On Tuesday, February 10, 2015 01:29:22 PM Dave Cole wrote: > What would be burning up those diodes? > > Incorrect wiring to the drive? > Leaking electrolytics? > > In my limited experience, diodes usually don't fail for no reason. > > Dave
Bad capacitors are usually the culprit. A capacitor with a high ESR (even as low as 1 ohm can be very important in these circuits) can sit there and look perfectly innocent, but the voltage spikes it is supposed to absorb are busy blowing everything around it. It may show up as a warm spot via your IR thermometer if you survey the operating circuit with it before the cap fails open. If its even 10F above the surrounding parts, it is on its way to the graveyard, replace it as preventative maintenance. Since a decent ESR meter is both rare unless you're really in that business, and around $200, its generally cheaper to just replace the suspect caps. FWIW, 99% of the digital meters that purport to measure capacitance operate at such a low measurement rate that they will ignore the 10 ohms of internal resistance the cap might have and proceed to tell you with a straight face that the 220 u-f cap you are looking at with the probes is still showing 334 u-f. The + tolerance is quite high on that stuff. True ESR measurements are usually made using a 100 kilohertz excitation signal at voltages too low to turn on any surrounding semi's in the circuit, so the measurement is made in-circuit and be more valid than what you get after applying the desoldering heat to remove it. > On 2/10/2015 12:53 PM, Jon Elson wrote: > > On 02/09/2015 10:43 PM, Dean Posekany wrote: > >> After the comments/recommendations to think about attempting a > >> repair to the Parker drives, I popped several open and took a good > >> look around. On the top surface I could find no obvious problems. > >> Not popped caps, no burn marks, nothing. On the bottom, I found > >> what looks to be a problem on two of the bad drives. There are > >> three SMD's located near the drive output port that appear to be > >> toast. The problem is I can't identify them. The board stencil > >> “CR†notation seems to indicate they are crystal rectifiers and > >> you can see polarity marks on one side. I tried to track down the > >> SMD codes online but had no success. Soooooooo, since some of you > >> spurred me on, I thought I'd throw this back out here to see if any > >> of you guys had any ideas. I've attached links to three photos that > >> may be of some help. > >> > >> This is a close-up of one of my good drives: > >> > >> _https://www.dropbox.com/sc/fzugl3ebp7hlbbj/AABZSMn6f70FORZS3FpRhRc- > >> a_ > > > > The markings appear to be CU02 then on next line M ON. > > The CU02M shows up as a CMR1U-02M, available from Digi-Key. > > 200V 1A, 35ns reverse recovery time. > > > > > > Jon > > > > --------------------------------------------------------------------- > > --------- 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 > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > --- > This email has been checked for viruses by Avast antivirus software. > http://www.avast.com > > > ----------------------------------------------------------------------- > ------- 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 > [email protected] > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
