On Tuesday, February 10, 2015 10:01:13 AM Dean Posekany wrote: > On 2/10/2015 3:00 AM, Gene Heskett wrote: > > snip > > > The diode checker of the modern meter reads the voltage drop, fwd > > direction on this type of diode s/b under .15 volts, while the > > reverse of the probes should show a much higher voltage, maybe even > > off-scale for reverse. Right where they sit in circuit. A reading in > > both directions that is similar and probably under .1 volts is a > > shorted one. > > I checked the three diodes on the bottom near output port and they all > read generally the same: forward bias ~0.48V and reverse bias ~1.47V. > I checked a few of the topside diodes of the same value and got: > forward bias ~0.48V and reverse bias .OL. It appears that the bottom > diodes are bad. > > Is there any way to check the FET's. These are going to be a PIA to do > a wholesale replacement due to the way they're mounted to the heatsink. > It looks easy, but with the spring clamps and the age on the heatsink > compound, they're locked in there pretty well. > That I would approach from a "first remove the heatsink" angle. The spring clips s/b removeable, then once its suitably loose, a razor blade at a low enough angle so as not to dig into the heat sink can probably pop the individual FET's off the sink. Once the sink is out of the way, and the needed soldering tools are on hand, then the rest of it is applying the short to all the legs and sucking the solder out of the holes with a vacuum sucker. Be aware that those big blue sucker tools with the white nylon tips are NOT anti-satic. I have both styles but the larger blue original, while doing a better job than the smaller orange versions, also have enough recoil that they can damage the hot pcb. The smaller one is quite a bit gentler in that regard.
Then clean the heat sink off with whatever solvent seems to work, and apply a small amount of something like Artic Silver to the FET's cooling faces, doesn't take a lot (a bookmatch head sized drop is a great plenty) as the spring clips will extrude it out to fill the voids when they are re-installed. Once the new ones are soldered in, then you can remove the wire shorting its legs. Easier done before puttig the heat sink back on. > > ----------------------------------------------------------------------- > ------- Dive into the World of Parallel Programming. The Go Parallel > Website, sponsored by Intel and developed in partnership with Slashdot > Media, is your hub for all things parallel software development, from > weekly thought leadership blogs to news, videos, case studies, > tutorials and more. Take a look and join the conversation now. > http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
