I'm seeing white! - Videokarma.org TV - Video

YamahaFreak · #1 07-07-2015, 04:39 PM

A friend of mine has dropped off his elderly grandmother's TV set to see if I can fix it. It's a crap mid-2000s Durabrand/Sylvania/Funai 13" CRT. The issue is that the picture is VERY bright, like a flashlight even. (In the attached screenshot, the boxes with text at top right and bottom left are supposed to be jet black!) I actually had to tone down the G2 control to get any picture at all - before this, all you could see was white. When there is no signal, the screen is properly black, but the TV menu text appears blown out. There are also several horizontal lines across the top section of the display. (These lines do not appear with no signal.) I know this TV is probably not worth it to fix, but I didn't have the heart to tell my buddy that, because his granny apparently is attached to this set. I offered him a very similar all-black cabinet Sylvania and he said if possible, he'd rather get the Durabrand repaired. After examination it appears this TV has been left on for most of its life. Lots of dust, and slight burn on the CRT around the edges of their cable box's raster.

EDIT: I apologize for the incorrectly rotated image. I don't know why this is happening and it's outside of my control.

rca2000 · #2 07-07-2015, 04:54 PM

This sounds a LOT like the loss of the video bias voltage to the collectors of the V-out transistors on the CRT board(possible one or three IC'S istead). This is around 200 volts, sometimes as high as 250, sometimes as low as 170. it almostr ALWAYS comes from the flyback--through a rectifier and cap.

Thee is a resistor in line with the diode from1 ohm to 10 ohms usually.. and it sometimes OPENS, sometimes due to a shorted diode. . As a result...the cathode does NOT get its "positive bias" and tends to float towards ground through the driver. This results in excessive broght ness and weak, often negative video.

Findm-Keepm · #3 07-07-2015, 09:39 PM

Quote:

Originally Posted by rca2000

This sounds a LOT like the loss of the video bias voltage to the collectors of the V-out transistors on the CRT board(possible one or three IC'S istead). This is around 200 volts, sometimes as high as 250, sometimes as low as 170. it almostr ALWAYS comes from the flyback--through a rectifier and cap.

Thee is a resistor in line with the diode from1 ohm to 10 ohms usually.. and it sometimes OPENS, sometimes due to a shorted diode. . As a result...the cathode does NOT get its "positive bias" and tends to float towards ground through the driver. This results in excessive broght ness and weak, often negative video.

+1 - the diode, the resistor or both. NTE552, we used an RCA diode (Thomson made BYV26D/E, 1A, 800V or so, fast recovery).

As to the image rotation, it's set by modern digital cameras in the EXIF file. AK and VK for some reason either strip it, or reassign landscape/portrait. No worry - we all need the exercise...altogether now..and a TILT, 1, TILT, 2, TILT, 3...

radiotvnut · #4 07-07-2015, 10:07 PM

I've fixed a few Funai sets with this problem and they used an underrated glass diode in the supply for the video output stage. This diode will short and burn up the resistor that is associated with it. Replace the diode with a heavier one and replacement of the resistor usually fixes the problem. If these parts are good, check the electrolytic capacitor in the supply line (usually between 2.2uf and 10uf, at least 200V). If all that is good, junk the set and find her another 13" TV.

radiotvnut · #5 07-07-2015, 10:09 PM

Those lines at the top of the screen may be caused by a faulty boost capacitor in the vertical circuit. It will be located near the vertical output IC and will likely be either a 100uf or 220uf (may possibly be a 47uf). This is a high failure part in all recent CRT TV's and if it's not attended to, it will eventually burn up the vertical output IC.

YamahaFreak · #6 07-08-2015, 11:58 AM

Thanks for the tips! I'll take a look-see and follow up when I find something.

YamahaFreak · #7 07-09-2015, 08:40 PM

I'm having trouble locating the suspect components. Am I looking on the mainboard or the CRT board for the diode and resistor? As for the vertical booster capacitor, there are two caps near the vertical IC heatsink that could be it; one is a 100uF 160v (nearest the yellow transformer) and one is a 47uF 160v (nearest the flyback) in the photo.

rca2000 · #8 07-09-2015, 10:14 PM

Pretty sure that is NOT the vertical area...I see a SMPS transformer--looks like the power supply.

As for the 200 volt diode and capp--likely it will be near the flyback, and colse to a connector that leads off to the CRT board. It will come right off of a flyback pin--usually through the resistor and then to the diode and cap (perhaps a 4.7/250 ,10/250 or such) and then to the CRT board.

radiotvnut · #9 07-09-2015, 10:31 PM

The vertical IC will likely be a stand-up device on a small heatsink. The capacitors in this area will likely be no more than 50 volts.

YamahaFreak · #10 07-09-2015, 10:33 PM

Perhaps this is what I'm looking for? Resistor and diode at edge of mainboard, near cable leading to CRT board, though the diode isn't a glass one. None of the other capacitors match the suggested values to look for.

I think I've found the vert IC - a seven-pin device resembling a large transistor, that's mounted to a heatsink near the tuner. (It's visible at lower right.)

rca2000 · #11 07-09-2015, 10:44 PM

It is VERY likely that 7 pin IC. and one of the three caps near it--maybe C551, near the yoke connnector. if not tha tone--one of the 2 other electrolytice near it. One says c554, can't see the number of the orange one.

As for the diode--it does NOT have to be a glass one--and that one next to the 1.8 ohm resistor looks like a prime candidate to me. The cap will likely be one of the two electros near the diode.

rca2000 · #12 07-09-2015, 10:45 PM

DO NOT--replace that diode with a normal 60HZ one--use an ECG 552 or such. It is a fast-recovery diode..

YamahaFreak · #13 07-09-2015, 10:52 PM

C551 is a 47uF 35v, C554 is a 100uF 35v, and the orange one, C562, is a 2.2uF 50v. The two caps near the diode are a 1uF 160v and a 4.7uF 250v.

If I'm using my limited experience with a meter correctly, the resistor is not open (in-circuit) and the diode tests open in one direction, which I assume is correct.

rca2000 · #14 07-09-2015, 10:54 PM

Then you need to take the meter and see what the voltage is on the cathode of that diode going to the CRT board. It mUST be at least 170 volts or higher--with respect to cold ground.

if it is on htere...then trace the connector to the CRT board and see if there is the same voltage on the re. SHow me a pix of the CRT board--front and back--and I may be able to help you a bit more.

YamahaFreak · #15 07-09-2015, 11:17 PM

Here is a photo of the component side of the CRT board: