Before the I blew the mosfets, the amp was in my car (12v from car battery). Now I use a desktop pc power supply for testing. The amp makes the power supply shut down when I connect the remote. I think the psu detects a short in the amp circuit and automatically shuts itself off.
I can get all the three current limiters you mentioned, but where to put the limiter is the part of the puzzle I don't know. Can you please pinpoint for me the current limiter on the schematic diagram so that I can go directly and avoid the risk of going more wrong.
I know it's a kind of stupid thing to ask from a beginner.
Thanks my brother.
Herein the schematic
I know it's a kind of stupid thing to ask from a beginner.
Thanks my brother.
Herein the schematic
The current limiter goes in the B+ line between the power supply and the amplifier.
If you don't have an amp meter on the power supply, you'll have to measure the voltage across the limiter to see an increase in current draw. In amps that use a higher valuse source/emitter resistor, you can measure the voltage across those resistors for each channel but the extremely low value of the ones in this amp make that difficult.
Before replacing the parts that failed (besides those resistors), did the other channel work?
Did the output transistors fail?
If you don't have an amp meter on the power supply, you'll have to measure the voltage across the limiter to see an increase in current draw. In amps that use a higher valuse source/emitter resistor, you can measure the voltage across those resistors for each channel but the extremely low value of the ones in this amp make that difficult.
Before replacing the parts that failed (besides those resistors), did the other channel work?
Did the output transistors fail?
The left channel is working now with the MOSFETs of the right channel is taken off the board. I think I'm going to adjust the bias of the right channel referring to the bias of the left channel based on resistance.
the bias of the left channel (working channel) is now in the middle of the way and its resistance is 1k ohms which is also half of the value of resistance indicated in the schematic.
Am I on the right path doing so before fitting the new MOSFETs?
the bias of the left channel (working channel) is now in the middle of the way and its resistance is 1k ohms which is also half of the value of resistance indicated in the schematic.
Am I on the right path doing so before fitting the new MOSFETs?
If that gets the bias set right, you should buy a lottery ticket.
Changing any components, and especially the output transistors with non-matching replacements, requires a different bias setting (compared to the other channel).
If the source resistors opened (value after heating well higher than 0.03 ohms). there may have been damage to the protection circuit. Those components need to be checked before you install the outputs. To check the resistors, you may need to remove the resistors that you just installed. The resistors that often burn are connected to those low value resistors and will skew the readings of the small resistors.
Changing any components, and especially the output transistors with non-matching replacements, requires a different bias setting (compared to the other channel).
If the source resistors opened (value after heating well higher than 0.03 ohms). there may have been damage to the protection circuit. Those components need to be checked before you install the outputs. To check the resistors, you may need to remove the resistors that you just installed. The resistors that often burn are connected to those low value resistors and will skew the readings of the small resistors.
The output transistors on the right are identical to the ones on the right (both sfp9540 and irf540) as well as all other resistors of both channels. For this regard, I'm going to replace the outputs with the exact same label or at least the exact same input, output, and amps values.
For the protection circuit, is it a shared circuit btw both channels? Meaning, it controls the channels or sends signals to them from the same electrical components ( including lm339d, tl494c, and all other resistors, capacitors, and diodes).
I wish I'm clear enough.
I didn't replace any resistors, by the way. I only measure them out of the circuit board and refitted them. It was hard to read those 0.03 ohms as you said.
For the protection circuit, is it a shared circuit btw both channels? Meaning, it controls the channels or sends signals to them from the same electrical components ( including lm339d, tl494c, and all other resistors, capacitors, and diodes).
I wish I'm clear enough.
I didn't replace any resistors, by the way. I only measure them out of the circuit board and refitted them. It was hard to read those 0.03 ohms as you said.
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To have transistors that would not (may not) need a different bias setting, they would have to have been produced from the same batch as the 20 year old originals and even then, the bias settings may have been different due to other components in the circuit.
The protection circuits for over-current are localized in these amps. I've highlighted them for one channel. The other channel is the same. The two resistors across the 0.03 ohm resistors are the first you need to check.
The protection circuits for over-current are localized in these amps. I've highlighted them for one channel. The other channel is the same. The two resistors across the 0.03 ohm resistors are the first you need to check.
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