Hi to all... This is my first post (apart the presentation 
)
I've found this forum searching for info for some chips on a power supply that i'm trying to repair, and seem a good place to learnn something (and maybe reapir my èsu )
I have this SMPS psu of an hp deskjet plotter that is active PFC, and have 2 different trasformers to do different voltages, one do low tensions (+3.3, +5) and the other do the 'high' tensions (12,24,36). The high tension side isn't working.
First of all, on the electronic side i've not found anythying wrong/burned (only no tension on the secondary, neither on startup), but i think that the primary of the transformer is gone, as on one pin i can't find continuity with any other pin.
This is the first time that i try to reapir a 'recent' power supply (while in past i've successfully repaired different 'standard' smps). Apart active pfc circuit that i've marginally understood, i've not still fully understood the primary of the 'high voltage' tansformer. It has 2 primary coils (with 3 pins), and 2 mosfets driving it. One pin of the primary (pin marked 6 on the pcb) is connected to gnd and has no continuity to any other pin (strange), another pin on the primary side (pin 7) is connected to the drain of a mosfet q14 (and the source of the mosfet goes to gnd throught a resistor), the last pin (pin 3) goes to the source of the second mosfet q13 (and the drain goes to ~+300v, here in italy we have 220 main).
Why there are 2 mosfets driving it?
It's possible that only the transformer is damaged, as i've not found any other problem (mosfet, diodes, etc)? This would be the first time that i find an smps trasformer damaged...
Really thanks for the help!
)I've found this forum searching for info for some chips on a power supply that i'm trying to repair, and seem a good place to learnn something (and maybe reapir my èsu
)I have this SMPS psu of an hp deskjet plotter that is active PFC, and have 2 different trasformers to do different voltages, one do low tensions (+3.3, +5) and the other do the 'high' tensions (12,24,36). The high tension side isn't working.
First of all, on the electronic side i've not found anythying wrong/burned (only no tension on the secondary, neither on startup), but i think that the primary of the transformer is gone, as on one pin i can't find continuity with any other pin.
This is the first time that i try to reapir a 'recent' power supply (while in past i've successfully repaired different 'standard' smps). Apart active pfc circuit that i've marginally understood, i've not still fully understood the primary of the 'high voltage' tansformer. It has 2 primary coils (with 3 pins), and 2 mosfets driving it. One pin of the primary (pin marked 6 on the pcb) is connected to gnd and has no continuity to any other pin (strange), another pin on the primary side (pin 7) is connected to the drain of a mosfet q14 (and the source of the mosfet goes to gnd throught a resistor), the last pin (pin 3) goes to the source of the second mosfet q13 (and the drain goes to ~+300v, here in italy we have 220 main).
Why there are 2 mosfets driving it?
It's possible that only the transformer is damaged, as i've not found any other problem (mosfet, diodes, etc)? This would be the first time that i find an smps trasformer damaged...
Really thanks for the help!
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