Need help with repair of Tatung 14428 board

[Badbaud]

The monitor comes on with a beautiful picture but within 10 minutes white vertical retrace lines appear and get brighter and the picture begins to fuzz up.

Replaced all of the big and medium size electrolytics and the LA7851 but condition still occurs.

Any suggestions would be appreciated.

Also does anyone know where to get a replacement FBT for a 14428 with a 15 inch screen?

[Downunder]

Sounds mre like or of the ic on the neck board is caving in.

[cowboygames]

Normally I would suspect one of the two things you've already tried, caps and vertical output, but the retrace lines could be either a failing FBT or just the screen control on the FBT. Other possibilities of course but that's where I'd look next. Unfortunately a bad screen control may require a new FBT as they are hit or miss for repairing though you may be able to at least identify it as the cause of your problem. The CRT board is possible but an unlikely culprit

[Badbaud]

Another bad FBT ?

That's two in one week and Tatung says there is no way to find a replacement.

Bummer is local shops charge $700 for a flat screen replacement, Not many home owned-ers want to spend that kind of money.

[cowboygames]

Any chance you have another machine you can swap that board into to see if the problem stays with the board? A carbon short across the electron guns can cause a fuzzy picture and retrace lines also. Thing is, I wouldn't expect it to need to warm up to do it if that was the case

[Badbaud]

No, and I had put the tube on our Sencore and knocked all of the dead electrons off of the guns.

Think I will try lugging the 25" chassis out of the machine and connect it with an extender and try hitting certain components with some freeze spray to see if any of them are causing the problem.

[cowboygames]

If you can get it turned on outside the machine try tapping on the neck of the tube with a plastic screwdriver handle after it starts acting up. Just be careful you don't crack the sob or get the guns shacking to much. Sometimes you'll have floaty pieces of carbon that tapping will dislodge. Zenith had a trainload of tubes in the mid 90's that were notorious for carbon buildup and we fixed a lot of them with a sencore and a screwdriver handle. Good luck...

[Badbaud]

Ya, been there did that the first day we started working on it.

Set the Sencore on extended and tap on the tube neck with the blunt end of a screwdriver.

Got all of the guns from 2 notches into the red up to all full green.

Will try some freeze spray next Monday with the monitor out of the cabinet.

[satchsquatch11]

Been awhile since I worked on one of those but I seem to remember a cap next to the flyback that always went bad, I think it was non-polarized. Can't remember the value but I just put a polarized version with the same value in its place. Just my two cents. 

[Badbaud]

4.7uF / 50V np, already replaced that part.

They always look fried and when they start to go bad the picture width widens beyond the edge of the screen.