Upright arcade

[Pinballrocks]

 I bought an upright arcade machine.
 I have a problem with the screen. When i turn machine on every thing is perfect but after about 5 minutes the
 lower part of the screen starts to distort. the longer the machine is on the more the screen distorts. It looks like 
 image is bending to the right.

 Thought i would ask if anyone knows what this might be? seems to get worse the longer it is on.
 

[Pinballrocks]

 I failed to mention that the left hand side lower corner of the screen looks dark and that is where the screen
 appears to start distorting from. I hope my discription of the problem is not too difficult to under stand.

[Strangeways]

This would most likely indicate a dry solder joint on the chassis. To isolate the chassis, have you got another gameboard to try ?

I would not attempt to repair the chassis unless you have experience and an understanding of the high voltages that are present.

What you can try is adjusting the monitor (via the trimpots) after it has distrorted. Could be vertical size or vertical sync depending on the orientation of the screen.

If one section is darker - it will be the chassis. I had the same issue with one of my cabinets recently.

[Boots]

Probably the monitor chassis is quite old and the capacitors are all dried out.
Once it warms up you get the distortion.
You could also have a dry solder joint somewhere that is causing it, as it heats up the conductivity gets worseand so does the picture.
You could try replacing the caps or just go to Jomac and get a new replacement chassis.
Just be very carefull when disconnecting the chassis from the picture tube as there are VERY high voltages present and they will give you a nasty zap.

[Boots]

 I failed to mention that the left hand side lower corner of the screen looks dark and that is where the screen
 appears to start distorting from. I hope my di******ion of the problem is not too difficult to under stand.

Hmm that does sound slightly different.
Does this darkness change if you rotate the machine around?
Usually a colour distortion like that sounds like magnetic interference or it just needs degaussing.

[Pinballrocks]

 I dont have another game board to try. I might try turning cabinet around to see if colour changes and degause it.
 I am not real keen on playing around with the chasis/ picture tube as i have heard about the nasty shocks. I will try
 adjusting the pots and failing that it is probably beyond me to repair. Thankyou all for your advise.