> > I have a BA11K power supply out of a pdp 11/34 that has frozen up fans. > They are frozen up pretty bad. I heard from another list member here they > are repairable, any advice on how to do so?
I have repaired many fans over the years, I am not sure if I have done those ones specifically. First remove them, take off any grilles, finger guards,etc so you are left with the bare fan. Then, assuming an AC fan (I am pretty sure the ones in a BA11K are 115V AC), measure the resistance between the terminals. If it is totally open-circuit, then the winding has failed. Rewinding is often possible, but not trivial, particularly not for something that has to stand mains voltage, and you may decide it is better to replace the fan. If the winding seems OK (or if the fan was running, albeit with a lot of noise, before you started this), then it's time to take it apart and deal with the bearings. Theres is little consistency in how fans are assembled, alas.. Very occasionally, the outer housing is in 2 parts, held together by screws on one side. If so, separate that first. You now need to find out how the spindle and rotor is fixed : Look for a cap in the centre of the blades held down by a circlip. Remove the circlip, the cap, oil felts and washers (keep them in order) and you will see a tiny circlip on the end of the spindle. Take that off, then any washers (which may be keyed to the spindle) and slide out the blades/rotor OR If there are screws on the hub of the blades (uncommon, but I have seen it), undo those and remove the blades. This reveals the motor, there is a little circlip on the end of the spindle as above, remove it and slide out the rotor OR There may be screws hidden under the label on the other side of the fan that retain the motor stator. Take those out and carefully separate the motor from the housing. Carefully, so as not to damage the wiring connections. Then again there is a circlip, remove this and separate the rotor from the stator. OR The worst on is to have a cap hidden under the label. Once you have found this, remove it, then the circlip (getting familiar now), washers, and pull out the blades/rotor from the other side. Now for the bearings. These will either be sleeve bearings or ball races. If the latter (more common in DC fans) you can extract them from the housing and either replace (they will be a standard size) or take the covers off, flush out the old grease with a suitable solvent (petrol (gasoline) is good, but of course highly fammable), and repack with high melting point grease. If sleeve bearings, try just cleaning everything and relubricating with machine oil, If that doesn't help, you can extract them, but will probably have to make (rather than buy) replacements from phosphor bronze or similar, which needs a good workshop. This sort of thing is worth doing on the PDP11/44 with its odd fans, possibly not on more common ones. -tony
