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Potentiometers: Difference between revisions
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Potentiometers are a common source of problems in old scopes. | '''Potentiometers''' are a common source of problems in old scopes. | ||
Often, just working the potentiometer back and forth over its range is sufficient to rejuvenate it. | Often, just working the potentiometer back and forth over its range is sufficient to rejuvenate it. | ||
Other times, it is necessary to spray some cleaner into the pot. | Other times, it is necessary to spray some cleaner into the pot. | ||
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Many of the potentiometers in Tektronix instruments are parts Tek bought. | Many of the potentiometers in Tektronix instruments are parts Tek bought. | ||
Some of the potentiometers were made by Tek. | Some of the potentiometers were made by Tek. | ||
==1960s stop-less potentiometers== | |||
In 1962, Tek-made potentiometers started being used in many instruments. | In 1962, Tek-made potentiometers started being used in many instruments. | ||
These are typically identifiable by their gray delrin cover (and their Tek part number). | These are typically identifiable by their gray delrin cover (and their Tek part number). | ||
They are "stopless" pots, which means that they have a detent but can be rotated through the detent. | They are "stopless" pots, which means that they have a detent but can be rotated through the detent. | ||
This feature was intended to reduce shaft and pot problems that result from excessive torque on traditional pots. | This feature was intended to reduce shaft and pot problems that result from excessive torque on traditional pots. | ||
[[File:Tek 311-0304-00 pot.jpg|thimb|350px|right|Tek-made pot, part number 311-0304-00, VAR GAIN in a 3A74]] | |||
File:Tek 311-0304-00 pot.jpg|Tek-made pot, part number 311-0304-00, VAR GAIN in a [[3A74]] | These types tend to develop cracks in the cross-shaped plastic part that clamps the shaft using a setscrew. Tightening that screw then causes the crack to widen, and the shaft is not clamped strongly enough anymore, causing it to slip. | ||
Some types affected are: | |||
{| class="wikitable sortable" | |||
|- | |||
! Type | |||
! Resistance | |||
! Used in | |||
|- | |||
| [[311-068]] || 500 kΩ || VAR GAIN in [[Z|Type Z]] (R7620) | |||
|- | |||
| [[311-304]], [[311-309]] || 185 Ω || VAR GAIN in [[3A74]] (R426) | |||
|- | |||
|} | |||
[[Category:Repair issues]] | [[Category:Repair issues]] | ||
[[Category:Electromechanical components]] | [[Category:Electromechanical components]] | ||