On 1/17/2011 9:18 AM, The Daring Dufas wrote:
On 1/17/2011 7:46 AM, Jeff Thies wrote:
On 1/17/2011 5:06 AM, The Daring Dufas wrote:
On 1/16/2011 10:25 PM, Tony Miklos wrote:
On 1/16/2011 9:18 PM, PE wrote:
Hi all: My 15-yr old Toshiba 27" crt television has recently
developed a
problem which is that approx 15 minutes after being turned on, the
picture
bows inward on the left and right sides. Then, after a few more
minutes,
the picture resolves and returns to normal and remains perfect for the
remaining time the tv is on. If the symptom described above means the
crt
is wearing out, so be it, the set will soon be history. However, I'm
wondering whether some other, replaceable part, might be going bad and
causing the temporarily distorted picture.

Would appreciate any suggestions re. probable cause(s) of symptom
described
above. Am basically novice, but handy and with soldering skills, and
have
done a few simple tv repairs in the past. Thanks for your replies!


I'll bet it is a bad capacitor, fixed hundreds of video game monitors
with similar symptoms. Most of the time we don't even test the caps,
look for parts of the circuit board that look like they run hot, then
replace all caps in that area. Also replace all caps rated for 100
volts
or higher, they go bad much more often. Also if you know your way
around
a monitor, be sure to change the caps in the vertical and horizontal
circuitry. For newbies in the video game monitor repairs, lot's of
people put together a list of all the common caps that fail on that
particular model and sell you a bag of caps and a picture showing what
goes where. The "cap kits" will fix several problems at once, including
problems you didn't notice yet but are about to go.

Actually my TV is doing the same as yours but it stays that way.
When it
quits I'll probably take a look inside, but chances are I'll toss it
and
get a new one instead of fixing mine. TV's have a lot more components
than cheap video game monitors and aren't as easy to fix (not for me
anyway).

OH, no way is that a sign of a bad CRT, and no way is the yoke itself
bad, just the circuitry that powers the yoke.

You beat me to the bad capacitors. 15 years is a darn good life for
consumer grade electrolytic capacitors. I had a customer who's Viewsonic
LCD monitor on his server/office computer died after a year.
I thought it a shame to toss a nice monitor so a little Google search
turned up a common problem with an electrolytic in the power circuit
on the main circuit board.

Google might work. I fixed a couple of DTV converter boxes by googling
the problem and found a cap that failed in all of them. Likewise
replacing caps is a common problem in switching supplies (Mac supplies
in particular) although that is not the issue here. Claire is close to
having this nailed, the symptoms are almost classic.

Capacitors have gotten a lot smaller for the same ratings, I suppose
it's not to be unexpected that they would fail more often. The digital
stuff in particular as switching supplies are hard on them.

Not sure how long modern HV sections hold a charge, but some caution
should be exercised.

Jeff


I just reread his post and I've seen the same symptoms caused by cold
solder joints.

It's the bowing part that lead me to think cap, but you are right that
healing like that is not really a cap thing. I've got a friend who still
fixes TVs, though mostly it's all flat panel stuff now. I'll ask if I
get a chance...

After a warm up the device starts working correctly but
it will GRONK if you jar or slap it hard. I used to repair a lot of two
way radio gear and when I finished repairing a problem, I would smack
the unit against my carpet covered work bench much to the consternation
of the other techs in the shop. I explained to them that the radio was
going to get a lot rougher treatment in the field.


It's better to know sooner than later. Toward the end of my repair
"career" I was mostly fixing giant car amps. Nothing I could do to them
could come close to the abuse they would get later! Oh, the abuse!


I've also seen a lot
of very strange thermal intermittent malfunctions.

I've used more than my share of freon tracking them down. Or not
tracking them down!

Jeff



TDD