Vertical collapse - What part?

[RayB]

Super-Ken, I expect you'll have an answer here

I have a Taito style cocktail table (probably from '80 / '81).
I don't know what monitor parts are still original, though I do know at least the tube has been swapped...

I was testing a game out and the monitor would intermittently completely "collapse" so it only displayed a line of graphics across the middle.  I noticed that gently hitting the monitor frame would bring the picture back to normal. This tells me there's something loose, maybe even a solder joint issue. Thing is I don't know where to start looking. What part controls the vertical drawing? First thing I would check is the V-Size pot, but what else?

[Ken Layton]

I would start with pulling out the monitor main board and looking for bum solder joints (which can be anywhere on the board).  Get yourself a good strong light and a high powered magnifying glass to look with.

[RayB]

Just to be clear is a solder joint pretty much any solder point holding in a component leg? Or is it something else?

[elvis]

I had the same thing in a cab I bought off eBay about a year back.  Turned out to be a hairline crack in the vertical control part of the circuit (it was just enough to break the trace on the PCB - probably happened during transportation).  I just soldered in a bit of cable to jump the break, and the problem went away.

And yes, a good pair of eyes helps.  I didn't spot it at all, but a mate who spends a bit more time with a soldering iron found it after about 5 minutes of up-close searching.

[Doughbroz]

Bad solder joints will usually be found around the components that heat up the most, like the flyback and big resistors, and don't overlook spots where wires are soldered onto components hanging from the sides of the chassis.  Bad joints are usually easy to spot--they are no longer shiny and the area around them may be discolored.  Don't just add solder to the pile around a bad joint if you can remove it, and CAREFULLY scrape any corrosion off the component leg before resoldering it.  After it has cooled, GENTLY scrape away any flux that might be touching other solder pads or their traces.  Before starting, clean the solder wire by gently pinching it in a paper towel and pulling it through a few times.  Getting it nice and shiny removes contaminants that cause a poor solder joint.