Repairing WFCO 8955 converter and closely related models
So I repaired a couple of these converters and I want to share my knowledge and I am also hoping someone with a little more understanding of these will join the discussion.
There is 2 types I know of. Type 1 does not have a daughter board. Type 2 does have the daughter board.
If your converter is not blowing the fuse and your voltage is from 2 to 7 volts then you are in luck, it is an easy fix. Those 2 rectangle white ceramic resistors is the cause of ALL your problems. They get so hot that everything around them burns up. So change all the small capacitors near the 2 white resistors.
If you have type 1 then you just need to change 1 capacitor, but when you put the new one in, place it on the underside of the board to keep it away from the heat.
If you have type 2 with the daughter board then you will have 2 or 3 capacitors to change, the 3 small capacitors closest to the white ceramic resistors. Because the KA3846 IC chip is located near the heat it may also blow. If it does blow it could literally explode your mosfets. So if your Mosfets or large diodes are blown you need to suspect the KA3846 IC.
This is where I need help from some with more knowledge of these. After replacing the KA3846 IC the unit does not work, 0.00 volts. So I could use some help.
If you reversed your polarity or crossed the wires you blew it up; but not to worry, it can still be fixed. First thing is to check the underside for broken solder connections or burn marks, those parts should be replaced. Check your mosfets and large diodes on the large heat sink to make sure they did not blow. Next is to check and replace the fuse. After that just go over the board and test whatever your skills will allow. If all is good you may have fixed it. There is a big green wafer thing that usually blows up, it protects the unit against surges, if yours is about 3/4 wide it may be a 2R515 but if it is an inch or bigger then it may be a 251R0.
I also have done upgrades to some of mine. I have added heat sinks to the BIG ceramic resistors and small fans that turn on using thermal switches.
So anything about fixing these, upgrading them, or modifying them. I am interested in what we can all learn. ALL these units will fail from the heat of those ceramic resistors.
I got a heat shield on all of mine that have the daughter board, and when possible I reinstall the capacitor on the underside of the board. :)
There is 2 types I know of. Type 1 does not have a daughter board. Type 2 does have the daughter board.
If your converter is not blowing the fuse and your voltage is from 2 to 7 volts then you are in luck, it is an easy fix. Those 2 rectangle white ceramic resistors is the cause of ALL your problems. They get so hot that everything around them burns up. So change all the small capacitors near the 2 white resistors.
If you have type 1 then you just need to change 1 capacitor, but when you put the new one in, place it on the underside of the board to keep it away from the heat.
If you have type 2 with the daughter board then you will have 2 or 3 capacitors to change, the 3 small capacitors closest to the white ceramic resistors. Because the KA3846 IC chip is located near the heat it may also blow. If it does blow it could literally explode your mosfets. So if your Mosfets or large diodes are blown you need to suspect the KA3846 IC.
This is where I need help from some with more knowledge of these. After replacing the KA3846 IC the unit does not work, 0.00 volts. So I could use some help.
If you reversed your polarity or crossed the wires you blew it up; but not to worry, it can still be fixed. First thing is to check the underside for broken solder connections or burn marks, those parts should be replaced. Check your mosfets and large diodes on the large heat sink to make sure they did not blow. Next is to check and replace the fuse. After that just go over the board and test whatever your skills will allow. If all is good you may have fixed it. There is a big green wafer thing that usually blows up, it protects the unit against surges, if yours is about 3/4 wide it may be a 2R515 but if it is an inch or bigger then it may be a 251R0.
I also have done upgrades to some of mine. I have added heat sinks to the BIG ceramic resistors and small fans that turn on using thermal switches.
So anything about fixing these, upgrading them, or modifying them. I am interested in what we can all learn. ALL these units will fail from the heat of those ceramic resistors.
I got a heat shield on all of mine that have the daughter board, and when possible I reinstall the capacitor on the underside of the board. :)
