Philips CRT TV: white lines and green flashes

I have a Philips 30" HD CRT (30PW850H37A), manufactured July of 2003. Though it's an old TV, I love everything about it: The virtually-zero display lag, beautiful contrasting colors, and fast response times. I actually haven't owned this thing very long, I picked it up at Goodwill just last week for $28.

However it's problems are now starting to show. At first it was just stagnant white lines zigzagging from the bottom to the top of the display. I knew this before I bought it and thought nothing of it because when I turned it to the blue-screen background, the lines were basically invisible. The lines do show really bad on dark backdrops though.

The TV flickers frequently as well. The tones will change between warm and light, there will be a pink glaze across the entire display, and even the display itself will flash green and take the shape of an hourglass.

I'm really hoping I can fix this problem by replacing something in the TV that's going bad, and that the replacement parts won't be too costly. If I can fix it myself for under $70, it's worth it to me.

Thanks in advance!
- Ya Dad

Sounds like a fault in the green channel feeding the CRT. Lack of green will look like there is an excess of red and blue so it takes on a pink or violet hue. It would tie in with green flashes too. The zig-zag lines are caused by the spot retrace not being blanked. The picture is scanned from top to bottom and normally the CRT is blanked as the beam returns to the top for the next scan, what you see is the spot still lit up as it returns to the top.

The fault could be many things and I'm not familiar with that model but my starting place to look for faults would be the circuits on the CRT base board. I suspect it has three almost identical transistor amplifiers on it, one for the red signal, one for green and one for blue. The green one should be checked for dry solder joints. If they are OK, the next likely suspect would be the green channel driver transistor.

Don't worry about the hourglass issue at the moment, it may just be a side effect caused by the green channel making the CRT draw too much current and overloading the scan or high voltage circuits.

Brian.

betwixt said:

Sounds like a fault in the green channel feeding the CRT. Lack of green will look like there is an excess of red and blue so it takes on a pink or violet hue. It would tie in with green flashes too. The zig-zag lines are caused by the spot retrace not being blanked. The picture is scanned from top to bottom and normally the CRT is blanked as the beam returns to the top for the next scan, what you see is the spot still lit up as it returns to the top.

The fault could be many things and I'm not familiar with that model but my starting place to look for faults would be the circuits on the CRT base board. I suspect it has three almost identical transistor amplifiers on it, one for the red signal, one for green and one for blue. The green one should be checked for dry solder joints. If they are OK, the next likely suspect would be the green channel driver transistor.

Don't worry about the hourglass issue at the moment, it may just be a side effect caused by the green channel making the CRT draw too much current and overloading the scan or high voltage circuits.

Brian.

Click to expand...

So if the solder around the green signal transistor amp is dry, do I just add fresh solder over the dry parts? I have no experience with soldering and depending on the reply, I'll order a soldering gun and attempt to fix this myself. I already called in about getting this TV fixed and the guy over the phone said the inside of the CRT itself might have to be replaced, which would cost $250...

It is possible it's the CRT but they are generally very reliable and 'age gracefully' rather than show intermittent faults. I would have to see it to be sure but I'm guessing there is at least one ocean between us.

A dry joint is usually easy to spot, what happens is the component gets hot when running and returns to room temperature when the TV is turned off. Solder (at least when the TV was made) is a very soft alloy of lead and tin which gets moved by the expansion of the component and gradually fractures. Further movement by expansion can make the fracture open and close which breaks and makes the electrical connection again. Re-flowing the solder by heating it or applying a little more will bridge the gap and restore a permanent connection.

It may not be a dry joint of course, fractures occur inside components as well as in their solder joints and there is no cure except to fit new parts. It is worth checking the joints first though to avoid that expensive professional repair bill. I would suggest you buy a conventional soldering iron (25 Watts or more) and not a 'gun' as gun types tend to be difficult to handle and a bit 'brutal' when making small joints. You will need some solder as well, in many countries it is now illegal to sell lead/tin alloy so you might have to use a lead free type. It still works but doesn't flow as easily. You only need a short length so don't buy a reel full of it!

Brian.