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]] | ||
Revision as of 12:45, 28 June 2024
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. Other times, it is necessary to spray some cleaner into the pot.
Many of the potentiometers in Tektronix instruments are parts Tek bought. Some of the potentiometers were made by Tek.
1960s stop-less potentiometers
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).
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.
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:
| Type | Resistance | Used in |
|---|---|---|
| 311-068 | 500 kΩ | VAR GAIN in Type Z (R7620) |
| 311-304, 311-309 | 185 Ω | VAR GAIN in 3A74 (R426) |