cor wrote:Cool that it is a PFC supply. It should have 3 functional blocks: first the AC input with rectifier and PFC switcher, ending in the big caps that store the upconverted DC (usually 200 or 400V). Then comes the PWM controller and switching FET(s) to turn the HV DC into a square wave that drives the transformer.
Third, at the output of the transformer a rectifying diode, filter and shunt with current measurement, feeding back to the PWM controller, together with the voltage feedback. I did not see opto couplers on the pictures. Are they hidden next to the transformer? On the NES they are right next to the transformer.
For fixing, you can check if the PFC stage is still making high voltage DC and then check the final stage for voltage (and current) control and other feedback (on the NES there is also overvoltage and overtemp protection feedback) before you try to attack bringing the PWM stage back to life, since the other parts affect the operation of the PWM controller.
cor wrote:If you get only 160V on the caps then that tells me that the PFC is not working, as that is the normal voltage of rectified 110V AC, not the boosted voltage of a PFC stage, so I would certainly recommend to test if the PFC switching FET is actually working and whether the ML4800 PFC and PWM controller is working.
ah, ok. i have a lot to learn about pfc, having rarely fixed any psus with it, and so far only having to replace bad caps that boiled from high temps in sealed units, or blown fets or output diodes from the caps having died.I noticed that you already found the datasheet with a reference schematic here: http://www.fairchildsemi.com/ds/ML%252FML4800.pdf
The 900V 9A PWM MOSFET 2SK2082 from Fuji Electric can be found in many places, for example: http://pdf1.alldatasheet.com/datasheet-pdf/view/60874/FUJI/2SK2082-01.html and the PFC FET IRFP460A from IR can be found here: http://www.irf.com/product-info/datasheets/data/irfp460a.pdf it is a 500V 20A N-channel MOSFET.
Please note that the voltage of the caps C5 and C?? is 400V, which is a typical PFC boost voltage from anything between 90-260V AC.
The location of the optos and the array of diodes under the transformer looks like the NES setup, but due to the extra complexity of PFC, the controller section is about twice as busy and you have an additional switching FET and rectifying diode.
I love troubleshooting/reverse-engineering a circuit. I have to take care that it does not conflict with my job and other things in life too much...
My interest is that I want to know how things work. I have been known to buy a brand new product and first take it apart, even before plugging it in for the first time (also of course voiding the warranty), but I *had* to know how it worked... Now I mostly buy second hand products so I don't need to bother about warranty when taking them apart, fixing them, improving them if needed...
BTW, I wonder who Willis Lu is, who put his name on the PCB.
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