Figured I would just start a different thread for this issue but is part of the Yaskawa VFD I am working on in my other thread. The VFD had been powering up normally without issue aside from the microcontroller output issue. Well, went to do some more circuit testing and the small PSU that runs the main PC board decided to take a break. Need a little help figuring this one out.
So... I have provided pics of the DC-DC PSU. this PSU receives 'unregulated' DC power from another board in which only a full bridge rectifier and capacitor reside. Why they did not just put this all in one PSU is beyond me! So the voltage going to the DC-DC board is 1.414* mains voltage or about 296VDC, but I measured right at 1VAC on those leads going to the supply. Is that acceptable ripple? I did not expect to see that much but its just a rectifier and cap feeding it.
If that is not the issue, I am a little lost because I expected to find a bad capacitor and so far all my ESR testing is showing things good right not.
So... Since I JUST tested that DC-DC board only 30min earlier, I know for a fact it was providing clean power. Voltages were reasonable and ripple was around 1mV. After it failed, I tested the rail for voltages and all were absent. I unplugged all load from the PSU and voltages came back a bit but still not right and reading low. Its like the PSU is straining over itself. I have seen it with bad caps in a SMPS but I cannot spot the issue here.
The big component on the sink by itself is a mosfet. I believe it is controlled by that daughter board as the switcher to bring the voltage down. I pulled the big cap hoping for an easy fix but it tests ok for now. I use ESR and a capacitance tester. I should probably up my game because I know some tests just don't show a bad cap. These caps are running north of 300V.
So... I have provided pics of the DC-DC PSU. this PSU receives 'unregulated' DC power from another board in which only a full bridge rectifier and capacitor reside. Why they did not just put this all in one PSU is beyond me! So the voltage going to the DC-DC board is 1.414* mains voltage or about 296VDC, but I measured right at 1VAC on those leads going to the supply. Is that acceptable ripple? I did not expect to see that much but its just a rectifier and cap feeding it.
If that is not the issue, I am a little lost because I expected to find a bad capacitor and so far all my ESR testing is showing things good right not.
So... Since I JUST tested that DC-DC board only 30min earlier, I know for a fact it was providing clean power. Voltages were reasonable and ripple was around 1mV. After it failed, I tested the rail for voltages and all were absent. I unplugged all load from the PSU and voltages came back a bit but still not right and reading low. Its like the PSU is straining over itself. I have seen it with bad caps in a SMPS but I cannot spot the issue here.
The big component on the sink by itself is a mosfet. I believe it is controlled by that daughter board as the switcher to bring the voltage down. I pulled the big cap hoping for an easy fix but it tests ok for now. I use ESR and a capacitance tester. I should probably up my game because I know some tests just don't show a bad cap. These caps are running north of 300V.