Received replacement motor, installed it on the disk drive for the VCF 1130 system

MOTOR ARRIVED - ESSENTIALLY IDENTICAL EXCEPT FOR A SHAFT EXTENSION

The used motor I found on ebay was the same frame size and the rotation speed was within 1%. It has an extension on it, supposedly because it was used in a Bell and Howell 16mm projector. My first activity was to figure out how to remove the extension and end up with a shaft the same length and compatible with the blower rotor. 

Turns out the shaft itself is quite a bit longer. In addition, the ends bulge out a bit on the IBM version thus the mounting bracket that grabs onto the rubber bushings isn't a perfect fit for the new motor. 

I was able to bend the mounting bracket enough to hold onto the new motor. The longer shaft just extends farther inside the blower cage but does not impact anything. This means I can use the motor as is in the disk drive. 

PREPARED REPLACEMENT WIRING HARNESS

The harness used in the disk drive had the wires inside a metal mesh ground shield and then wrapped with  black plastic. It is fairly long to reach from the AC distribution box at the front of the drive around to the rear where the motor is mounted to pull air in through the SLT card cage and force it through a HEPA level filter into the spinning cartridge. 

The replacement motor had much shorter leads. I spliced these onto the original longer leads and pulled the mesh up to cover the extra wire. I then used long heat shrink cable to cover and protect the harness. 

The motor has a center tapped winding, main and starter. The circuitry has a relay that initially supplies AC across both winding since the switch closes due to the high startup current flowing through the main winding. When the motor is at full speed, the current should have declined enough to drop out the relay and the starter winding. This is a split phase AC single phase motor. 

REINSTALLED ROTOR AND CAGE ONTO THE MOTOR

A rotor inside a cage pulls in the air and blows it out into the plenum of the disk drive where it feeds the filter. That is attached to the motor shaft that has a flat spot, using a setscrew to lock it on. This was checked to ensure it would spin freely without rubbing on the cage. The SLT compartment on the drive has a filter on its front and a duct on the side which is the inlet to the blower rotor cage. 

BLOWER ASSEMBLY INSTALLED ON THE DRIVE

This was bolted into place and then the wiring reattached to the AC distribution box per the schematic. The filter and plenum cover went on so that I could verify a good flow of air when the drive turned on. The plenum is an open space in the bottom of the drive that is fed by the blower motor. It has a HEPA style filter installed at its outlet, which is oriented to the top of the drive.

The outlet feeds air inside the 2315 cartridge that was inserted into the disk drive. This blows out of the cartridge in the rear where the disk arm enters. Thus any particles are blown out of the drive and away from the surface where the disk heads will fly. A 90 second relay is included in the drive that allows the blower air to clean out the cartridge for that length of time before the drive attempts to lower the heads to the surface of the disk platter. 

Blower motor in place under disk drive

FIRST TEST TO VERIFY AIR FLOW

The blower motor runs any time there is AC power to the disk drive - in other words whenever the IBM 1130 system is turned on. I just needed to connect 120VAC to the drive to test the blower. I heard some noise but didn't feel air flowing out. The rotor wasn't turning. The motor didn't start turning.

I unmounted the assembly to work more easily with it. Turning on power again, I gave the rotor a twist and the motor was running just fine. The issue is with the start circuit. This uses a relay that should energize to turn on the start winding and then turn it off when the motor is at speed. 

I suspect the old motor winding burned out due to the start relay keeping it in circuit all the time. It is now failing to turn on the start winding thus the motor does not begin to spin. 

Start relay for the blower motor

It appears that the relay has an adjustment screw to control when the contacts disconnect because current in the main winding has dropped due to full speed operation. I may try to adjust this and test it, but the fall back is to buy a new starter relay.