencia.
y evitas el constante sonido de un tono de testeo.
short in english
why 100ohm and why load resistor in place of speakers,
...sorry
Got it, thanks!
Anyway, I have no idea which readings I should do. There are so few components... My guess is that in just a fraction of a second when I switched on and off the amp with the reversed polarity the ic burnt that easy.
shouldn't diodes prevent that?
Quote from: Rob Strand on October 20, 2016, 03:45:19 AM
When building power amplifiers the best thing you can do is get some 100 ohm 5W or 10W resistors and put them in series with the power supply to the power module. Put them between the big PSU caps and the power amp module, keeping any bypass caps on the power amp side in place. On rare occasions the resistors interfere with the operation of the amplifier and you have to drop the value 47ohm, 22ohm, 10 ohm.
It is useful sometimes to put a load on the amplifier using 10 ohm or 100ohm 5W or 10W resistors. No speakers.
With this set-up the resistors stop expensive parts blowing up. You can then probe the DC voltages around the amplifier and at the output to for checking and debugging purposes. A good thing to check is the voltage drop across the added resistors. This gives you the quiescent current. If the quiescent current is too high something is usually wrong. Once all checks out, and depending on your confidence you can then try smaller resistors say 10 ohm, then if all is good then remove the resistors and see how you go.
I *always* power-up new amplifier builds like this as it saves a lot of grief. It is also a standard configuration for debugging power amplifier problems.
I tested it that way. I think the resistors are 2W because the local electronic store lady seemed a bit confused about watts ratings. All are 100ohm 5%
In the negative rail where the fuse was It read 37 volts, and in the positive the same. The "negative" resistor got hot but the "positive resistor" didn't.
When removing each resistor for each reading, the negative had a 0,47amps reading and the positive none.
When its unplugged the positive rail holds the voltage (that includes pin 7 (+vs) and pin 13 (+vcc)) while the negative rail quickly fades out.
Also, the load resistor got hot.
Does it makes sense?
Elect*r is the name of a magazine, they get nasty when you copy their work. I had a look at the schematic in my files, it is not different from the application in the datasheet, I think, only they limited the supply to + and - 30 volts. Mute and standby are not connected to switches, but permanently connected to positive supply.
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