Response from Jonathan: Philip,

Have you tried adjusting the horizontal and vertical hold/sync adjustments? That would definitely be the first place to start. Also, double check your sync wiring from the board to the monitor to make sure it is hooked up properly. Sometimes you have to combine and/or separate the sync wires in order for the monitor to accept them. We discuss this a bit in our post and video on Replacing An Arcade Monitor. Check that out if you haven’t already.

So, try the adjustments, double check your sync wiring, and make sure that the b+ voltage is dialed in. If all that checks out, then you may have a problem with the sync on the monitor chassis. You can identify this area by tracing back through the chassis from the sync input pins. Check to make sure that all the components in this section are working properly. If you have additional questions about this, please let us know the make and model of your monitor chassis and we’ll try to help you out further.

Hope that helps. Thank you for your question and good luck with your repair.