TWO DRIVE BELTS WERE IN BAD SHAPE
A pulley in the machine steps down the speed of the AC motor to produce 300 RPM at the print clutch cam shaft and 111.6 RPM at the print wheel. The print wheel spins through the 48 characters that the printer can produce, thus it takes just over half a second to complete one rotation.
Any print line that uses all 48 of the characters would need about 0.54 seconds to print on all the columns with all the characters. Spacing down one line in order to print the next line on the page takes approximately .2 seconds, allowing time for the print wheels of the last character being printed to finish movement and for the carriage to move down one line.
This means the absolute maximum rate that lines with all 48 characters can be printed is about 1.36 lines per second, roughly 81 lines per minute. Lines with fewer characters can finish when the last character that exists on the line has been printed. For example, lines with only numbers could print around 110 lines per minute. A standard page at 6 lines per inch vertical pitch has 66 printable lines, thus the printer barely prints faster than 1 page per minute.
There is a belt from the motor to the pulley, and a second belt that runs from a different circumferential ring to the gear train that links the print clutch cams and the print wheels. These had sat in a fixed position for decades, thus the rubber set into the shape and would thump for quite a while until (if) it relaxed to neutral shape. Worse, one of the two belts had a tear from the inside edge almost all the way to the outer edge, which would cause the belt to completely fail in a short time.
NEW BELTS WERE PUT ON THE PULLEYS
I measured the belts, which where 1/2" width standard V belt shapes, and found new belts of the correct size which I could order. When they arrived, I installed them on the pulleys. A protective metal shield covers the belts and pulleys. Fitting that in place around the belts and pulleys was surprisingly difficult. It required a staged assembly - removing a top plate, leaving the center pulley too lose for proper belt tension, installing the metal cover, then reinstalling the top plate. After all that, the belt tension gets set with the belts mostly hidden under the cover!
ADJUSTING AND TIGHTENING CENTER PULLEY TO ATTAIN DESIRED TENSION
The nut on the back of the center pulley axle is accessible from behind the covered belts and pulley. A lug behind the nut allowed me to pull the pully axle to achieve a good tension in both belts. I tested by poking a finger through holes in the metal cover, tweaked the axle position, then tightened it up.
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