You'll have to isolate the FETs to test individually. You can do this by lifting the gate leg or sliding the 10 ohm gate resistors off of the pads. Do not apply power with the gates out of the circuit.
As a side note, we need to try defeating the protection circuit on the 'bad' channel when we get past this problem.
As a side note, we need to try defeating the protection circuit on the 'bad' channel when we get past this problem.
With the gate removed from the board I have:
Gate to center:
34.5
OL
72.3
OL
OL
41.5
Gate to right:
34.6
OL
72.0
OL
OL
41.5
Gate to center:
34.5
OL
72.3
OL
OL
41.5
Gate to right:
34.6
OL
72.0
OL
OL
41.5
If this is from the actual gate leg (not the gate pad), the ones that don't red OL are defective.
I'm assuming that this is ohms and that you were not touching the metal part of the probe at any time.
I'm assuming that this is ohms and that you were not touching the metal part of the probe at any time.
yes the gate leg is removed from the pad, this is from the gate leg to the other legs. No I was not touching the meter leads together. I will double check.
Perry,
I got the new FET's installed. I tested the pins and everything now reads OL. Should I mount it back to the heat sink or we should do some testing with it as it sits?
I got the new FET's installed. I tested the pins and everything now reads OL. Should I mount it back to the heat sink or we should do some testing with it as it sits?
Iam not sure. Maybe I touched something or shorted something while reading the voltages? Iam not really sure.
Power it up through the limiter while watching the voltage across the resistor to confirm that it's back to what it was.
The MEHSA insulator will soak some heat so don't leave it powered up outside of the heatsink until you're sure that nothing is heating up.
The MEHSA insulator will soak some heat so don't leave it powered up outside of the heatsink until you're sure that nothing is heating up.
Is the 'good' channel producing clean audio?
When comparing the two channels, initially do as much as you can with resistance/diode-check with no power applied.
Set the bias fully CCW for testing. If the FETs start to heat up, they can quickly fail if not clamped to the heatsink.
When comparing the two channels, initially do as much as you can with resistance/diode-check with no power applied.
Set the bias fully CCW for testing. If the FETs start to heat up, they can quickly fail if not clamped to the heatsink.
I clamped it back into the heatsink to play it safe.
The good channel is good again! The bad one is still bad. I did notice that when I was playing audio on the good channel the voltage went up across the resistors to 2.4* vdc and on the distorted channel it was only around 2.14 vdc
The good channel is good again! The bad one is still bad. I did notice that when I was playing audio on the good channel the voltage went up across the resistors to 2.4* vdc and on the distorted channel it was only around 2.14 vdc
The voltage across the limiter will increase as the amp drives more power into a load. That's normal.
With no power applied, compare the resistance across the various resistors and transistors in the rectangles. measure, the reverse probes and measure again.
With no power applied, compare the resistance across the various resistors and transistors in the rectangles. measure, the reverse probes and measure again.
Power up the amp and compare the voltage on the various transistor terminals (drivers, not outputs). Are they essentially the same for both channels?
Sharpen your probes if you slipped last time you were doing something like this.
Sharpen your probes if you slipped last time you were doing something like this.
I was testing the transistors on the rail and I found that Q17 had different readings from Q7 could there be an issue with one of them?