loading

Fixing a old tv that shorts out?

So i have this old Magnavox projection tv, hasent been run in a long time due to a shorting issue between a heatsink and something (its been so long that i dont even remember) I can plug it in and find excatly where its shorting but i dont want to fry the tv...
I do remember that it is one of the heatsinks by the flyback that it arced from.
I also have the basic wiring diagram for the tv, but it only shows how to adjust the picture, what connects to what and, what wire is what.
Should i try and turn it on again and find where its shorting and possably fix it, or just call some tv repair guy who knows more of what hes doing.

sort by: active | newest | oldest

Back when you could make a living as a TV repair man I repaired TVs.

Look first and see if you can see burnt or broken insolation on wires or components.

Look for bugs hiding in tight places and yes I mean the six legged kind, insects.

Replace all damaged parts and clean all dust and debris from wires and components.

As a TV repair man we always turn on the TV and see what happens.

Turn off the lights and turn on the TV. (Arcs show up better in the dark.)

If it is still shorting make carful note of where.

Arcing usually leaves a burn mark.

Shorts can be caused by dust, debris, and insects, however in your picks the circuit boards look clean.

I would say from experience it is from a defective flyback or somewhere in the high voltage circuitry. (Wires can loose their insolation value.)

If the TV is old good luck finding new parts if you can get new parts you may have to buy the whole circuit board.

It is a bit dusty on the inside but i noticed no bugs what so ever.

eailer i pluged it back in and was going to get a video when it shorted out, and well.. it didnt short out at all, worked fine, other then the channel down button didnt work but im not worried about that. but i didnt notice a loud hissing/static sound coming from around the power supply board, didnt poke around it or anything because it was on.

also.. as for the burn marks, i looked on the heatsinks and didnt see any and all the wires look fine

That is good that the TV works and bad that you can’t see the arc.

Did you check for the arc in the dark they can hide between the flyback coil and the flyback core.

Hissing is a symptom of an electrical leak, (arc) and what it means is there is a loose connection, weak insulation, a dust buildup, or a combination of the last two.

Work with one hand in your pocket ware insulated shoes; stand on a shock mat or both.

This is to assure current doesn’t go in one hand across your heart and out the other hand or out your foot.

Checking for loose.

Work with one hand in your pocket ware insulated shoes, stand on a shock mat or both, and using a nonconductive or insulated tool make sure everything is tight. (Wires, heat sinks, components, and circuit board mounting.)

Checking for weak insulation.

Work with one hand in your pocket ware insulated shoes; stand on a shock mat or both.

I like analog meters set for 1000 volts or more for this testing.

Clip the negative lead to the neutral of the circuit board then turn the TV on.

With one hand in your pocket take the positive lead of the meter and touch it to the insulation of the wires as you watch the needle of the meter. Move the positive lead up and down the wires and if you get a good reading on the meter there is a leak. Check the flyback coil insulation also.

Leaks can be fixed by replacing the wire or leaking component, or you can add insulation.

Dust can add to a leak.

Cleaning the dust can be done five ways.

Work with one hand in your pocket ware insulated shoes; stand on a shock mat or both.

1.If you have an air compressor you can blow off the dust.

2.With a dry paint brush; brush the dust off.

3.Brush the dust and blow it off with compressed air.

4.Use a vacuum with a brush attachment.

5.Any of the above and wash with methanol. (Make sure to drain all stored charges first, methanol burns.)

I dont see any arcing, but i was thinking it might have something behind the board, is it safe to power up the board without it being booked up to anything? (and for the flyback i can just have that power go to ground through jumper cables, thats how i disassembled the tv/crts i had)

You can power it up disconnected from the chasse and all the wires connected to the TV, just remember to use a jumper from the board to the chasse if the screws ground the board to the chasse.

is methanol safe for plastics?

I had an issue with burnt carbon on a car instrument cluster causing random flickering of the idiot lights (even when off). after taking everything apart i used some CRC QD electronic cleaner and wiped the traces. Not sure what caused the shorts in the first place but it removed the carbon enough to not cause the flickering.

You indeed were a TV repair man, very good advice !

I would attempt to find the arc short.

After vacuum and clean follow the high voltage lead from the tube to the flyback.

Remember the high voltage will remain dangerous even after the unit is powered off.

You would not believe the number of times the repair was caused by a cockroach.

Did you know they chew on wires?

The high voltage remains dangerous with the TV off and unplugged.

You can short out the stored charge through a resistor.

If you know where .... which brings to mind the machine repair man being questioned by the shop admin about a $100 bill for tapping a noodle part.

Anyway after some conversation the indignant admin wanted a bill breakdown and got the following.

  1. $ 1 for taping the machine noodle
  2. $ 99 for knowing where to tap hammer !
  3. ------
  4. $100

...




thats just like taking your car to a dealership. $60 parts $450 in labor, for 2 parts!

I like that one.

petercd3 years ago

Powered off and all dangerous voltages discharged(especially capacitors), I might try looking for burnt insulation on all the nearby wires in the area of arcing, arcing is usually due to broken insulation, although with HV it could be a pin prick in size... however it might be a good idea to have a pro look at it because the voltages you will come across can kill, resulting in a personal re-incarnation experiment at best.