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Post by haroldohio on Aug 4, 2013 18:41:17 GMT
I’m here looking for some advice and guidance to trouble shooting my Bravo Audio V2.
The unit no longer has audio output and the LEDs do not light up. One side of the tube will glow and the other does not. One voltage regulator gets very hot. The other regulator doesn’t and neither do the MOSFETs. So far I have used my multimeter to test different points on the PCB. I do have 24v at the input and various places of the board. I have checked resistance across all resistors and none of them fail. I have voltage on both side of the LEDs but neither will light up. I have done a diode check on both LEDs and get a reading but, have no base value to compare. I can find a pinout diagram of the tube but have no idea what values I should be seeing. I’m having trouble finding any relevant information to trouble shoot any of this.
I figured I’d try some my luck at replacing some pieces on the PCB. I went to radio shack and bought a new power switch, both voltage regulators, and recommended “upgraded” MOSFET transistors IRF510.
I started with the on/off switch and had no change. Next, the voltage regulators were swapped out and no change still. The MOSFETs were changed out lastly. Now the MOSFET that is in series with the regulator gets hot. I can also hear audio in the right channel but it is very faint.
I’m very handy with a multimeter and soldiering but my experiences are limited to the automotive world. I would like the try to repair the unit if I can to avoid buying another.
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Post by Deleted on Aug 5, 2013 11:26:20 GMT
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Post by Deleted on Aug 5, 2013 22:18:59 GMT
Some additional information. The red LED will have a typical forward voltage when conducting, of between 1.5V and 1.8V, with later types mainly around 1.8V at say a couple of mA current.. The 2N3906 transistor will have a base emitter voltage of a little over 600 mV . Subtracting 600mV from the 1.8V gives approximately 1.2V across the 3K0 emitter resistor, This sets the current through the 2N3906 current source to give the desired Anode Current of the valve. The LM317 is configured as a current source. It has a typical reference voltage of a little over 1.2V. If the resistor was 1.2 ohms, the constant current supplied would be 1A. The present resistor value is such that the correct heater current for the valve is provided. Perhaps others more familiar with this design can assist here ? ( I gave up on valves more than 30 years ago)
Alex
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