DC 500V power generator fails - Page 1
Forum section: electronics / repair

author: dxxp
author_rank: Newbie
timestamp: December 23, 2023, 01:32:52 am
content: This power supply is for plasma cleaning and has no output.+/-15V, generated from separated two PSs and connected via fuses, are measured from the main board.No output is measured from 10V output terminal which supplys primary voltage into the transformer.When I checked between primary 10V output and GND, they are short each other.I am not quite sure but IRF640 N channel mosfet which drain is directly connected to primary output. It seems to have burning mark like attached picture.I don't have proper soldering tools to remove it but I will prepare tool and spare part and will try to repair it.I share one more picture of the front and back side of PCB.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 23, 2023, 01:17:36 pm
content: show us the x-former markings on itseems a simple smps circuit

author: wasedadoc
author_rank: Super Contributor
timestamp: December 23, 2023, 02:02:19 pm
content: Looks like that IRF640 has been replaced before

author: dxxp
author_rank: Newbie
timestamp: December 25, 2023, 12:03:10 am
content: One more picture is added.If you need more, please let me know.I don't understand well how the 10V ocillation is made, it will be also very helpful if you explain it briefly.

author: Swake
author_rank: Frequent Contributor
timestamp: December 25, 2023, 02:22:47 pm
content: Without schematic it would required reverse engineering to know exactly how the 10 VAC is generated. It might begin with the 2209CP as this is a voltage controlled oscillator. Then its signal is maybe buffered using the operational amplifier op470 and then send to the two FETs (there is one N-channel FET and the other is P-Channel).Are you sure the 10V output is a short? Did you remove the transformer before measuring? Asking this because I believe the 10V primary coil DC resistance of that transformer will be very low and that might be confusing. If the output without transformer connected is indeed a short you can find back what component is causing problems by tracing the short. It is frequent with SMPS power supplies that multiple semi-conductor components are blown.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 25, 2023, 03:17:41 pm
content: 2209 will be your generator going thru the 633 and use some op amp to buffer / drive the 2 mosfets as push pull drivers with the transformerthats what i think, its a very basic smps with little feedback if there is ... surely no protection of some sort, when fuses blows it's alreay too latea simple tl494 design would have been betterhave to decipher the mcu side, if its an pwm clock of some sort, or provide some functionalitywhen you dont have schematics search for datasheets and try to guess the circuit ...

author: dxxp
author_rank: Newbie
timestamp: December 31, 2023, 12:49:15 am
content: Yes I removed the transformer before measuring it.After replacing Mosfet which is irf640 and seems to be damaged, it was fixed.10V terminal isnt shorted to GND anymore.I thought this was 500Vdc power supply but actually it has AC output.Setting voltage chages input and output voltage linearly.