ibm portable squished image

[soviet9922]

Hi after using my new-old ibm portable for a couple of months today the display started to act in a bizarre maner.
Slowly and in front of my eys the image started to compress in the center in a jittery way and now is stuck in that position.
Not sure if this is a common problem or somebody have any idea whay this happens (this only show on the internal amber display)

 

[NeXT]

Vertical deflection is failing. That or your vertical height adjustment is acting up.
You will have to go into the shielded analog board assembly and see if either a cap or two has started to really give out from age or if the yoke harness has come loose.

 

[T-Squared]

There might be something wrong with the vertical sizing potentiometer. I'm not familiar with this system, but I can immediately tell it's an adjustment problem.

 

[vwestlife]

If it has a vertical size control (not sure since I haven't seen the internals of the 5155's CRT), shoot some contact cleaner spray (like Deoxit) into it and turn it back and forth a few times. That was the cause of my Tandy CM-11 monitor's image getting jittery and sometimes collapsing -- a dirty vertical size control.

 

[soviet9922]

Thanks guys, the vertical trimmer pot was dirty like you say just a matter of cleaning and adjusting it again.