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possible problem with Sony flat-face WEGA

I'm posting this to see if anyone /knows/ the answer, or has a reasonable suspicion. I do not want to initiate an interminable chain of speculation.

I own a 36" flat-face 400-series Sony WEGA IDTV and, yes, I have the service manual. The set has gotten heavy use over the past decade; I often leave it on when I go to bed. It wasn't cheap, and I'd like to get at least another five years out of it. For a non-HD CRT set, it has an excellent picture, especially with RGB signals from a DVD player.

When the set's turned on, the HV is apparently shut off, so that the CRT heater has time to come to full temperature, to avoid stripping the cathode. (This is speculation.) Though sound comes on almost immediately, it takes about 10 seconds for the raster to appear.

Recently I've noticed "something new". For about two seconds after the raster comes on, the black level is too light. You can see the image "darkening" as the black level drops to its "correct" point. This occurs only when the set is "cold"; cycling the power doesn't cause this.

I'm hoping someone will say "I've seen this. It's the ___________." Troubleshooting this set won't be easy (if only because it's close to the wall on a near-immovable stand). I don't want to tear into it until I'm reasonably certain I can fix it on the first try.

Thanks in advance.

--
"We already know the answers -- we just haven't asked the right
questions." -- Edwin Land
Reply to
William Sommerwerck
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Is that the same set you kept trying to give away on rec.antique.radio+phono?

Jeff

Reply to
Jeffrey Angus

Are you kidding? That was an NAD MR-20A with a failing focus system.

It is a classic set, and worth restoring -- if you can find the parts needed (most likely a no-longer-available HOT system). If someone wants it, it's theirs for the cost of shipping.

Reply to
William Sommerwerck

Wait until it is a problem that doesn't go away after 2 seconds.

--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

In other words, wait until an "intermittent" becomes permanent.

Definitely common sense -- but I'd rather make an end run around the problem.

Reply to
William Sommerwerck

Good luck.

--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

William, the condition is usually caused by the crt cathode emission becoming weaker. When the picture no longer comes on, adjusting the screen control higher will allow the set to work for a few months to a year more. Chuck

Reply to
Chuck

I kinda expected that. If you're correct, it looks like I won't get my money's worth out of the set.

I wonder if anyone still makes CRT heater boosters. Remember those?

Reply to
William Sommerwerck

If they use DC on the fliament check for a bad electrolyytic in it's power supply. I used to add a filamnet transformer to series string TV sets with a dropping diode to power an 84 volt string of filaments. They barely lasted a year from new, without the modification.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.
Reply to
Michael A. Terrell

Well, this set's over 10 years old. I'll pull out the service manual and give it a look.

Reply to
William Sommerwerck

CRT brighteners are still available but I wouldn't go that route until the screen control adjustment is no longer effective.

Reply to
Chuck

.

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de.

The industrial Sony's do a very similar thing as the CRT warms up. In those you're waiting for the beam current feedback to get up to speed. Since you have the service manual, is there anything in there about setting G2 by monitoring a specific set of lines in the vertical interval?

G=B2

Reply to
stratus46

I don't know; I haven't looked yet.

Is there any way to do that without reducing vertical scan?

Reply to
William Sommerwerck

Once you need a filament booster it's time to get the good old Sencore CR70 'Beam Builder' out of storage.

Or maybe just a bottle of Jim Beam?

--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

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