Tektronix 2465A DV Oscilloscope Siemens Hall-Effect Sensor Controlled Fan Motor Rebuild: Part 1
I imagine that most of you have seen my article on the replacement of the memory back-up battery in my Tektronix 2465A DV Oscilloscope. If not, you can click on the link and read it.
After I repaired the backlight in my Sanyo TV, I started hearing a small sporadic rattling sound coming from my Tektronix 2465A DV oscilloscope. It was definitely coming from the Siemens fan motor. I don’t like taking unnecessary chances, so I decided to rebuild the fan motor before the problem got worse.
The motor is a Siemens #1AD-3001-0A Hall-Effect sensor controlled fan motor. You can see in the photo above that I managed to get the fan impeller off of the rotor shaft without breaking it. Many people break the impellers trying to remove them. I was afraid that I would break mine because it did not want to come off.
I looked online and could only find one company, Q-Service in Greece, that had a fan impeller – and they only had one left. I went ahead and bought it just in case I broke mine. It was only $10 USD. I went to the Tektronix service manual and followed their directions and the impeller came off easily without breaking it.
My scope, as well as other scopes, use the Siemens #1AD3001-0A Hall-Effect sensor controlled fan motor. My scope uses the Siemens fan motor because it has the DMM option, Option 01, a 4 ½ digit fully autoranging DMM.
The photo above is my scope with the DMM board open. It is on a hinge and swings open so that I can get into the scope through the cover behind it and remove the low voltage power supply board that the fan motor is attached to.
There are many different types of scopes so I will not talk much about opening up the scope. I will just mainly concentrate on rebuilding the Siemens fan motor. That is going to require more than enough photos for this article.
In the photo above you can see the fan motor and primary filter e-caps in the power supply. Below you can see them with the cover removed. The housing cover and power cable is removed so that all I have to do now is lift the motor with its board up and out of the fixture that holds it.
I could not find much information at all about these Siemens fan motors. The only article I could find about rebuilding them is from Matthew D’Asaro at Antique Radios Forum. His article was a big help since I did not have to go into this rebuild blind.
I decided to write more detailed articles with many more photos to help people out who may wish to rebuild their own fan motors. Thanks Matthew!
My goal in writing these articles is to show people that rebuilding the Siemens Hall-Effect sensor controlled fan motor is not as scary or difficult as a lot of people seem to think that it is. Besides being inside some of the Tektronix scopes that don’t have a letter after the scope number, the Siemens fan motor is also in lettered scopes like mine that have the DMM option, and possibly in some other oscilloscopes and test equipment.
I would imagine, and I think I read about it somewhere, that they used this fan motor because it runs very quiet with very low vibration. A lot of times I would feel at the back of my scope to check if the fan was working because I could not hear it running!
I contacted Siemens about the fan motor and they told me that everything concerning the fan motor was sold to a company called Continental.
I called Continental and was told that they had no information about the fan motor anymore. Continental must have trashed everything they had about the fan motor and they didn’t even have anything in their computers.
I called Tektronix also and they do not have any information on the Siemens fan motors other than what is in their manuals. So that turned into a loss.
We really do not need more information on the fan motors to rebuild them than the manual provides anyway. But, it would have been nice to have more information and some provenance that I could include into these repair articles.
In the photo above you can see the top of the fan motor board. The power cable is still attached at the bottom right corner. The main transistor Q1698, beside the power cable, is a PNP high current transistor Tektronix Part #151-0622 with an Ic(max) of 2A. It was made by Motorola. Close-up photos of it are below.
The number that is actually on the transistor is Part #614-0622. I can’t find anything on that number. According to the Tektronix Semiconductor book, it is compatible with the #MPSW51A. Mine checks to be good with no leakage. According to my checks, MPSW51A is outdated and unavailable. So I will replace it with Part #MPS751-D26Z.
The U1690 IC, #156-0281, is a 14 pin DIP four NPN high current transistor array. According to the aforementioned Tek Semiconductor book, the transistors are compatible with the #2N3725. I can only find #2N3725A transistors. So I will replace the array with four of these.
The RT1696 Thermistor is a 5K 10% NTC, Part #307-0124-00. I will replace it with Part #NK502C1R10. I will also replace the five diodes #1N4152F with Part #1N4152-BK.
I am not sure if I want to change the hall-effect sensors. I will study up on them and think about it later. If the need arises to replace them, I can do that without the need to unsolder the board or unwind the coils again. So changing them is not that important at this time.
All of the resistors checked to be good. Hopefully all of the replacement components will work well and the fan will run fine for another 30 years!
