Wells Gardner k4900 Vertical warp on U.N Squadron

[dbowie88]

Hey, all.
    So I've had this cabinet for awhile, and I've spent a nice long time on refurbishing it without too much trouble. I've wired up the new jamma harness, cleaned and labeled everything nicely, replaced the controls, etc. Unfortunately, despite all my efforts on the monitor, its STILL giving me a lotta crap.
   Here it is when i first got the cabinet, running Radiant Silvergun 



   Since then, I have put in a new cap kit, cleaned up the transformers and monitor chassis, checked all the wiring (V sync was not composite with H sync), and looked into this problem extensively, but to little use. Here is the monitor running U.N. Squadron.





Better, but still off.

   It seems like the bottom portion of the image appears at the top of the screen in a slightly vertically-skewed fashion. Is this the vertical deflection? I've checked all the potentiometers on the monitor chassis; the only thing i havent looked into is the voltage on the B+. Please give me any useful information.

 Thanks.   

[Ken Layton]

Did you adjust the "Vertical Dampening" (vert damp) pot? This pot is not present on early production 4900 series. If misadjusted it can cause a vertical foldover.

[dbowie88]

  Yes. The vert. damp pot only squashes the top section of the image down, or stretches it up. There is also some text garble present- I'm hoping that is just due to this monitor issue. I have indeed tried all the pots though, and the caps are all new.
  Any more suggestions would be appreciated. Thanks again for your time.

[Ken Layton]

Vert Damp, Vert Size, and Vert Hold all interact with each other on this model. You'll need to tweak combinations of all of them.

[dbowie88]

  Again, I checked all the potentiometers. All adjustments to combinations of the pots and the monitor rings behind the cathode have done nothing to help the vertical foldover.
  One thing of note, however, is that the vertical dampening and vertical hold do not seem to make any sort of difference to the monitor when adjusted. Is it possible for these pots to wear out? I have a galvinometer; could i check to see if the voltage is changing at all when the potentiometer is turned? Otherwise, I'm at a loss for ideas.

[dbowie88]

Nobody has any ideas?

[Kevin Mullins]

Yes.... these pots get flaky with age.
You can check the pots with an ohm meter....

 A ----
        >
        <---- C
        >
 B ----

Ohms between leg A and B should be the total value of the pot.
Measure between A and C or B and C while adjusting it to look for the value change.

Do this with power to the monitor OFF . 

[dbowie88]

  Well i checked the pots with my galvanometer/ohmmeter, and i didn't really find any discernable problems (provided i did it right). Does anybody have any other ideas? Thanks.

[Cole]

mine did this after it was re-capped. suspect a cap in reverse polarity, or wrong value.

[Malenko]

mine did this after it was re-capped. suspect a cap in reverse polarity, or wrong value.

if you waited 4 more months you could have bumped a 10 year old thread.