1999 TV trouble

[gecko]

A TV that sat unused for a while but worked fined now makes a snapping/sparking sound when I attempt to turn it on, and then shuts itself off.

I am very familiar with older electronics, but I`m not sure where to start diagnosing this problem.

Specifically, it is a Philips Magnavbox el # 25TR19 C121 manufactured in 1999.

Thanks in advance for any advice you can offer.

 

[davenn]

is this a pic tube TV or a LCD/plasma type?

if a pic tube type, it sounds like possible EHT arcing across the back of the tube.

Dave

 

[gecko]

Picture tube. Not sure where to start on the arcing. I think that is what is happening.

 

[sheldonstv]

if its a crt then it could be eht flashover either from the final anode cap to the dag earth on the tube due to the anode cap perishing,or dampness around that area or a pin hole in the lopt or a dry /poorly soldered joint in the line op stage ... the list could go on for ever-ill look up the manual .......

 

[davenn]

Picture tube. Not sure where to start on the arcing. I think that is what is happening.

Hi Geko,

ok on the tube type TV, its a common problem for TV's that have been in storage or turned off for some time.
Sometimes its caused by condensation on the back of the glass tube and that ~ 25,000 volts arcs through the moisture and dust.
on rare occassions I have been able to look and see where the arcing is occurring and gently sanding with fine emery paper (sandpaper).
What happens is after a few arcs a carbon track builds up and that path allows contineous arcing. The only way to possibly stop it is to erase that track.

Soooooo ....
in a dark room with the light out and the back off the TV, get some one to turn the TV on for a few seconds then turn off whilst you look in the back from a safe distance and see if you can see where its arcing.

report back with your findings

cheers
Dave

 

[gecko]

picture of sparking location

Dave,
I have attempted to show where it is sparking in the attached picture. Have other pics if needed.

Thanks!! Alan

 

[davenn]

Hey Alan

ah ha thats the line output transformer and that thick cable coming out of the top of that cap is carrying the 20,000 or so Volts to the picture tube. its the other end of where I was initially expecting the problem to be.

Now you need to let that fully discgharge before playing with it give it a day at least.
Personally , coz of experience I get a well insulated handle screwdriver with a long shafted blade, Connect a crocodile clip lead to the screwdriver blade and the other end to a grounded chassis point on the TV. and then slide the blade point of the screwdriver under the ultor cap on the back of the tube. Thats the ~ 2inch diameter cap with the other end of that thick cable. You will probably hear a zap as it discharges.
It pays to leave it there a while as residual charge can linger. !!!!

Once the tube is discharged you can then clean and closely inspect that arrowed part in your pic. You can already see that there is a bit of blackening there caused by the arcing.
Chances are that the transformer will have to be replaced. BUT and this is a remote possibility BUT, haha you may be able to clean and scrape away the arcing trace (track) across the transformer "plastic" material.
That really depends on ...
1) how deep in the carbonising of the track has gone into the plastic
2) if the arcing is coming down from under theat rubber cap and down the black plastic
3 or if there is just a "blow hole" in the plastic down lower ie. virtually right at the tip of the arrow where the EHT voltage is escaping

do a really good clean around there, DONT scrap yet, take another close up sharp pic, then scrape clean and take pic again and let me see the results

cheers
Dave

 

[gecko]

cleaning

How do you recommend cleaning it?

 

[davenn]

I just want you to wipe with cloth, clean for a start so you can photo it and see if we can narrow down the origin of the arcing.
slide that grey cap up off the top of the transformer wipe and photo

Dave

 

[gecko]

pics

Thought I had posted these. With the rubber cap off, looks like it is one piece of molded plastic into transformer?

 

[gecko]

pics

Here are the pictures.