[Coco] Died from old age?

Mon Dec 22 14:59:51 EST 2014

The coco's are so simple that is actually fun finding these problems ;)

Luis Felipe Antoniosi


On Mon, Dec 22, 2014 at 2:57 PM, Zippster <zippster278 at gmail.com> wrote:
>
> Good to hear another machine has been brought back to life.  :)
>
> - Ed
>
>
> > On Dec 22, 2014, at 1:49 PM, Chad H <chadbh74 at hotmail.com> wrote:
> >
> > My ESR meter is home-built, arduino based. I've tried testing caps or
> resistors inline before and then removing them and got different results so
> I just got in the habit of removing the part.  I pulled 2 caps this
> afternoon and tested them.  The microfarads was close to the labeled
> capacitance and the ESR was .24 on the first one.  The 2nd I pulled was the
> big 6.3v 4700uf cap.  The microfarads read ok but the ESR reading was a "?"
> so I was suspect of that one.  I didn't have any spare caps that large
> laying around but I did have a couple of old 63v 2200uf caps I had pulled
> from a old stereo receiver that were OK.  I installed one of those and the
> CoCo came alive! Yay!  I tested the original 4700uf cap afterwards and the
> ESR reading was "0".  From my experience with capacitors, the ESR on good
> capacitors seems to be slightly more elevated as the microfarads
> increases.  I know lower is better but "0"?  Still suspect of that, but I
> reinstalled it and the CoCo came on??  Repowered it several times and have
> been leaving it running, so far so good.
> >
> > At this point I think my problem is one of 2 things..
> >
> > 1)  Poor solder joint at one of the capacitors which re-soldering
> corrected (though I didn't notice any breaks under my magnifying lamp.)
> >
> > 2)  The 4700uf Capacitor is 'Marginal' at best and should be replaced.
> >
> > I think I'm going to order a replacement for the 4700uf capacitor and
> compare the readings from the old one with the new one, then replace it.
> >
> > Thanks for the ideas guys!
> >
> > -----Original Message-----
> > From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Gene
> Heskett
> > Sent: Monday, December 22, 2014 11:42 AM
> > To: coco at maltedmedia.com
> > Subject: Re: [Coco] Fwd: Re: Died from old age?
> >
> > On Monday 22 December 2014 11:35:56 Chad H did opine And Gene did reply:
> >> -------- Original Message --------
> >> From: Chad H <chadbh74 at hotmail.com>
> >> Sent: Monday, December 22, 2014 10:34 AM
> >> To: ooogalapasooo at aol.com
> >> Subject: Re: [Coco] Died from old age?
> >>
> >> Well I have a ESR meter so I shouldn't have any problem pulling
> >> capacitors and testing them.
> >
> > Why should you have to pull them?  The only ESR meter I have any
> experience with uses only 85 mv of AC voltage at 100 khz to make its
> measurement with.  This is so low that it does not turn on any parallel
> semiconductors it may be attached to circuit wise, so the caps are checked
> while still in circuit. Because of its time and part saving measurement
> ability when measuring surface mounted caps in DVC-PRO broadcast VCR's, it
> saved me at least 2/3rds of the time to repair and put back in service for
> many of the electronics bits & pieces of a busy TV station for several
> years.
> >
> > Its called a Capacitor Wizard, and sells for about 2 bills, made in
> Omaha originally but I think the guy has moved to KC sometime it the last
> 20 years.  FWIW, caps suffering from ESR are often easily, but temporarily
> fixed, by giving them a charge or discharge at a high enough rate to form a
> micro-weld across the ESR causing aluminum oxide at the internal to
> external terminal connection points.  Quite a few of the other so called
> ESR testers do use enough voltage to "heal the cap", for a day or so.
> >
> > IMNSHO, this particular device is the only one that measures them all,
> and does it accurately and in circuit. ANYTHING else just wastes your time
> lying to you.
> >
> > Expensive enough at $200 or so that I do not personally own one, but I
> know where one is that I can use anytime I need it.
> >
> >> I just don't know about the DIP
> >> switches.  I also need to identify the thing underneath the crazy heat
> >> sink.  I think its some sort of power transistor.  Here are pics of
> >> the board ... tinyurl.com/ko5dxy7.   Still looking for a service
> >> manual for this model.
> >
> > That is a more or less std Si, NPN power transistor in a TO-3 case.
> Never had one fail, but a strong magnifying glass may disclose a
> micro-crack in the solder around the pins on the bottom of the board.  Its
> cheap solder, so suck it or solder-wick it off & replace it with decent,
> modern silver bearing solder.  Use a temp controlled iron, needs 700F to
> remove that junk, but only about 625F to 650F for modern silver bearing
> solders.
> > Rosin core of course.
> >
> > Lead free solders need more heat. 750F maybe. But I haven't used any of
> that roll I bought with a new soldering iron 2 years ago, and now the iron
> has failed & no help from the american dealer in Lincoln NE, its out of
> warranty and I feel screwed $200 worth.  But guess what? I have a 54 year
> old weller WTC that I pulled off the shelf, and it still works perfectly at
> whatever temp is stamped on the button on the back end of the tip.  Old
> faithful.  Newer ones aren't so good, with fairly rapid heater failures
> when subjected to on in the morning, off whenever the bench lights go off
> for the night duties.  That one worked under such conditions at KOTA-TV for
> several years, and is my emergency goto iron.
> >
> >
> > 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
> >
> > --
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> > Coco at maltedmedia.com
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> >
> >
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>
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