Fluctuating Voltages

Hello, I am working on a SMPS from a PC monitor. Voltages across the circuit are all wrong and not only that but they are fluctuating as well. I started by checking the AC voltage from the outlet through the monitor power cable, it is a steady 221Vac (I am in South America, things are a little more dangerous here..lol) but when i plug in the monitor, ac voltage starts fluctuating from 215Vac to 221Vac and all voltages in between. I can trace this problem from the ac plug, all the way to the SMPS controller, bridge rectifier and main filter cap as well. So the problem occurs both on the ac and dc sides of the PS. Another thing that is happening is that if i measure voltage on the chopper resistor=B4s Drain i get over a thousand volts!!!!! DMM goes blank....I've compare the MOSFET to one that is working and this one seems fine. I thought that the chopper transformer was shorted but I=B4ve replaced it with a good one and the same thing happens. Can any one help me?

Thank you...

Hello, I am working on a SMPS from a PC monitor. Voltages across the circuit are all wrong and not only that but they are fluctuating as well. I started by checking the AC voltage from the outlet through the monitor power cable, it is a steady 221Vac (I am in South America, things are a little more dangerous here..lol) but when i plug in the monitor, ac voltage starts fluctuating from 215Vac to 221Vac and all voltages in between. I can trace this problem from the ac plug, all the way to the SMPS controller, bridge rectifier and main filter cap as well. So the problem occurs both on the ac and dc sides of the PS. Another thing that is happening is that if i measure voltage on the chopper resistor´s Drain i get over a thousand volts!!!!! DMM goes blank....I've compare the MOSFET to one that is working and this one seems fine. I thought that the chopper transformer was shorted but I´ve replaced it with a good one and the same thing happens. Can any one help me?

The high voltage at the transistor is normal, it's caused by the inductive kick of the transformer, I've never actually seen a switching transformer fail so that's never really been a suspect.

How are the capacitors on the output side? The power supply should easily compensate for the fluctuating input voltage.

Hello, I am working on a SMPS from a PC monitor. Voltages across the circuit are all wrong and not only that but they are fluctuating as well. I started by checking the AC voltage from the outlet through the monitor power cable, it is a steady 221Vac (I am in South America, things are a little more dangerous here..lol) but when i plug in the monitor, ac voltage starts fluctuating from 215Vac to 221Vac and all voltages in between. I can trace this problem from the ac plug, all the way to the SMPS controller, bridge rectifier and main filter cap as well. So the problem occurs both on the ac and dc sides of the PS. Another thing that is happening is that if i measure voltage on the chopper resistor´s Drain i get over a thousand volts!!!!! DMM goes blank....I've compare the MOSFET to one that is working and this one seems fine. I thought that the chopper transformer was shorted but I´ve replaced it with a good one and the same thing happens. Can any one help me?

Thank you...

is you meter a true RMS voltmeter or a peak reading meter?

It is a cheap piece of $%=B7" meter...lol.... I=B4m serious tho...

It is a cheap piece of $%=B7" meter...lol.... I=B4m serious tho...

Hello and thanks. You say that the high voltage is normal...but is it normal if it stays like that always? If it is caused by the inductive kick of the trans...should it not just be a temporary thing? And yes, all caps SEEM fine, all i have to check them is my little piece of $&=B7% DMM.