Meanwell SP-500-12 PSU - Page 1
Forum section: electronics / repair

author: RyanG
author_rank: Regular Contributor
timestamp: May 08, 2017, 10:31:40 pm
content: Someone asked me to look at this power supply. It's a 12V 40A supply. They only told me that it didn't work. I changed out the fuse in it, which is 10A. After I did that I plugged in just the input board and the FET in the picture marked with the blue dot shot flames out the side instantly. I changed out that FET, and replaced with another of the same, IRFP460. The replacement did the exact same thing. I don't see anything burned or broken on the entire board. I do think that someone dripped oil onto the output board, but the input board doesn't work even without the output board attached.

author: RyanG
author_rank: Regular Contributor
timestamp: May 09, 2017, 07:54:01 am
content: I have been working on this, slowly taking the components out of circuit and checking them. I took a triac off, and it had continuity A2 -> A1 but not A1 -> A2. I'm assuming that it's bad because it shouldn't have continuity in either direction. If anyone has any ideas other than that it would be appreciated. The triac is on the horizontal heatsink with the diode bridge.

author: oldway
author_rank: Super Contributor
timestamp: May 09, 2017, 11:33:19 am
content: I found on Internet that this is a power supply with PFC.What is the triac used for ?We find sometimes a triac in power supplies without PFC to switch input voltage 110/220V automaticaly.When the FET blows up, there is generaly more damaged components, mostly the controller IC.Repairing SMPS is dangerous, be very careful.It seems that you have no experience in such repair....it is already very difficult for an expert to repair such a SMPS without schematics....You will have to do some "reverse engineering" first.

author: bktemp
author_rank: Super Contributor
timestamp: May 09, 2017, 11:56:59 am
content: Looks like the PFC mosfet. Check the diode (the other device on that heatsink).A triac in a power supply with PFC is unusual, because 110/220V switching isn't necessary because of the PFC boost stage.Are you sure it is a triac and not a mosfet or diode?

author: RyanG
author_rank: Regular Contributor
timestamp: May 09, 2017, 05:38:45 pm
content: It is a BTA16-600B. I know that these aren't easy to repair and I already gave myself a good shock on my nose from the heatsink attached to the 2 FETs. The drain of the FET that blew up comes from the diode attached to the heatsink at the bottom left, which comes is connected to the + side of the 400v caps. The source of the FET connects to the - side of the 400v caps. The 2 FETs on the shared heatsink have connected drains and sources. I have checked every other large component on the board, and the triac is the only one that tests bad. I haven't checked the smaller transistors and other stuff at the top left in the picture.

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 09, 2017, 05:46:46 pm
content: Quote from: RyanG on May 09, 2017, 05:38:45 pmThe trial I think ils only protection.I don't think he is bad.look control IC,chemical capacitors.until the PS starts working put a load like 100w light bulb in series with power mosfet.Bon courageEnvoyé de mon iPad en utilisant Tapatalk

author: RyanG
author_rank: Regular Contributor
timestamp: May 09, 2017, 06:46:24 pm
content: The big resistor standing in front of the triac was also bad. Tested with DMM as an open circuit. The triac looks like it goes from all the input circuitry at the bottom right to the diode bridge.

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 09, 2017, 08:37:07 pm
content: Quote from: RyanG on May 09, 2017, 06:46:24 pmPut on papier the triac schematics to see if it's protection or power factor regulation.the fuse blowing ils not consistent with 'blown' resistor.you need to dig deeper...Regards,OvidiuEnvoyé de mon iPad en utilisant Tapatalk

author: oldway
author_rank: Super Contributor
timestamp: May 09, 2017, 08:43:05 pm
content: I think that "the big resistor" and the triac are the inrush current limitation circuit during power on.PFC does not works with 100W bulb in serie...This works only for SMPS WITHOUT PFC.

author: RyanG
author_rank: Regular Contributor
timestamp: May 10, 2017, 03:07:39 am
content: I forgot to mention that after I put the new FET on the board along with a new fuse the FET blew up and the fuse never blew.

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 10, 2017, 05:34:03 am
content: Quote from: oldway on May 09, 2017, 08:43:05 pmI don't agree... I started smps's with series bulb several times, even it doesn't start fully you see on scope the IC switches, that's all you need to know and remove the bulb WITHOUT killing the Mosfet. Have you really tried and put a scope on gate or drain?If the triac is slow start just take his circuit out, also if he is protection I suggest take it's role off and as first step verify if control IC switches by protecting the Mosfet.You really don't care of protection if control mechanism is bad.Regards, OvidiuEnvoyé de mon HUAWEI NXT-L29 en utilisant Tapatalk

author: RyanG
author_rank: Regular Contributor
timestamp: May 10, 2017, 06:19:59 am
content: Here is a picture of the second board that is part of this supply. The ICs on this board are the TL3845P PWM controller, HPC3022 Bi-directional Photo-Thyristor Output Optocoupler, 2 PC123 Optos, 2 MOSFETS on the left hand heatsink, and 3 SBL3060PT Schottky Barrier Diodes. I'm thinking this board is required for the whole thing to work correctly especially since one of the sets of wires goes from right next to the PWM controller over to the low voltage area of the other board. Don't really know why I didn't test it all together after changing the stuff out. It was given to me separated. The second picture is of the connectors/jumpers on the back of the supply(upside down so I didn't have to screw it all together). Wouldn't I need a jumper connecting the -V to the -S for this to work? Thanks for the help.

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 10, 2017, 06:34:20 am
content: I don.t think jumper is needed,you have allready on/off on the upper side.3845 si the most solid pwm chip I know but sometimes it burns.disconnect 3845 output from mosfet and put a scope on the output,normally the ic is powered on but verify also chippower something like 12-14 v .You can't repair this without at least a schematic of 3845 configuration you really need to draw a part on schema or use the 3842 typical config with respect to stand-by used on your sch (that's for you to identify on the board)Regards,OvidiuEnvoyé de mon iPad en utilisant Tapatalk

author: albert22
author_rank: Regular Contributor
timestamp: May 10, 2017, 07:38:30 pm
content: QuoteI have seen this inrush current circuit on certain power supplies. I dont think that would be necessary if the power supply does active pfc.

author: RyanG
author_rank: Regular Contributor
timestamp: May 10, 2017, 09:27:19 pm
content: I put a new triac and resistor in there anyways and it burned the resistor instantly.

author: RyanG
author_rank: Regular Contributor
timestamp: May 11, 2017, 03:57:06 am
content: I'm thinking the garbage can is the best place for this thing. Well, after I take off the good parts.

author: oldway
author_rank: Super Contributor
timestamp: May 11, 2017, 05:07:15 am
content: Board 1 is the PFC and board 2 is the converter.You must also replace the controller of board one, not only the FET.The resistance burnt instantly because there is a short circuit in the HV circuit. (HV must be between 380 and 400V when PFC is working).The HV electrolytic capacitors are precharged by this resistance and the triac bypass the resistance when HV has reached a sufficient voltage.Repairing SMPS is dangerous and it is not for a beginners in the field of power electronics.You better stop with this and ask for help with somebody who knows how a SMPS works.

author: Rasz
author_rank: Super Contributor
timestamp: May 11, 2017, 03:33:55 pm
content: Quote from: RyanG on May 11, 2017, 03:57:06 amnah, it needed troubleshooting, not replacing random parts and hoping it wont blow up