Monitor degauss problem
FJose
Let me start this message with a comment about myself: I hate to see
valuable devices (i.e. electronic junk) being trashed without reason.
Some years ago, B&W TVs were massively trashed. Now, computers are.
I think it is a pity to see how 'obsolete' (by today standards) parts
are just discarded, being still useful items.
Well, some days ago I run across a 14" monitor which my neighbour had
just trashed and was left in the street waiting for the dumpster.
Being as I am, I just could not resist to take it home and look for
the reason for its sad destiny.
Preliminary inspection revealed some cosmetic damage in a corner, but
nothing which some work could not restore, if needed. So I hooked it
to my PC and powered it. It came to life. Someway. Because it had
basically three zones: upper left corner was a big green one, upper
right was purple and lower half was almost right. But I got surprised
to find that it was woking fine at 1024x768, 75Hz. Not bad for a 14"
unknown brand monitor. And picture was crisp enough to guarantee a
good (useable) one at 800x600. So I decided it was a keeper ;-)
It seemed to me trouble was in the degauss circuitry so I opened the
case and looked at that circuit. It has the usual arrangement of a
PTC cube (Sincera brand). I measured the degauss coil and it was not
opened. Checking the PTC in cold condition I got about 12 Ohm for
the larger element (in series with the coil) and about 200 Ohm for
the heater element. When powered, PTC gets pretty hot but I think the
degauss circuit does not operate.
And here come my questions:
*Are the PTC cold resistance values good?
*How much time should the degaussing coil be activated?
*Should I use the same PTC type or is there a generic substitute
available?
Any other hint appreciated.
Thanks!
JOSE
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73 EB5AGV / EC5AAU - JOSE V. GAVILA
La Canyada - Valencia (SPAIN)
EB5AGV Vintage Radio Site: http://www.geocities.com/eb5agv
European Boatanchors List: http://groups.yahoo.com/group/euro_ba_swap
Jerry Greenberg
Usualy these degausing thermos go opened or shorted. When shorted, they
usualy cause the main AC fuse to blow. If you know the specs, you can
compare it to some of the other manufactures and replace it with anything
that will work. For the 3 pin type, I've used the ones from of of the
Sony sets. (We do a lot of Sony).
The degausing coil is active for about 100 to 200ms on the average. In
the larger sets, it sounds like a sudden buzz noise for a split of a
second. The smaller ones may be too low to hear. You can tell if it is
working by putting an AC Volt meter accross the coil. Set the meter for
120 VAC range. Turn the set on from cold. The meter should jump up, and
then have a rapid decay. Because of the bullistics or speed of the meter
responce it may not go to the full 120 VAC, unless it has a high speed
capture option. But you will see the effect.
You can also put a small 120 VAC lamp accross the coil. It will flash when
the activation occures. Use not more than about 5 to 10 watts. Don't put a
40 or 60 watt lamp accross the coil. If you do, you may be changing the
thermo resistor afterwords.
--
Jerry Greenberg GLG Technologies GLG
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