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Tektronix 556 Fan Motor Repair Part 1

Posted on January 19th, by Shaun Merrigan in Electronics, Oscilloscopes, Tektronix 556, Vacuum Tubes. Comments Off on Tektronix 556 Fan Motor Repair Part 1

Tektronix 556 Fan Motor Repair Part 1

I was recently fortunate enough to acquire a Tektronix 556 Dual Beam Oscilloscope with many accessories and in good condition.  Unfortunately, the cooling fan on the scope was very loud and more concerning, it emitted an alarming metal on metal contact sound.  After verifying basic operation of the oscilloscope, I decided to repair the cooling fan.  This process is documented in the images and commentary that follow.

Part 1: Removing the Noisy Fan Motor

556 Cooling Module with filter and mesh screen removed.  The fan is connected to the chassis wiring at the ceramic terminal which is circled:

556 Fan Cooling Module Outside

Fan to chassis wiring connection terminal.


556 Fan Cooling Module Fan Connections

Inside of cooling module and bottom side of motor (fan blade removed):

556 Fan Motor Underside

Back side of motor (fan blade removed).  This is a 4 pole 1725 rpm (loaded) motor.  It moves a very large volume of air.

556 Fan Motor Rear

An  inspection of the cooling module showed that:

  • The fan blades were mounted “backwards” reducing their efficiency
  • The fan blades were not hitting any of the heatsinks or wiring
  • The “metal on metal” noise was coming from the motor itself
  • There were indications on the motor itself that it had been taken apart before

That covers the overview and mounting of the fan motor. After desoldering the wires connecting the motor to the chassis wiring, I removed the fan and mount (blue frame attaching the motor to the rest of the cooling module) as a unit.  Then I removed the motor itself from the mount.

Part 2 will cover what I found when I disassembled the motor itself, and how I repaired it.

Thanks for reading.

Shaun M.

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