Came in- PS blown looks like reverse polarity.
Installed new components, PS fets not installed yet gate drive good square wave just low voltage like 3V. Install FETS gate drive looks very unstable. Drawing high current (Rectifiers are not installed at this point)
I did replace the C2045. Does the 3843B feed PWM to the 2045? Pin 6 on the 3843 seems to have the unstable gate drive waveform on it.
Installed new components, PS fets not installed yet gate drive good square wave just low voltage like 3V. Install FETS gate drive looks very unstable. Drawing high current (Rectifiers are not installed at this point)
I did replace the C2045. Does the 3843B feed PWM to the 2045? Pin 6 on the 3843 seems to have the unstable gate drive waveform on it.
Yes, Pin 6 3843B drives the 2045 gate drivers.
Reinstall the rectifiers. Remove the PS FETs. This is how I normally check these amps.
Check with a scope the Sawtooth and Drive on Pin 4 and 6 3843B and post screenshots.
Not sure this is reverse polarity incident, and may be under gauged and/or CCA power cable and pushing the amp to hard. This will starve the PS FETs and the resulting back EMF when the FETs fail will exceed the reverse bias rating of the input diode and the input filter caps can swell and fail. In a reverse polarity situation the diode will conduct and bypass the power supply. I mention this so that the customer can make an informed decision, when choosing the proper power cables.
Reinstall the rectifiers. Remove the PS FETs. This is how I normally check these amps.
Check with a scope the Sawtooth and Drive on Pin 4 and 6 3843B and post screenshots.
Not sure this is reverse polarity incident, and may be under gauged and/or CCA power cable and pushing the amp to hard. This will starve the PS FETs and the resulting back EMF when the FETs fail will exceed the reverse bias rating of the input diode and the input filter caps can swell and fail. In a reverse polarity situation the diode will conduct and bypass the power supply. I mention this so that the customer can make an informed decision, when choosing the proper power cables.
I did reinstall rectifiers and is now blowing 25 amp fuse that I have inline. Is that 25amp fuse enough to get this amp started up?
Next I will remove PS Fets and probe as Papa advised.
Next I will remove PS Fets and probe as Papa advised.
25 amps is way more than u need to start it. 2 amps is probably more than enough without fets in.
Are u using a battery or do u have a beefy supply? I would drop the fuse to at least 15 or 10 maybe even 5 if ur using a battery.
This amp will have a significant in rush current. Not sure if it exceeds 25 amps. I will test that tommorow.
Try w/o the FETs and screenshot Pins 4,6 and the gate pads. Also DC voltages around the UC3843.
Try w/o the FETs and screenshot Pins 4,6 and the gate pads. Also DC voltages around the UC3843.
Replaced the 3843B with a known working one and it still has no sawtooth on Pin 6.
Pin 1 .7v
Pin 2 2.8v
Pin 3 9v
Pin 4 sawtooth 2.5v peak
Pin 5 0v
Pin 6 0v
Pin 7 11.6v
Pin 8 4.9v
Pin 1 .7v
Pin 2 2.8v
Pin 3 9v
Pin 4 sawtooth 2.5v peak
Pin 5 0v
Pin 6 0v
Pin 7 11.6v
Pin 8 4.9v
Pin 6 should have a short duration pulse, maybe 20% duty cycle.You may have to adjust time base to capture it
Post screenshots of pin 4, pin 6 and gate pads
Post screenshots of pin 4, pin 6 and gate pads
I'm not sure but it may be a 10 ohm resistor tied between +12v/Batt and IC8-Pin 9/ZD9-18v zener/C91-47uF 16V. I will need to verify this and will get back to you.
OK replaced the 10 ohm resistor. Got everything straightened out with the PS fet drive. Put fets back in. still will not power up on my low current supply. On my higher current supply it pops a 35 amp fuse.
Output Fets read ok. PS fets read ok.
Output Fets read ok. PS fets read ok.
This is a 10 ohm resistor. Must likely blown due to a shorted ZD9-18 vote zener or IC8
Have you looked at IC8 and ZD9?
Have you looked at IC8 and ZD9?
Replaced IC8. ZD9 checks ok in circuit with my diode checker.
If I power with a current limiter (to keep from blowing the 10 ohm resistor) it is clear that the PS Fets are not getting drive. If I remove them from circuit the drive looks perfect.
If I power with a current limiter (to keep from blowing the 10 ohm resistor) it is clear that the PS Fets are not getting drive. If I remove them from circuit the drive looks perfect.