Hi,
The problem changed. The old tests are not valid. The multimeter was somehow limiting the current going to the amp.
I've removed the multimeter from the circuit, installed a ampmeter and tryed to turn on the amp directly on the power supply, this time with a 10A fuse.
The amp starts pushing out the power supply maximum current (20A) and the fuse blows almost instantly.
Should i start to think in any output transistor is shorted out? Any tips?
The problem changed. The old tests are not valid. The multimeter was somehow limiting the current going to the amp.
I've removed the multimeter from the circuit, installed a ampmeter and tryed to turn on the amp directly on the power supply, this time with a 10A fuse.
The amp starts pushing out the power supply maximum current (20A) and the fuse blows almost instantly.
Should i start to think in any output transistor is shorted out? Any tips?
Go back to the current liming setup that you had before and measure the DC voltage across each of the emitter resistors connected to the output transistors. Do all read approximately 0.001v?
Does any one or any group read significantly higher than the rest?
Does any one or any group read significantly higher than the rest?
Hi,
The heavy resistance i put in series (to reduce the current) reduced the voltage from 11.1v to 7.57v.
I can adjust this resistance if i need to, this will increase the voltage on the amp but this will increase the amp current usage too.
So.... the amp is receiving ~7.50v on this test. The power LED was ON all the time and protection LED always off. I did not feel heat in anything on the power supply stage or the power stage.
Current usage was something like 1A. But like i said, i can increase that if necessary, this resistante is adjustable.
Please check the image:
Thank you all for the help. I really love this AMP and i will be very happy to fix it.
The heavy resistance i put in series (to reduce the current) reduced the voltage from 11.1v to 7.57v.
I can adjust this resistance if i need to, this will increase the voltage on the amp but this will increase the amp current usage too.
So.... the amp is receiving ~7.50v on this test. The power LED was ON all the time and protection LED always off. I did not feel heat in anything on the power supply stage or the power stage.
Current usage was something like 1A. But like i said, i can increase that if necessary, this resistante is adjustable.
Please check the image:
Thank you all for the help. I really love this AMP and i will be very happy to fix it.
Guys,
This is a regulated power supply?
Because, when we increase or reduce the voltage, the 'hiss' on the toroid changes to higher/lower frequencies instantly.
Very interesting.
This is a regulated power supply?
Because, when we increase or reduce the voltage, the 'hiss' on the toroid changes to higher/lower frequencies instantly.
Very interesting.
Those are gate resistors. The large blue resistors near the output transistors are the emitter resistors.
That said, it appears that you have no drive on one side of the supply. Check R16. The gate resistors look like they overheated. Did you check all of them?
Regulated power supplies with under-damped regulator circuits can cause the power supply transformer to make noise.
That said, it appears that you have no drive on one side of the supply. Check R16. The gate resistors look like they overheated. Did you check all of them?
Regulated power supplies with under-damped regulator circuits can cause the power supply transformer to make noise.
Totally my fault, Perry. I read this on your website on the past and i see my mistake here. I will take another photo soon.
The noise happens when i test the amp with 7A batteries.
The power supply FETs just exploded, they messed up the board with a lot of something like the smoke, i think is that smoke/resin is what you see. I've done my best to clean it up. But no, i did'nt tested them.
I will learn how to test this SMD resistors in the mean while and let you know what i got.
Is necessary to remove them from the board? Because i don't think i can remove this small SMD resistors.
The noise happens when i test the amp with 7A batteries.
The power supply FETs just exploded, they messed up the board with a lot of something like the smoke, i think is that smoke/resin is what you see. I've done my best to clean it up. But no, i did'nt tested them.
I will learn how to test this SMD resistors in the mean while and let you know what i got.
Is necessary to remove them from the board? Because i don't think i can remove this small SMD resistors.
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That's a low value resistor and you may be able to check it in the circuit. Compare the in-circuit readings to the corresponding resistor(s) on the other half of the board.
Looks like we have a problem on almost all gate resistors on the blown side. The values are very high.
On the other side, like you told me to compare, i can see normal resistance on all of them.
But i don't know... my multimeter is not 100% reliable (it is very unstable after a capacitor discharge - we just learn with our mistakes).
I will buy another better multimeter tomorrow to test the resistance better and you let you know.
Thanks.
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Hi friends,
😉
I just bought a cheap multimeter, but it does the job very fine.
This is the part #2 of the AMP, all resistantes are within tolerance:
Here is the part #3. One resistor is for sure opened:
Any suggestions? Should i check if the respective FET/transistor is blown? Or should i just change this resistante and test the amp again?
Thanks!
😉
I just bought a cheap multimeter, but it does the job very fine.
