About 3 weeks ago, I was blessed by the addition of a Samsung
Syncmaster 243T 24" 1920x1200 LCD monitor to my repair backlog. It
had been sitting around the donors office for a year or two, so nobody
could recall why it was retired. I plug it in and it appears that
everything is working. I have two similar LCD monitors at home for
running my flight simulator. A third monitor would make a start on a
wrap around cockpit window view. (actually 4 is about right).
So, I take home the monitor, being careful not to bash in the screen
like I did the last monitor I took home by planting the groceries dead
center in the middle of the panel. It arrive safely, I plug it in,
and nothing works. No power, no pilot light, no messages, no nothing.
I'm not exactly equipped at home to fix monitors, so I drag it back to
the office where it sat around for a few days. I plug it, and
everything works normally. I check for intermittents by beating on
the monitor, but nothing happens.
At this point, a sane and rational person would tear the monitor
apart, look for problems, probe around with a volts-guesser, determine
the culprit, and fix it. Nope. I'm out of bench space and have no
room to work on a big monitor. So, I drag the monitor home again, and
once again, it's dead on arrival. So, I drag it back to the office
for the 3rd time, where it once again works perfectly.
This would be a good time to guess the cause (although I haven't
really revealed enough info to make a proper deduction).
I still haven't ripped it apart to see what's going on, but I do have
a good guess what's wrong. It probably has the usual bulging
capacitor problem in the power supply. I keep the office at 72F (22C)
to keep the customers happy. At home, I prefer something around 65F
(18C). The workbench, where I do my testing is not very well heated,
and is probably colder. Outside temperature is now about 43F (6C).
Bulging electrolytics are detected by measuring the ESR, which
increases as they leak. Heating the caps lowers the ESR back down.
Cooling the caps raises the ESR back up. Incidentally, this is why
some devices run merrily when warm, but won't turn on when allowed to
cool off. The Samsung monitor is likely teetering between working
when warm, and not running when cold.
I'll disclose what was really wrong after I fix it, probably next
year.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558