Trashpicked CRT TV with the shakes (Excessive B+ voltage)

Picked up a M&S 20 inch TV from the garbage last week and since I was with a friend I lugged it home.

It didn't turn on but I could hear the main relay clicking inside when I pushed the power button, so it was clear that there was standby voltage but no B+

This TV sports a very prehistoric power supply design, using a STR50103 linear voltage regulator with a honking power resistor in series in order to step down and regulate the incoming rectified and filtered line voltage. No transformer here.

Turns out that a 470k 1/2 W resistor was open and the 130V protection diode was shorted and disconnected from the circuit, replacing the resistor got the TV working again but with a craptastic picture and the shaking you see in the video. The higher the brightness of the picture content, the stronger the shaking.

Replacing a couple of electrolytic capacitors around the flyback area improved the picture considerably. As for the shakes, it turns out the regulator was defective, providing an excessive B+ of 125 V while the nominal value for this particular regulator is only 103 V.

Needless to say, replacing the regulator got me a correct B+ and that stopped the shaking altogether. After adjusting the static convergence and the cathode levels I got a much improved picture, almost perfect from a TV that was salvaged from the scrap heap.

2011 Update: Since then I have rejuvenated the CRT by hooking up the cathodes directly to the 220V mains with a 15W light bulb in series while powering the filament with 9 volts DC. That improved the picture quality significantly. Now it lives in a spare bedroom of my house hooked up to a GameCube.

Category:

Science & Technology

Tags:

• CRT
• TV
• shakes
• shaking
• television
• set
• telly
• ripple
• voltage
• high
• EHT
• excessive
• B+
• linear
• regulator
• power
• supply
• STR
• STR50103
• garbage
• trash
• scrap
• current
• standby
• static
• dynamic
• convergence
• cathode
• color
• grayscale
• levels

[EarthwormJim55]

Does this TV have AV Imputs?

[133MHzz]

@EarthwormJim55 It does, although it's only got mono sound. Since then I have rejuvenated the CRT which boosted the picture quality quite a bit. It now lives in a spare bedroom of my house connected to a GameCube with a crapton of games.

[GruntofAction]

You've unlocked the special Earthquake setting on the TV.

[133MHzz]

@GruntofAction Funny that you mention it, since the 8.8 earthquake we had last February I've been picking up TVs like crazy, usually with cracked circuit boards due to falling, either people leave them on the curb or bring them to me.

After repairing the boards I keep the best ones for me and the rest gets sold or given away. Needless to say I've got TVs to spare now!

[GruntofAction]

@133MHzz

Speaking of TVs, you wouldn't happen to know how to fix color bleeding on a 2005 Sylvania 20 Inch CRT TV would you? It's got some minor red color on the outer edges and it's hard to read text on the screen.

[133MHzz]

@GruntofAction Bleeding highlights might be either a sign that the CRT is on its way out or a dried up filter capacitor near the flyback transformer, specifically the one that smooths out the cathode voltage.

Another thing is lack of convergence near the edges. Convergence is factory adjusted and doesn't move over the set's life. In that case either the TV fell down or something's wrong with the CRT.

I recommend you look up pictures of these kinds of failures to distinguish between them.

[segagenesis1989]

@Powowo

Correction ... that old crt tv is "jonesin" for some crack!

Withdrawl symptoms maybe? =P

[vestern22]

Hi, I have a question, I don't know much about electronics, recently due to power surge my dad's old CRT TV, Philips made 2000 model is not working anymore, is there any chances of the TV to get repaired or power surge fries TV completely, my dad told me he smelled some burning wires. The TV had automatic voltage regulator for 110-260V at 50/60Hz

[EarthwormJim55]

@133MHzz Thats really cool man! You should do some sort of video game collection video sometime.

[GruntofAction]

@133MHzz Thanks for the advice. The issue is minor anyway, and I'm probably gonna upgrade to an LCD computer monitor, which apparently doesn't have this color bleeding issue.

[PhatPhunk]

@133MHzz Ahh.. Didn't realize that! Wow, you sure know your stuff!!