This amp has 2 Optocoupler driver cards on the output.
(photo attached, pin configuration from left to right)
Pin 1: GND
Pin 2: Input PWM drive (coming from a 74HC00 IC)
Pin 3: Power supply transformer PWM
Pin 4: VCC
Pin 5: Output PWM drive for bank 1
Pin 6: Output PWM drive for bank 2
One side of the amp does not want to create an OUTPUT drive PWM going to the gates of the IRF640N's. Even putting in a 100% good driver card results in no usable PWM gate drive.
The driver card receives a PWM drive input on Pin 2.
Also the power supply PWM on Pin 3 is present.
The GND and VCC is also present on Pin 1 and 4.
There is just no output on Pin5 and Pin6
Almost every part on the output PWM circuit has been replaced (all the 2x and 2t transistors, 74HC00, 6n137 optocoupler). All resistors on the driver card has been checked and are OK.
(photo attached, pin configuration from left to right)
Pin 1: GND
Pin 2: Input PWM drive (coming from a 74HC00 IC)
Pin 3: Power supply transformer PWM
Pin 4: VCC
Pin 5: Output PWM drive for bank 1
Pin 6: Output PWM drive for bank 2
One side of the amp does not want to create an OUTPUT drive PWM going to the gates of the IRF640N's. Even putting in a 100% good driver card results in no usable PWM gate drive.
The driver card receives a PWM drive input on Pin 2.
Also the power supply PWM on Pin 3 is present.
The GND and VCC is also present on Pin 1 and 4.
There is just no output on Pin5 and Pin6
Almost every part on the output PWM circuit has been replaced (all the 2x and 2t transistors, 74HC00, 6n137 optocoupler). All resistors on the driver card has been checked and are OK.
Attachments
There is 0v across Pin3 and Pin4
Measured from GND:
Pin3 is 70.9v
Pin4 is 70.9v
The 6n137 optocoupler outputs a PWM wave.
Measured from GND:
Pin3 is 70.9v
Pin4 is 70.9v
The 6n137 optocoupler outputs a PWM wave.
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Finally I found the problem 😀
The 15V zener diodes attached to the gate resistors were leaking.
Now, the 2 output drive cards output a PWM gate drive.
Just one output card outputs a wobbly PWM gate drive (first attached photo). I imagine this could be the reason why the output fets of this amplifier died.
This driver card recieves a wobbly PWM wave from the power supply transformer on Pin3 (second attached photo).
The transformers are driven correctly.
The 15V zener diodes attached to the gate resistors were leaking.
Now, the 2 output drive cards output a PWM gate drive.
Just one output card outputs a wobbly PWM gate drive (first attached photo). I imagine this could be the reason why the output fets of this amplifier died.
This driver card recieves a wobbly PWM wave from the power supply transformer on Pin3 (second attached photo).
The transformers are driven correctly.
Attachments
Yes, this is true, sorry, forgot to mention.
This is the other driver board (not the driver board from the start of this thread)
Pins of the driver card:
Pin 1: GND
Pin 2: Input PWM drive (coming from a 74HC00 IC)
Pin 3: Power supply transformer PWM
Pin 4: 0.003v
Pin 5: Output PWM drive for bank 3
Pin 6: Output PWM drive for bank 4
The multimeter reads -0.003v (black probe on Pin3, red probe on Pin4)
Measured to GND
Pin3 is 0.000v
Pin4 is 0.003v
This is the other driver board (not the driver board from the start of this thread)
Pins of the driver card:
Pin 1: GND
Pin 2: Input PWM drive (coming from a 74HC00 IC)
Pin 3: Power supply transformer PWM
Pin 4: 0.003v
Pin 5: Output PWM drive for bank 3
Pin 6: Output PWM drive for bank 4
The multimeter reads -0.003v (black probe on Pin3, red probe on Pin4)
Measured to GND
Pin3 is 0.000v
Pin4 is 0.003v
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Both driver boards are identical (photo attached)
Just the DC input voltage on Pin3 and Pin4 measured to GND is different
Just the DC input voltage on Pin3 and Pin4 measured to GND is different
Attachments
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I rewound the transformer winding. Still the wobbly oscillation is present on Pin3.
With the driver card removed, the transformer PWM with oscillation is still present on Pin3.
I suspect the problem is the transformer, but rewinding did not make a difference.
With the driver card removed, the transformer PWM with oscillation is still present on Pin3.
I suspect the problem is the transformer, but rewinding did not make a difference.
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You state the you have PWM on pin 3. Is it at the power supply frequency (25k?) or at the oscillation frequency of the output carrier (100k?)?
Pin 3 is at the power supply frequency.
Pin 3 is directly connected to a seperate 4turn coil on the power supply transformer. I rewound this coil. Oscillation is still present.
Pin 3 is directly connected to a seperate 4turn coil on the power supply transformer. I rewound this coil. Oscillation is still present.
This amp is slightly different from what I was using as a reference.
The winding that you're referring to is rectified on the driver board. Measuring from pin 4 to the input of the 5v regulator should give you the DC that I was expecting.
Pin 4 of one driver board (low-side) connects to the negative rail. Is that correct?
Pin 4 of the other driver board connects to the source leg of the high-side driver board. Is that correct?
The winding that you're referring to is rectified on the driver board. Measuring from pin 4 to the input of the 5v regulator should give you the DC that I was expecting.
Pin 4 of one driver board (low-side) connects to the negative rail. Is that correct?
Pin 4 of the other driver board connects to the source leg of the high-side driver board. Is that correct?
Correct 😀
Pin 4 of the low-side driver board connects to negative rail (Source leg of the IRF640N)
Pin 4 of the high side driver board connects to the Source leg of the IRF640N.
The driver board which outputs a wobbly PWM gate drive is the high side section.
Pin 4 of the low-side driver board connects to negative rail (Source leg of the IRF640N)
Pin 4 of the high side driver board connects to the Source leg of the IRF640N.
The driver board which outputs a wobbly PWM gate drive is the high side section.
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The high-side is floating with the source of the high-side FETs. A slight bit of noise or hum may cause what you're seeing.
Do you mean the hum which is present at Pin3?
As reference from the same good working amplifier, this oscillation should not be present.
When I first opened this amp, it had broken output fets.
There was no output PWM drive present coming from the 74HC00.
The 6N137 optocouplers and a lot of 2x and 2t transistors were killed as well.
The 15v zener diodes which are connected to the gate resistors were also killed.
Currently the driver boards output a PWM gate drive. Just the high side driver board outputs the strange wobbly oscillation. To check how this oscillation would react on switching fets I tried 1 fet per bank with a very low amount of current.
The amplifier is instantly killing the output fets at this point when they are installed (in all 4 banks, also the good looking low side banks). Even with only 2amps of PS current.
When the amp powers up (one fet per bank installed) the amplifier gives a single ticking sound and the output fets are instantly killed.
As reference from the same good working amplifier, this oscillation should not be present.
When I first opened this amp, it had broken output fets.
There was no output PWM drive present coming from the 74HC00.
The 6N137 optocouplers and a lot of 2x and 2t transistors were killed as well.
The 15v zener diodes which are connected to the gate resistors were also killed.
Currently the driver boards output a PWM gate drive. Just the high side driver board outputs the strange wobbly oscillation. To check how this oscillation would react on switching fets I tried 1 fet per bank with a very low amount of current.
The amplifier is instantly killing the output fets at this point when they are installed (in all 4 banks, also the good looking low side banks). Even with only 2amps of PS current.
When the amp powers up (one fet per bank installed) the amplifier gives a single ticking sound and the output fets are instantly killed.
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Connecting a load to the speaker terminals makes no difference in gate drive for the Hi or Low side.