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 Post subject: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 5:19 pm 
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Im not sure how I did this but, but after the recap, I was changing out the selenium rectifier with a Silicone 1N4007.
While Powering it up on the variac it did draw a little high but not over 800ma.
Then my new value diode resistor started smoking.. well after an hour of checking my work (caps, resistors) I finally noticed I put the diode in backwards… GREAT.. I clip it out and replace it again.. Well the same thing happen… scratching my head and an about 30 min later.. I discovered I did it again.. the diode is in backwards for the second time… It now works great… Happy but a little disappointed in myself.
BTW, I did and do know about the markings being differant on a selenium.

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 6:01 pm 
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I've done that with caps. Not once, but twice also. I just gotta laugh at myself

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 6:37 pm 
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IMHO, it's better to use Silicon diodes---the rectification efficiency is far higher than with Silicone......

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 7:13 pm 
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Scott, I have done the same thing and made the same mistake twice over. I'm pretty good at giving myself a Mulligan when I make a mistake. But when I do it twice I have to admit I get pretty cross. But then I get over it because I've known I'm an idiot for a really long time. :lol:


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 7:33 pm 
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pixellany wrote:
IMHO, it's better to use Silicon diodes---the rectification efficiency is far higher than with Silicone......

.
But Mark, Silicone is slippery. so wouldnt the electrons move easier and faster? :D :D
.
yep should read silicon..

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If you can't explain it simply, you don't understand it well enough
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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 7:59 pm 
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Location: Melbourne, Florida
Silicon for rectification, silicone for inflation.

RRM


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 10:46 pm 
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Location: N. Palm Bch, Fl.
I replaced a selenium rectifier with a diode. Brought it up slowly and had negative voltage everywhere. Never smoked because I kept the voltage real low. I spent the rest of the day going over everything that I could think of. Even brought out the VTVM. I was somewhat new then. I came here at 5PM with a HELP. Next morning the first response was. (You put the diode in backwards.) Luckily some said they had done it also. That helped a little, but I still felt stupid.

Freeman


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Tue 14, 2021 11:22 pm 
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I have trouble many times of my Multimeter probes being reversed. And I started 1967 I think. :oops:

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 2:38 am 
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Joined: Dec Mon 23, 2019 5:52 pm
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Had the negative voltage issue also, but, it turned out the new diode was actually banded backwards !


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 3:05 am 
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Some time back while measuring current in a 9v radio, the probe on my Fluke multimeter slipped and shorted against the other battery terminal, instantly blowing out the fuse in the meter. That wasn't fun taking apart to replace the expensive fuse. :cry: :(


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 4:21 am 
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Joined: Nov Fri 10, 2006 12:24 am
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Location: Thornhill, Ontario, Canada
Every time I use a 1N4007 I still have to check to confirm anode and cathode!
So, the white band is... just a minute (checks inside cover of lab book)... Ah, Ha...cathode!
Cheers,
Roger.

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 3:30 pm 
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Back in the 70s, I assembled a Heathkit IG-28 Color Bar Generator. On first power up, it blew the fuse. So, I replaced the fuse again. Blew! It took me a while but I finally found the culprit. Believe it or not, it was not an error on my part. The silicon diodes were banded on the wrong end. At the time, I didn't have any more of those early epoxy rectifiers so I just turned them around in the circuit until I got new ones. That was a head scratcher.

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 3:48 pm 
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I have done this WAYYYYYYY too many times. So much so that I seriously have a schematic taped to the wall next to my bench so I can make sure I have the diode facing the wrong way, only to get it backwards anyway.


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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 11:19 pm 
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WOW, Its the first I ever heard of the diode marked wrong.. Im not sure I would have figured the problem out.

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If you can't explain it simply, you don't understand it well enough
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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Wed 15, 2021 11:28 pm 
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sawblade54 wrote:
WOW, Its the first I ever heard of the diode marked wrong.. Im not sure I would have figured the problem out.

Scott, on a whim, I tried an analog VOM test on it. That confirmed the backwards marking. I wonder how many other ones Heath had to deal with?

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Fri 17, 2021 1:21 am 
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I once inspected a lot of assembled PCBs that all had some caps installed backwards. The boards were perfect and every one of them was identical. This came to light during installation in the finished products on power up and I got a good lesson as a young inspector. I have seen it in other stuff. I received a small circuit card from a major aerospace company once. To install as a replacement in a unit. This board cost the company 4000 dollars as I recall. Did not look like 4000 worth at all. But it had a yellow inspection tag and approval with the stamps of multiple inspectors and testers all over it. I put it in the unit and began to test. I think something burned up right away. A component was installed incorrectly and there was no way it was ever tested or powered up. My boss said fix it, we would not bother to pursue a warranty claim of any sort. I would have, 50$ worth of parts on it at best.

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 Post subject: Re: Same Mistake, Same Mistake
PostPosted: Sep Fri 17, 2021 5:13 pm 
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It's possible that the new caps may have been damaged by the reverse voltage, maybe shorten their lifespan.


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