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RX-02 repair advice..

B

bjones

Member
Joined
Mar 18, 2011
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21
Location
Orlando, FL
I'm working on rebuilding a pair of RX-02's in my 11/34. While one drive turned out OK, the other is a bit more of a challenge mainly due to the condition of the AC motor. The motor is not turning very well and very dirty, I was looking at how to take it apart and rebuild but it looks like the halves are epoxied on. For those with experience, is there a way to attempt to clean these motors without disassembly or is there a method to tear them down and rebuild?

Thanks much!
/brian
 
So, I was hoping somebody would respond so I could learn from the discussion. I also have an RX02 but it's still under the desk in the office and not yet restored. Have been using an RX02 emulator with the 8/M, which works great, so restoring the real RX02 is lower on the priority list of vintage computer projects.

It looks like greasy-sticky dirty stuff on the outside of the motor, which is fairly common in other stuff I've restored. Probably what you see on the outside of the motor is also on the inside. This was the situation with the fan motor in my PDP-8/M power supply. Tried to clean it from the outside using Q-tips and alcohol but that wasn't sufficient. I ended up taking the entire motor apart to clean the inside. The fan motor runs great now, after a thorough cleaning.
 
Blast it out with high pressure compressed air would be the easiest thing to try, this should remove dirt between the armature and stator coils at least. And then you'll know if the bearings are cactus.
 
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Unfortunately I don't have a photo of the fan motor disassembled. This is how it began...
IMG_7311.jpg

Tried to clean around the blades using Q-tips and an old washcloth...
IMG_7323.jpg IMG_7324.jpg

which made it look nice from the outside, but there was still dirty-sticky stuff inside. Parts that rotate have a small clearance inside of this motor. I removed that clip you see in the last photo (there were actually two clips at different levels of disassembly) and was able to take apart the motor. After cleaning the inside it spins like a new motor.
 
I would be surprised if there is no way of pulling the RX02 motor apart.
The tricky bit is finding out how. Here are a few ideas:
  • Apply gentle heat (about 100 degrees Celsius) to the epoxied section and see if it comes apart (pull, twist).
  • Investigate the purpose of all the visible bolts and rivets.
  • Try to find another junk RX02 motor (Ebay?) and use it as a "sacrificial" and brute force the disassembly to discover how to do it properly.
  • Alternatively maybe you could find some way to X-ray it at an airport.
  • Find a "electrical motor rebuild" company. They have likely come across this type of motor assembly.
 
gwiley said:
So, I was hoping somebody would respond so I could learn from the discussion.
Click to expand...
I haven't had to mess with the motor other than to clean belt and adjust motor position to tighten belt some. Belt was slipping which made drive flaky. Haven't had any belt trouble with the other drive in the box. You may be the first to try to disassemble.
 
Word to the wise: Running an RX02 for very long without the fan is not a good idea.

I left mine running an XXDP diagnostic to exercise it while I took a dinner break. The room was air conditioned and the fan was running normally.

However, a sticker inside the plenum took that opportunity to come loose and jam the fan.

Upon my return the "magic smoke" smell was very obvious and an almost working RX02 now needs some further attention.

So..... Even in an air conditioned room, the RX02 needs forced air cooling. Note that yours probably has a charred area on the PCB near the stepper motor drivers.

The documentation says if the charring gets too bad, you should call DEC field support to have the board replaced. Yeah, like that's gonna happen.

When I dig back into mine I'm planning on trying to add heat sinks instead of trying to save a few pennies like DEC apparently did.
 
If I recall the screws on the sides hold the ends on but you would have to take off the fan and front pulley, perhaps with a nice bearing puller.

Or you could clean out the motors, then lubricate the shafts with 3 in 1 oil and see how that works. It's an AC induction motor, so no brushes to worry about.
 
bjones said:
This is the motor in question.
Click to expand...
So, I just did this on an RX01 drive the other week... same motors, but different fan design. Both were nearly seized. I had to use a syringe/needle to get oil (synthetic ATF in my case) into the bearings on both sides of the motor and worked them back and forth quite a bit to free them up. Once I was satisfied, I powered them up and let them run for an hour or so -- they're both spinning quite nicely now.

The stepper motors were both completely seized and I had to get fairly aggressive with them to get them freed-up and spinning nicely. I ended-up using ATF on these as well and they both spin like new now... actually took me a good hour just on that alone.

-Chris
 
DDS said:
Word to the wise: Running an RX02 for very long without the fan is not a good idea.

I left mine running an XXDP diagnostic to exercise it while I took a dinner break. The room was air conditioned and the fan was running normally.

However, a sticker inside the plenum took that opportunity to come loose and jam the fan.

Upon my return the "magic smoke" smell was very obvious and an almost working RX02 now needs some further attention.

So..... Even in an air conditioned room, the RX02 needs forced air cooling. Note that yours probably has a charred area on the PCB near the stepper motor drivers.

The documentation says if the charring gets too bad, you should call DEC field support to have the board replaced. Yeah, like that's gonna happen.

When I dig back into mine I'm planning on trying to add heat sinks instead of trying to save a few pennies like DEC apparently did.
Click to expand...
This is interesting, the RX01 in my DEC CLASSIC (desk machine) does NOT have a plenum fan on the back, and never did from the factory as evidenced by the official documentation:
1688093467426.png<-- As seen in the manual

1688093563101.png <-- Mine

This was quite surprising to me as I originally thought the fan/fans were missing, but indeed the system never came with any! I'm guessing that DEC thought the fans on the spindle motors moved enough air to cool the logic as well. Other people have mentioned that (early) RX01 drives were known to have shipped w/o a plenum fan (or any other fans for that matter) on the back.

-Chris
 
The drive mechanism of early RX01 differ from later RX01 and RX02. The earlier was made in cast aluminium while later was made out of aluminium sheet metal. One of my RX01 also looks like that while the newer has fans. Maybe the drive mech has built in fans in the earlier model. I have not taken it apart so I don’t know.
 
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