Hi all, I have a skar RP2000.1 that is kicking my butt.
All output fets and power supply fets have been pulled. All drive transistors that drive the TL494's output to the gates of the power supply fets have been swapped as the originals were toasted.
When I attempt to power up I can see the gate drive being setup for a fraction of a second then it shuts down. Pins on the tl494 that raise red flags are pin 3 and 16. Both start out at 0v at power up and then swing to 3.81v about 2 seconds after REM is given voltage.
Here are all the TL494 pin voltages. (Second voltage if noted is after 2+ seconds of power being on rem+)
Pin 1: 0
Pin 2: 3.81
Pin 3: 0, 3.81
Pin 4: 3.81, 0
Pin 5: 1.05 (weak oscillation)
Pin 6: 2.59
Pin 7: 0
Pin 8: 11
Pin 9: gatedrive for a quick moment, 0
Pin 10: gatedrive for a quick moment, 0
Pin 11: 11
Pin 12: 11
Pin 13: 3.81
Pin 14: 3.81
Pin 15: 1.37
Pin 16: 0, 3.80
There is also a nearby LM393 whose pinout reads:
Pin 1: 0, 3.65
Pin 2: 3.81
Pin 3: 5.67
Pin 4: 0
Pin 5: 1.86
Pin 6: 1.29
Pin 7: 0, 3.81
Pin 8: 11v
Attached is a picture of the area.
All output fets and power supply fets have been pulled. All drive transistors that drive the TL494's output to the gates of the power supply fets have been swapped as the originals were toasted.
When I attempt to power up I can see the gate drive being setup for a fraction of a second then it shuts down. Pins on the tl494 that raise red flags are pin 3 and 16. Both start out at 0v at power up and then swing to 3.81v about 2 seconds after REM is given voltage.
Here are all the TL494 pin voltages. (Second voltage if noted is after 2+ seconds of power being on rem+)
Pin 1: 0
Pin 2: 3.81
Pin 3: 0, 3.81
Pin 4: 3.81, 0
Pin 5: 1.05 (weak oscillation)
Pin 6: 2.59
Pin 7: 0
Pin 8: 11
Pin 9: gatedrive for a quick moment, 0
Pin 10: gatedrive for a quick moment, 0
Pin 11: 11
Pin 12: 11
Pin 13: 3.81
Pin 14: 3.81
Pin 15: 1.37
Pin 16: 0, 3.80
There is also a nearby LM393 whose pinout reads:
Pin 1: 0, 3.65
Pin 2: 3.81
Pin 3: 5.67
Pin 4: 0
Pin 5: 1.86
Pin 6: 1.29
Pin 7: 0, 3.81
Pin 8: 11v
Attached is a picture of the area.
Attachments
Check the application notes, or simply change the chips, they are cheap.
The 393 compares the voltages to those needed, then it allows the 494 to drive the SMPS chopper transistors.
And sometimes it takes so long to find the fault that it is easier to change the board.
You need to check all the components on the board, a schematic would be useful, also an analog meter, digital ones jump around.
The 393 compares the voltages to those needed, then it allows the 494 to drive the SMPS chopper transistors.
And sometimes it takes so long to find the fault that it is easier to change the board.
You need to check all the components on the board, a schematic would be useful, also an analog meter, digital ones jump around.
2 things.
The first is that the 5v regulated output of the 494 is low. That would indicate that the IC is either defective or something is pulling the 5v down.
Some of these amps have a power supply protection, of sorts. They will generate output pulses and look for rail voltage. If there is no rail voltage, the drive shuts down.
I'd suspect that the 494 may be defective but if it still won't produce pulses, try installing one FET in each PS bank to see if it will power up. I'd do this while under current limiting since there could be other drive problems.
The first is that the 5v regulated output of the 494 is low. That would indicate that the IC is either defective or something is pulling the 5v down.
Some of these amps have a power supply protection, of sorts. They will generate output pulses and look for rail voltage. If there is no rail voltage, the drive shuts down.
I'd suspect that the 494 may be defective but if it still won't produce pulses, try installing one FET in each PS bank to see if it will power up. I'd do this while under current limiting since there could be other drive problems.
Thank you Perry those were the exact issues!!
New TL494 installed with no fets, pin 14 read 4.74v. Installed 1 fet per bank and wham power supply is up and running making food rail voltage! Thank you!!!
However this is a segway into a recurrent problem I'm having with these type 4 class D amps. The PWM drive is present on all gate pads however it is way way way too weak to drive the 640Ns. (P2P voltage of 1.2 to 2.4v and it varies all over the place.)
Could this be a result of the tl072 and the LM6172 being on the fritz? Output on pin1 on the 6172 (which feeds pin1 on the 74hc00d) seems to vary from 4.7v P2P down to 1.2v as the ICs warm up.
New TL494 installed with no fets, pin 14 read 4.74v. Installed 1 fet per bank and wham power supply is up and running making food rail voltage! Thank you!!!
However this is a segway into a recurrent problem I'm having with these type 4 class D amps. The PWM drive is present on all gate pads however it is way way way too weak to drive the 640Ns. (P2P voltage of 1.2 to 2.4v and it varies all over the place.)
Could this be a result of the tl072 and the LM6172 being on the fritz? Output on pin1 on the 6172 (which feeds pin1 on the 74hc00d) seems to vary from 4.7v P2P down to 1.2v as the ICs warm up.
I don't know about the sub of the TL072 in these amps. Try it.
The drive voltage is determined by the 6N137 optocouplers. Do you have 5.0v across pins 5 and 8?
What make/model scope do you have?
The drive voltage is determined by the 6N137 optocouplers. Do you have 5.0v across pins 5 and 8?
What make/model scope do you have?