seems that the main logic board which supplies the video signal is good, your problem, more than likely , is with the chassis board mounted to the monitor. The monitor should be able to be pulled directly out to the machine. there are some guides and a spot to hold the two posts on the side. when you pull out the monitor, there will be a id plate on the back of the chassis, probably will read 1492, probably needs to be recapped, might solve the problem. you could contact KLAR electronics repair (there link is on the top of the page) they should be able to take care of this.
they should be able to instruct you as to how to remove the chassis from the frame. not difficult at all, just be cautious of the HIGH VOLTAGE LEAD connected to the tube, this voltage is usually bleed off in a period of time, however it is always safe to short this out to the frame before removing it, other than that it is a simple matter of removing the wires and connectors, take a good picture of where everything is connected so when you re-install it you will have a guide.
Hope this helps
JIm