On Tuesday, February 21, 2012 12:46:48 PM Jon Elson did opine: > gene heskett wrote: > > I believe that may be the maximum self destruction voltage, assuming > > sufficient is available to reach that. At my dvm's diode range, I > > checked 6 of them, 3 had never seen power, and they all read a couple > > of millivolts from .989 volts forward, and with nearly 21 ma now > > flowing its just a few millivolts above 1.24 volts. > > OHHHH! These are IR LEDs, which have a lower forward voltage than > visible light > LEDs. Those voltages sound right to me. > > > Working from one of those 8 ounce bags of 5 or 10 each tape bound > > 1/4th watt R's the shack has peddled for years, I spotted the 150's > > thru the bag, but when my hand came back out of the bag, it had > > 150k's in it, third strip a pale yellow. So, swapping them out, and > > they actually read 147.7 ohms this time, I now have 3.098 volts > > across the resistor in series with each LED, and the led voltage is > > showing at about 1.24volts for all 3 of them. So now I have > > 3.098/147.7= 0.0209 amps thru each one, and they switch as expected > > when the slot is blocked. > > Ah, that makes complete sense. > > > These 1 oz circuit boards aren't really made tuff enough to be > > repaired, so there is now 3 pieces of wire wrap bypassing broken > > traces > > > > > > TBT, I really need an iron with about a 1/10th sized tip & only maybe > > 10 watts for this, > > Yes, a good iron is a KEY tool! You should see the stuff I do > manually. 0805 passives and > chips down to 0.4mm lead pitch. I do a lot of work with a stereo zoom > microscope. > I use Weller EC2002 controls and the Weller EC1302B iron, although these > are getting pretty hard to find on eBay. Repair parts are expensive. > The WSL box and > WMP iron are almost as good, but insanely expensive new. > > Jon > Two things. Weller designs to make sure they have a steady market in repair parts. The first of their irons I ever had, was the original black one that used the curie point of an iron button in the back of the tip and you could buy tips in 50F increments from about 500F up. That was circa 1959, and that iron still works today although the ultra flexible and heat proof silicon cordage on the hand piece has pretty badly deteriorated. Probably close to 20,000 hours on its heater.
About the time they switched to the blue plastic housings, the heater failure rates exploded and while I have had several of them since, heater life has been in the 1000 hour category. So you either keep a couple in stock, or you bail. I used up 4 of them the first 3 years I was the CE at WDTV, and when the local parts house had the XYTronix made GC iron with a dialup temp setting, I gambled $125 of WDTV's money. It turned out to be so much better than the wellers, I bought one for myself a month later. And as the wellers upchucked, at the station, they got replaced by these. The only failure I have had was because I'm a good fellow & don't mind helping out occasionally. In upstate MI, broadcast techs, particularly those that try to keep small town radio stations on the air, are both ill equipt and poorly trained. Not to mention the station buildings are rarely up to NEC code. I wandered into one of those a few hundred feet above WDHS in Iron Mtn. MI one evening as I was leaving and there was a pickup truck with some radio service logo on the side backed up to the building, so I stopped in to talk shop, difficult when the guy was so green he didn't understand the language. Anyway, he was trying to put a 5KW collins FM back on the air after a fairly major burnup in a screen circuit of the final & I stepped up and started checking out what was still wrong, decided I needed to unsolder one end of a 5 watt film resistor to check it. He didn't even have a soldering iron! Going to my GMC I pulled old faithfull out, found a drop cord which I should have checked as both ends of a rather worn hunk of 14 ga SJ cable had Hubbel replacement plugs. Of course it was crosswired by some color blind person, so my iron was demolished the instant it touched a grounded surface. So I first unplugged the cord again, then checked the duplex which wonder of the ages was wired right, so I cut both ends of his drop cord off & reinstalled the connectors properly and went down to my transmitter & got a $20 shack iron & came back up, along with a suitable resistor in case I was right, and put him back on the air. Its amazing how fast word spreads, only the cellphone techs ignored me after that, the rest of the radio folks did a lot of bowing in subservience and all that whenever I come around since. Anybody who works with "pictures" is a god of some sort to those folks I guess. Another time & a different radio station on that same hill, the guy was trying to get it up to power and stay on the air but it kept tripping off from screen overloads. In 20 minutes his hands never went anywhere near the tuning controls, so I asked if he minded, pointing at those knobs, an easy fix because the final was drawing way too much screen current that if the tube had been glass, the screen wires could have been seen running red hot. Short story, ten minutes tuning and it was making well over its rated 5KW at about 10 mills worth of screen current. I tried to teach, but how well the student learned will be up to elapsed time to tell. It turned out he had been screwing with it for 2 weeks and 2 destroyed $3k final tubes then. I could probably move to the UP and have all the radio work I wanted in my dotage. Too cold for me and my diabetic feet on an everyday basis though. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Always look over your shoulder because everyone is watching and plotting against you. ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
