[Coco] off topic - to electronics guys

Gene Heskett gene.heskett at verizon.net
Sun Mar 15 22:58:38 EDT 2009


On Sunday 15 March 2009, mike delyea wrote:
>I've attempted to fix an LCD monitor I found in the garbage.  It
>exhibited the same symptoms listed here:
>
>http://www.badcaps.net/forum/showthread.php?t=2658
>
>I've removed the bad caps and replaced them according to the
>instructions listed in the above web page.
>The monitor started up and (Yea!) I had a stable image - for about 10
>seconds.  Then I noticed a whining sound
>and smelled burnt plastic.  I quickly unplugged it and examined the
>board.  The image is here:
>
>http://www3.sympatico.ca/michaeldelyea/index.html
>
>What is that part?  It has the same numbers on it as the one to the
>left.  Any ideas how to proceed?
>
It looks to be another 22pf, 3 kilovolt rated ceramic capacitor.  It may have 
been overstressed by the original failure of the capacitors.  But note 
carefully, the pcb has a slot milled through the board between the capacitors 
contacts, so they fully expected it to have to withstand 3 kilovolts. In the 
presence of a nearby lightning strike or some such.

The choke between them is a longitudinal choke, not much effect at line 
frequencies but becomes an heavy impediment to lightning induced surges that 
are common to both sides of the powerline.  Those two capacitors are likely 
from the powerline to the monitors internal ground.  The AC power for the 
monitor passes through that choke if I'm reading between the lines correctly.

I would remove the cooked one and obtain another, but before I replaced it, I 
would carefully carve away all signs of the cooked & burnt pcb.  The carbon 
will be a bypass track and could very well make the monitor dangerous to your 
health & well being from a shock.

I'd see about getting a schematic but those will be very hard to come by 
unless Sams has it covered.  If it works when you fire it up, the next thing 
I'd do is verify that it isn't leaking a potentially dangerous shock, into 
anything that's plugged into it.

I may be full of it otherwise, but that last point can't be emphasized enough.

>I've examined my solder joints with a magnifying glass and they are
>all OK (no spillage, polarity correct).
>
>--
>Coco mailing list
>Coco at maltedmedia.com
>http://five.pairlist.net/mailman/listinfo/coco


-- 
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)
You know you've been spending too much time on the computer when your
friend misdates a check, and you suggest adding a "++" to fix it.




More information about the Coco mailing list