Nothing to do this morn so............
Mark everything so you can put it back if needed.
From Sams manual, edited.
Set brightness & contrast to mid range.
Color level off ( CCW )
Pull service switch out ( will get a line )
Set R, G, & B color bias controls CCW
Set R, G, & B drive controls CW
Set screen control CCW ( on CRT socket)
Advance screen control til a line JUST appears either R, G, or B.
Adjust the other 2 BIAS controls to make a white line.
Push service switch back in.
Hopefully now you have a good B&W picture now.
If not use the DRIVE controls to make it B&W. If
you cant your CRT prob weak. When done one of the
DRIVE controls should be still CW & one of your BIAS
controls CCW.
Try that & let us know how you did.
73 Zeno