Monitor screen flashing and arcing in cabinet

[GM81]

This started Yesterday, when I first turned on the machine the screen would flicker and make a sort of popping sound. It only did it a few times and stopped for the rest of the day. This morning it did it again, but was constant. After opening up the cabinet and turning the machine back on I could see the arcing. Has anyone else had this happen? I am not sure what to call this component and if it is replaceable by itself. Please see the picture to know exactly what I am talking about. For now I just wedged a piece of plastic between the black unit and the sheet metal guard to stop the arc.

Thanks for reading. The picture res was huge so I just make a link to it instead.

http://i.imgur.com/q2jto.jpg

[Al_The_Man]

That is the Horizontal output transformer, commonly known in N.A. as the Flyback.
It produces the VHV for the CRT, (9kv for monochrome, 15kv for colour).
Either the insulation has cracked and it is arcing to the adjacent components or Moisture, humidity or general dust contamination can also cause the arc across.
You need to inspect it closely and clean the transformer and the lead to the crt.
The CRT can store the DC charge for some time, so be carefull if removing it from the CRT connector.
Al.

[GM81]

Thanks for the reply, Al. I will inspect it on Monday to make sure all juice has drained. If indeed the case has cracked, is that transformer replaceable or do I need to get a whole new board?

[Al_The_Man]

A big IF you can find a replacement H.O.T., the board has to be removed and a dozen or so printed circuit pins have to be de-soldered.
If it is just insulation cracked, I would try a clean with a non-residue electronic cleaner and attempt a repair by filling with an epoxy.
Cracking is usually a sign of overheating, but if it is still working OK, it may be just age.
Al.

[GM81]

Okay, I will give it a shot Monday and hope it is that simple. Thanks again!

[john_100]

look carefully where the red EHT cable plugs into the line output transformer you may be able to find a pinhole burn mark

if some one switches the monitor on while you look in the back of the monitor
you will see where the arc starts

with luck it will be either from the cable or what looks like the black heatshrink sleeving covering the joint

once you have discharged any EHT to the chassis
you can replace the cable or remake the connection and replace the heatshrink sleeving

if its the transformer you may be able to use a two part epoxy (araldite)
or non corrosive silicone sealant ,eg:-
Buy Silicone Sealants Non-corrosive silicone sealant,Wht 100gm RS 2974304 online from RS for next day delivery.

ordinary diy silicon sealant gives off acidic fumes as it cures

a new LOPT ( line output transformer )
will be more expensive

note - even when the power has been off for a few days a high voltage can be present ,the CRT can store a large charge (as I know the hard way ! )

to discharge the tube you need to make a connection between the braiding
that connects to the conductive coating on the back of the cathode ray tube
and the EHT connector on the tube
(the EHT probe for a multimeter is ideal as the rounded point does not scratch the tube and also internal resistance limits the current)
but if you use a screw driver connected to the braid be very carefull !!!

John

[GM81]

Thanks for the reply, I should of mentioned this in my first post but if you zoom in on the picture you can see where the arc is hitting the metal guard, the arc starts at the same location on the transformer. I was planning on using Hysol 608 Epoxy becuase I have cases of the stuff.

[Al_The_Man]

If on the lead, it could be a split on the heat shrink insulation covering the in-line HV rectifier that is in series with the H.O.T. output as soon as it leaves the transformer.
If so, you can actually get wrap around heat shrink tube, as you would not be able to get seamless tube over the CRT connector.
Heat shrink in conjunction with RTV also works on flexible applications.
Al.

[john_100]

Hi Al

do you mean self amalgamating tape ?

http://docs-europe.electrocomponents...6b8001b6fa.pdf

John

PS another variation is "liquid insulating tape" :-
http://www.sotabeams.co.uk/liquidtape.htm

have not used it my self but could be usefull on the wiring to the limit switches on cnc machines ?

[Al_The_Man]

Hi Al

do you mean self amalgamating tape ?

Looks like the same item, RayChem sell a similar product in N.A.
Al.

[neilw20]

A big IF you can find a replacement H.O.T., the board has to be removed and a dozen or so printed circuit pins have to be de-soldered.
If it is just insulation cracked, I would try a clean with a non-residue electronic cleaner and attempt a repair by filling with an epoxy.
Cracking is usually a sign of overheating, but if it is still working OK, it may be just age.
Al.

Hey!!
Don't use epoxy. It is hygroscopic. You really don't want a water sponge as an insulator.

A silicon PCB conformal coating is much safer, or hard wax you can melt with a soldering iron. Put the PCB in a (conventional) oven at 100°F, 40°C for 4-6 hours or leave it cook in the sun before coating if you must fix it. You need to drive away any moisture. Do you have a vacuum chamber?

The retest to see that it not arcing, before coating.

Be aware there may already be carbon tracking on the surface and that must be repaired first.

Look to see where the arcing is. Don't fix what is not broke.

And after discharging the tube, wipe all of the tube around the HV (ultor) connection with isopropal alcohol.
Don't use methylated spirits. It leaves some sugary stuff behind.

[GM81]

Sorry for the delayed response, we ended up using some heat shrink tubing and it seems to have done the trick. I hope it lasts :]

Thanks for all the input.