what damage - flyback focus adjustment

[blackevilweredragon]

my Commodore monitor was starting to just, show it's age..  it wouldn't show things clearly anymore really...

So, as always, I took it apart in a quest to fix it..  On the flyback transformer, I knew to look for the "Focus" port on it's divider circuit, and sure enough, I found it, I cranked it completely clockwise till it stopped, and the picture on the Commodore monitor is absolutely STUNNING!  much clearer than its EVER been, and I'd say it's competing with my fathers 32" TV (SD, not HD)..  actually, i'd say the Commodore monitor looks BETTER than my fathers TV, in clarity..

But I wonder, am I doing any damage to the monitor by squeezing out this extra life?

[rt9342]

I don't think this should damage it - I've done the same thing to many monitors before, as well as other adjustments, such as adjusting color bias whenever black and dark gray look like a certain color.  Once, I've seen a TV burn out not too long after doing bias adjustments, but I think this could be due to worn out circuits that were already fixing to go bad (after all, the bias wouldn't of gotten off in the first place, if something wasn't aging, right?).  So I guess there's a slight risk that you may wear it out faster, if the focus was off due to a wearing-out part, but most likely you shouldn't have to worry about it, unless the focus had gone from good to bad in a short period of time (which is what happened to that TV that I had the color bias problem with).
But then again, you said it's turned all the way clockwise - that may be a sign that something's on its last leg - possibly the tube.  I once had a monitor that just wouldn't go in focus at all, so I replaced the tube with one from a dead monitor and it worked, but I had to adjust all of the gains, biases, focus, etc., as well as reverse a couple of yoke wires, as the picture was upside down.  But the replacement tube, even though a different type, worked after that, with crystal clear picture.  My suggestion is just run it as it is and hope you get at least a few more years out of it.
Just to let you know, too (maybe you already know this): if you still have any problems with white objects looking a little phsychedilic around their parimeters (may be more noticable on the outer edges of the screen), or scan lines seperating into red, green, and blue lines, this can be adjusted too, without damaging the monitor, though it's kind of dangerous for whoever makes the adjustments.....and VERY tricky too.  Those brown rings around the neck of the tube (just behind the deflection yoke) adjust the color alignments.  But I'd leave those alone if the picture looks good - you can easily get shocked by deadly power on the tube, and you can make the picture worse if you can't figure out the correct alignment.  Older TVs used electronic adjustments, which were somewhat easier - the magnetic rings are more of a cost saver, I believe.

[viletim!]

Of corse it's ok to make adjustments to make the unit work properly again. Speceificaly regarding the tube focus voltage... what tends to happen is that the resistors in the voltage divider circuit (several maga-ohms in value) start to 'go high' (increase in resistance). You can compensate by adjusting the focus control but once these resistors start to go high there's no stopping them. Eventualy you won't have enough range on the focus pot and you'll have to replace the line output transformer or do some surgery to it.

Not to be confused with a tube fault where you can't acheive focus (there's plenty of range on the pot in both directions but the best spot is still out of focus).

[blackevilweredragon]

well, being i had to turn the POT completely clock-wise to get an amazing picture, im sure it could get better..  it's actually got better focus than my 27" HDTV right now...

though, I couldn't focus my HDTV, it's POTs were glued.. why did they do that?  and is that normal for a company to do?

[ido8bit]

In more recent TVs and monitors I've found the focus/screen pots (and often other adjustments) glued more often than not.  The glue can usually be picked off easily.  Often it will come unstuck on the first attempt to adjust the pot.  It is safer to pick the glue off first as I have snapped the shaft off one pot when I tried to adjust it without noticing that it was glued.

[blackevilweredragon]

I'll try picking off the glue...

Why do they even bother to do that?  To make it so we HAVE to get it serviced by a professional, who will just get the transformer replaced and charge a ridiculous amount of money?

[viletim!]

Perhaps they've had problems with the pots readjusting themselves. They are mounted on a transformer (which vibrates a bit at the line frequency) after all. I don't think i've ever had a problem with this....just stick a screwdriver into the shaft, turn, and glue breaks off.  

[blackevilweredragon]

i tried turning it on my fathers transformer for his monitor, but it wouldn't budge, instead it was bending the circuit it was soldered onto..