ikegami monitor no color issue

[Bill R]

I have an ikegami tm20-80 monitor that is loosing color. Color is fine when first powered up, but drops out after only a few minutes. Sometimes I get the no burst indicator, and sometimes there is simply no color. I reflowed a lot of questionable solder connections on the NTSC board around the 3.58mc crystal. Reinsstalled the board and color was back for hours last night. This morning same problem, ok for few minutes then no color. If I leave it off long enough the color will return, but only for a short period of time. I would like to have a schematic or service manual. If anyone can help it would be appreciated.