This is the part #2 of the AMP, all resistantes are within tolerance:
An externally hosted image should be here but it was not working when we last tested it.
Here is the part #3. One resistor is for sure opened:
An externally hosted image should be here but it was not working when we last tested it.
Any suggestions? Should i check if the respective FET/transistor is blown? Or should i just change this resistante and test the amp again?
Thanks!
2.45 ohms is likely 2.45k. The resistor is 2.7k but the circuit could be influencing the readings. The emitter resistor reading 8k is likely open. Check the transistor connected to it. The transistor is a bipolar transistor, not an FET.
The 9.3 ohm in the center of the board is likely marked 8.2 ohms and would be out of tolerance and need to be replaced but it wouldn't be likely to cause any serious problems at 9.3 ohms.
The 9.3 ohm in the center of the board is likely marked 8.2 ohms and would be out of tolerance and need to be replaced but it wouldn't be likely to cause any serious problems at 9.3 ohms.
Perry,
Thanks!
Sorry for my ignorance.
Maybe i'm wrong, but the "2.45 Ohm" one shows "362 Ohms":
Look at my multimeter:
Yep. I agree that the circuit maybe is influencing, that makes sense.
I think this 9.3 Ohm resistor is OK. My multimeter cable marks 1.1 Ohm by itself. So, considering the cable resistance, maybe it is okay?
I will test now the bipolar transistor.
If one of them is bad should i change all the transistors on the board?
Thanks!
Sorry for my ignorance.
Maybe i'm wrong, but the "2.45 Ohm" one shows "362 Ohms":
Look at my multimeter:
An externally hosted image should be here but it was not working when we last tested it.
Yep. I agree that the circuit maybe is influencing, that makes sense.
I think this 9.3 Ohm resistor is OK. My multimeter cable marks 1.1 Ohm by itself. So, considering the cable resistance, maybe it is okay?
I will test now the bipolar transistor.
If one of them is bad should i change all the transistors on the board?
Why didn't you subtract the lead resistance from the 9;3 ohm like you did for all of the other low value resistors?
If you didn't subtract the lead resistance, how did you get 0.2 ohms on the 0.33 ohm resistors?
If you didn't subtract the lead resistance, how did you get 0.2 ohms on the 0.33 ohm resistors?
I'm sorry.
Yes. That is because i used two multimeters on my tests and forget to substract from some resistors when i exchanged the multimeter.
Actually, if i substract correctly using my most correct multimeter, i get something like "0.3 Ohm" instead of the "0.2 Ohm" on the images i sent to you.
If you want, i can meter everything again and give you a correct image ASAP.
Thanks for all the help.
Yes. That is because i used two multimeters on my tests and forget to substract from some resistors when i exchanged the multimeter.
Actually, if i substract correctly using my most correct multimeter, i get something like "0.3 Ohm" instead of the "0.2 Ohm" on the images i sent to you.
If you want, i can meter everything again and give you a correct image ASAP.
Thanks for all the help.
Hi.
The faulty resistor have been changed.
Still the same problem. Noises on the toroid and current is very high (20A+).
I reduced the BIAS for both channels (fully counterclockwise).
I've metered all 5w resistances on the board and all of them are within tolerance (considering the cable resistance) now. Like i said before, the non working resistante have been changed.
I will now test the SMD resistors on the power supply stage.
The faulty resistor have been changed.
Still the same problem. Noises on the toroid and current is very high (20A+).
I reduced the BIAS for both channels (fully counterclockwise).
I've metered all 5w resistances on the board and all of them are within tolerance (considering the cable resistance) now. Like i said before, the non working resistante have been changed.
I will now test the SMD resistors on the power supply stage.
Hi.
Something is strange. The resistance readings on the upper part of the power supply shows lower resistances.
The lower part of the power supply shows normal resistances.
Something is strange. The resistance readings on the upper part of the power supply shows lower resistances.
The lower part of the power supply shows normal resistances.
An externally hosted image should be here but it was not working when we last tested it.
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Do the diodes (D3, 4, 5) from the top of the photo read the same as the corresponding diodes at the bottom of the photo?
Check them on diode check as well as ohms.
Did you replace the FETs at the top of the photo?
Check them on diode check as well as ohms.
Did you replace the FETs at the top of the photo?
Perry,
Thanks again for the help. You are incredibly helpful.
No, i didn't, and looks like the FETs are the problem:
You suggest me to change them too?
I'm testing right now the diodes.
Thanks again for the help. You are incredibly helpful.
No, i didn't, and looks like the FETs are the problem:
An externally hosted image should be here but it was not working when we last tested it.
You suggest me to change them too?
I'm testing right now the diodes.
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