[jshorva65]

The most important consideration (aside from the obvious ones such as compatibility with 70-degree color chassis of any kind in the first place) in using a test rig with a particular model of 70-degree color chassis similar to one which it supports directly is matching the impedances of the respective yoke windings in the rig to those of the set's own yoke within a reasonable tolerance. For both windings, +/-10% is preferred, while +/-15% is about the maximum tolerable degree of mismatch. Most 70-degree color yokes will typically have similar impedances, within +/-20%, as an educated guess. Uncontrollable vertical "rolling" seems to be the most frequently occurring symptom when operating test rigs with 70-degree color chassis when there is a moderate mismatch of convergence ballasts. Of course, a severe mismatch could easily damage the rig or the chassis, or both.

The importance of avoiding CRT "burn in" on the rig, but especially the prevention of damage to the picture tube in the set under test, cannot be overstated. Burn-in is damage which not even a CRT rebuild can correct. Just like a snapped neck, the only cure for a badly burned screen is a replacement tube. Both of my "daily use" 5AXP4 tubes for B/W bench testing, my "spare" 5AXP4 tube, and my 8XP4 and 8YP4 tubes all show signs of having been operated without deflection at least once before I acquired them. When using these tubes, I insert them into the yoke of the chassis under test or disconnect the set's own yoke and connect the extension cables of an appropriate B/W "substitution box" unit (basically, the B/W equivalents of the CK3000, using either a 5" round or 8" rectangular test CRT) to all of the appropriate connections on the chassis under test. The tubes in these units have pre-existing "dead spots" in the center of their screens from prior misuse, but are still capable of producing a picture adequate for troubleshooting purposes. Until I can locate undamaged examples of them (probably would have to be NOS, since ALL "used" tubes seem to have been MISused at least once), my existing tubes will just have to suffice.

When performing grayscale setup of a color chassis, during which the Service switch will disable vertical sweep, it is very important to preset all three G2/Screen controls fully CCW and set CRT Bias and Brightness to completely extinguish the raster before placing the switch in the Service position. Failure to do this could permanently damage the set's own CRT in a matter of mere seconds. The MAXIMUM brightness of the Service line should be just barely visible in a dimly-lit room. Grayscale setup procedures outlined in textbooks on color TV servicing and/or service literature vary somewhat for different textbook publishers and/or set models. Some will specify that the Service line should be barely-visible, while others will state that the G2/Screen controls should first be set to the point where the line just appears and then backed off to the point at which the line is just extinguished.