ms2240 cap info

[ttocs]

ok I got the board out. thanks for the advice on the fets it made them easy. There is one spot on the insulating pad that looks like it made contact but it doesn't look to have been hard enough to go through. There is evidence on the heatsink that someone used a screw driver to pry the fets off of the sink. What do I test next/how? Check the fet pins for shorts now?

[trickyricky]

Yes check the fets for shorts, if one of them has a short on all between all three pins then go ahead and remove it and retest the remaining fets. There is also a large diode that is in parallel to the B+ and ground right near the transformer, remove from circuit and test as well to see if current flows both ways (if so then it's no good).

[ttocs]

ok q9 is still showing a short between all 3 and the others are still showing as short between 2 legs. I will pull it out and retest as well as the diode shortly.

[Eric D]

Be very careful when you remove those parts. If you overheat the solder pad, it will fall right off the board. This will make the rest of your work much harder.

To remove those parts, I typically add more solder, and quickly jump from pin to pin with my iron until all three pins are hot enough for the part to drop out. I then use a solder sucker to clean off most of the solder, and follow up with solder wick.

[ttocs]

I have desoldering iron with the sucker ball attached that I use. Good/bad for this?

[Eric D]

Good for removing the solder AFTER you remove the part. BAD for removing the part itself.

Any method involving removing the solder, then removing the part typically results in damaging the vias in the board. The tiny bit of solder still in the hole will still bond the part to the via.

Sometimes the via is much larger than the part's pin, in this case you can suck solder out and the part will then fall free, but I seldom notice these cases.

[ttocs]

ok I took out q9 and when it was out it doesn't show a short on any of the pins now. But then D9 showed a short on all 3 so I took it out and it still read a short on all 3 after. All the rest still show a short between the same 2 pins they did before.

[trickyricky]

If D9 has current flow both ways (test leads flipped) then it's bad.

By same two pins you are talking about the middle pin and the one on the right (3rd pin)?

Also did you check the diode that was near the transformer?

[ttocs]

yes the middle and the 3rd leg still show they are shorted. I started to take out the diode but I will need some desoldering wick to get it off my desoldering iron can't get it.

[trickyricky]

You might as well then remove all the mosfets, and test the bridge rectifier diodes (two devices attached to the sink, next to the fets). If the rectifier diodes are shorted then those devices will have to be replaced as well as the mosfets and perhaps the protection diode.

[ttocs]

so the search for parts begins