One of the opamps was defective and that caused the noise in signal.
After removing the opamp I get clean audio on one end of the 750 ohms resistors. Relay does not still engage and on output filter inductor I get clean audio with about 2 volt amplitude. Seems low. I will replace the missing opamp and see what happens then.
After removing the opamp I get clean audio on one end of the 750 ohms resistors. Relay does not still engage and on output filter inductor I get clean audio with about 2 volt amplitude. Seems low. I will replace the missing opamp and see what happens then.
Installed a opamp in the place of the missing opamp and now I get proper audio on output filter inductor. Sinewave with 30V amplitude and that was not at full volume. When connecting a speaker wires to output inductors I get nice audio from the speaker.
Relay still does not want to co-operate though
There are two pins on the relay which have 11V, one of them is supposed to go down to 0V for the relay to work. I cant trace what is connected to those pins, Id have to remove the relay to see.
Relay still does not want to co-operate though
There are two pins on the relay which have 11V, one of them is supposed to go down to 0V for the relay to work. I cant trace what is connected to those pins, Id have to remove the relay to see.
There's a transistor near the 330uf cap that drives one terminal to ground.
Confirm that you don't read anything near 0 ohms across the diode for the relay (kust behind the relay). If it's OK, check that transistor. In your amp, it appears to be a TO-220. I've never seen a TO-220 case transistor there so someone may have installed the wrong transistor.
Confirm that you don't read anything near 0 ohms across the diode for the relay (kust behind the relay). If it's OK, check that transistor. In your amp, it appears to be a TO-220. I've never seen a TO-220 case transistor there so someone may have installed the wrong transistor.
TO-220 transistor seems to be from the factory by the looks of soldering and box drawn on the board. That transistor is in working order. Has 1V, 11V and 0V on its legs.
Removed the relay and managed to break it, they use some weird solder on this amp, my iron does not want to chew through it, need to get more of that chip-quik.
Traces from the pins of relay go to the center of the board in the power supply section, one trace connects to one end of a diode and a cap, the other trace to another end of the same components. One end of these is connected to center leg of the TO-220 transistor mentioned earlier. Other end of the diode and cap is connected to a transistors center leg, transistor is located near 494. This transistor has 10,5V-11V on all of its legs, some minor differences. It is not shorted though. With that transistor out of the circuit, pad for first leg of that transistor has 12,5V pad for center leg has 0V. Without that transistor amp does not power up properly, power LED even does not come on.
I will try another transistor in its place to see if I still get 11V on its center leg.
Or do I get it wrong? TO-220s center leg is supposed to go down to 0v?
Removed the relay and managed to break it, they use some weird solder on this amp, my iron does not want to chew through it, need to get more of that chip-quik.
Traces from the pins of relay go to the center of the board in the power supply section, one trace connects to one end of a diode and a cap, the other trace to another end of the same components. One end of these is connected to center leg of the TO-220 transistor mentioned earlier. Other end of the diode and cap is connected to a transistors center leg, transistor is located near 494. This transistor has 10,5V-11V on all of its legs, some minor differences. It is not shorted though. With that transistor out of the circuit, pad for first leg of that transistor has 12,5V pad for center leg has 0V. Without that transistor amp does not power up properly, power LED even does not come on.
I will try another transistor in its place to see if I still get 11V on its center leg.
Or do I get it wrong? TO-220s center leg is supposed to go down to 0v?
If you have 1v on the first leg, 11v on the second and 0 on the third, the transistor is defective (assuming that it's a standard BJT).
The center pin had no voltage on it because the relay was out of the circuit.
Yes, the center leg of the TO-220 transistor is supposed to ground one terminal of the relay coil.
The center pin had no voltage on it because the relay was out of the circuit.
Yes, the center leg of the TO-220 transistor is supposed to ground one terminal of the relay coil.
TO-220 transistor (IRF530N) was defective, measured OK, but when replaced with another transistor I get 0 and 11 V on coil pads of relay.
Now I have another problem. I cant find suitable relay. This one would work:
http://www.schukat.com/schukat/pdf.nsf/index/2510662A3024746CC1257735003D5677/$file/FRA2_.pdf
?
I cant find any mention of AC voltage, is that a problem?
Pinout is different, I will have to use jumper wires.
Now I have another problem. I cant find suitable relay. This one would work:
http://www.schukat.com/schukat/pdf.nsf/index/2510662A3024746CC1257735003D5677/$file/FRA2_.pdf
?
I cant find any mention of AC voltage, is that a problem?
Pinout is different, I will have to use jumper wires.
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