Monitor Fading to black

[SilverFerret]

Recently I had a problem with this monitor in which it wouldn't fire up. The rest of my gamemaker would work but the monitor wouldn't come on. On the suggestion of NLG members, I changed a few caps and its been working fine for a few weeks until I watched it fade to black and back on. It continued to stay on fine for another week or so when I noticed the monitor was black and wasn't coming back on. I left the machine off until I could have a chance to take a look at the caps, As I was examining the monitor, I noticed a focus dial and another dial that apparently will fade the monitor to black by turning it. I know this because I put the monitor back in and turned it on and it came on just fine and I adjusted the focus and turned the other dial and it went dark and I turned it the other way and it was bright again.
I had hoped it was a fluke that it faded to black but as I watched it for a few minutes it faded out again. It's a long and convaluted story but what does it sound like to you?
It's a Tatung monitor with very little if any burn in and worked great until these two issues.
Thanks for the help, Jim

[Slotmaster]

heat around the knobs will move them around just a tad when it heats up which is why they put a drop of glue on them from the factory and so they don't shift in shipping.    If it keeps doing it then use contact cleaner around the knobs and put a dab of hot glue on the them when in focus / brightness range.

Works for us all the time.


 

[SilverFerret]

I thought maybe the knob was the issue, but with the game on I watched it fade to black and as it was doing that I tried adjusting that knob which didn't help. It faded out not matter where I had that knob.

[Slotmaster]

I thought maybe the knob was the issue, but with the game on I watched it fade to black and as it was doing that I tried adjusting that knob which didn't help. It faded out not matter where I had that knob.

Simple thing to do is replace the flyback or hard for some but first try to clean (knob area) with contact cleaner, fixes many for us.   Dust  and dirt get inside there and cause all kinds of trouble. 

[SilverFerret]

So you don't think it's a capacitor issue or anything. The brightness dial is where you think the trouble is? It fades to black but my turning the dial doesn't bring it back nor does it ever go too bright instead of going dark.
Thank, Jim
P.S. What's the flyback?

[cowboygames]

The flyback is your high voltage transformer or HVT with the big red wire coming out of the top going to the tube. You might also check connections and caps in the horiz circuit. A can of cooling spray can be real handy in these situations. Spot cool componants when it goes out to see if it comes back, but you could easily have a bad flyback as stated above

[AnotherTech]

The focus and the other knob (high voltage) you were adjusting are on the flyback (FBT, flyback transformer, high voltage transformer, etc, they are all the same thing).  You want the adjustment on the high voltage to be high enough to look good (when the monitor is working), but not have white retrace lines through the screen.  

The fading in and out problem is probably another bad cap, or possibly a bad transistor or IC.  The cooling spray (also called freeze spray) cowboygames  suggested is a great idea if it happens when the monitor is warmed up.  Spray it on individual components on the board when the monitor blacks out.  If the monitor comes back on when the freeze spray hits a component, that's a good component to change.  

If you haven't replaced C331, I would try that.  It was a common failure.  Most of the failures on the Tatung monitors were caps.  
Some other common failures that might cause your problem were:
Q603
Q101
ZD620
as well as C106 and C109, which I think you already replaced.

Good luck.


Edit to add:  If you can get a good clear picture of the monitors board, I may be more help.  It's been a while since I've had one to look at, but I have fixed tons of these when we had them.

[SilverFerret]

Thanks a bunch. I'll give those a try.
Thanks again, Jim