jsnospam@cimmeri.com wrote:
Paul wrote:I think the electrolytic capacitors are quite likely to be the cause. I have an ESR meter which I built from a kit some years ago when I was doing a lot of monitor repairs. It measures the "effective series resistance" of electrolytic capacitors, and works in-circuit. They dry out with time and heat, and the series resistance rises.Paul, did you recall ever seeing a classic Mac with the whole screen image shifted slightly to the left.. as if its center was off? That's the OTHER problem I'm having with this Plus analog board... unrelated to ticking sound. Swapping analog boards solves the centering, so I know it's not the CRT yoke or logic board. I'm *assuming* a problem in the video or horizontal sweep circuits.. with some signal not being delayed enough by some minute fraction. While the Mac has a width control, it doesn't have a center control.
Although Paul's suggestion to use the centering magnets would certainly move the raster, the fact that it's fine with another analog board indicates that it's actually the sweep timing that's off, not the raster centering. The control you're looking for is the "horizontal hold" or "horizontal lock" or "horizontal frequency" control. It is often an adjustable slug in the horizontal oscillator coil (not the horizontal output transformer). Adjusting it usually requires a plastic or fiber tool with a hexagonal tip and a slightly smaller "shaft" that allows it to be slipped through the hole above or below the coil form to engage the hex-holed slug inside the form. A turn or less will adjust the phase of the horizontal lock without causing it to lose lock. The correct adjustment is usually about halfway between losing lock in one direction and losing lock in the other direction, and at this "midpoint" the raster should be approximately centered horizontally. The CRT centering magnets on the rear of the yoke can be rotated to complete fine horizontal and vertical centering. BTW, a marginal adjustment of the vertical hold will also move the vertical sweep phase, but to a lesser degree (since vertical sync is pulse locked, while horizontal sweep is usually phase locked). -michael NadaNet file server for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."