In these photos above and below you can see the fan motor removed from the power supply board with the fan motor board still attached.
I would not recommend trying to remove the fan motor from the board without a good desoldering gun with a 1.6mm tip. If you do not have a desoldering gun you will probably have to use Chip-Quik. It is not an easy job even with a desoldering gun. I used my desoldering gun and I did not use Chip-Quik.
Just don’t put any pressure against the solder pads on the board. Take your time and be careful. Don’t spend too much time on a pin and get it too hot!
Test the pins and see which ones still have solder holding them. I had a few pins that were hard to get free. When one starts to get too hot, let it cool down and then desolder it again. Adding a little fresh solder can help sometimes.
Eventually you will get them loose. Don’t pull on the fan motor while you are removing the board. Carefully wiggle the board, applying gentle pressure with your thumb on the pins, until the board comes off of the fan motor.
In the photo above I am opening the lock crimps around the top and bottom of the motor. Be very gentle with this process. The metal of the fan motor housing is pretty soft, so all you have to do is just slide the screwdriver blade in between gently and spread the crimps open a little bit.
I put a blue dot on the housing and the top end piece so I can put it back together in the same place. But it does not matter since mine can only fit on one way, but I don’t like to take unnecessary chances. Just take your time and be gentle and you should have no trouble.
During the rebuilding of the fan motor, I will refer to the end of the fan motor where the impeller fits onto the shaft, as the top of the motor. And the end of the fan motor that solders into the board, as the bottom. After you have all of the lock crimps loose, remove the top end cap and set it aside.
** Do NOT pull on the bottom cap or you may damage the Hall-Effect sensors! **
When you have all of the lock crimps opened up on the bottom, hold onto the fan motor housing with the top facing down. Put the top end of the rotor shaft on wood/rubber or something soft enough not to scratch or mar the end of the rotor shaft.
Then slowly and gently press down on the fan housing so that the fan motor starts coming out of the bottom, as in the photo above. I pressed mine down against the anti-static mat on my table.
When the housing bottoms out on your table, or whatever you use, you can push the rest out with your finger on the end of the rotor shaft, or hold onto the fan motor and gently pull it free from the housing. Be careful and don’t get in a hurry!
After you remove the outer housing it should look like the photo above. Now carefully remove the tape from the Hall-Effect sensors on the end cap. Place the tape in a safe place if you want to reuse it.
Here is a closer look at the two Hall-Effect sensors. I could not find any numbers on them. Take a marker and mark the end cap between the Hall-Effect sensors and the fin of the plastic inner rotor housing – notice that I marked mine with a red marker. Carefully pull the end cap off of the windings a little ways so that you can see the coil wires.
This is a photo of the bottom of the end cap before I removed the epoxy. You can see the pin numbers. You need to clean out the epoxy they used to plug the adjustment hole in the bottom end cap. I have found that alcohol will soften the epoxy up some to make it easier to remove.
Just be careful and take your time. Anything that you break may not be replaced without buying another oscilloscope to salvage the parts from.
Now with the end cap off a bit, we can see the eight wires from the coils. Four of the wire endings are soldered to pin 9. I cut them first and marked each one with a piece of masking tape with #9 on them.
Then as I cut each wire, I marked it with the pin number it was soldered onto. As you can see in the photo above, the wire is marked 13, which it and one of the number 9 wires are the 4th coil as wound, or the 1st coil as it is unwound.
You can call it the 1st coil if you want to, or the 4th coil, that is up to you. But technically, it is the fourth coil because it is the last coil that you will wind when rewinding the motor.
I am going to number the coils as they are numbered when being wound from the start. So the first coil to be unwound during disassembly is coil number 4, or the 4th coil.
Here is a wider view of the fan motor with the 4th and 3rd coils removed. There are only four wires total. Each of the two wires winds two coils that are at opposite sides of the rotor housing, and wound in opposite directions.
Each coil is wound with 135 turns. Removing the 4th coil, I counted 135 turns. Then the wires went to the other side of the rotor housing to the 3rd coil, and I counted another 135 turns removing it also.
Here I have the 4th, 3rd, and 2nd coils removed. Coil #1 is still on the rotor housing. The 4th coil started with pins 13 and 9, and ended at the end of the 3rd coil with pins 9 and 10, respectively.
The 2nd coil starts with pins 11 and 9, and ends with the end of the 1st coil with pins 9 and 14, respectively. I will go into winding the coils in greater detail in Part 2, along with the schematic, when we reassemble the Siemens fan motor.
If you want to use brand new magnet wire in rebuilding your fan motor, like I will, then you need to order some 34 gauge heavy film magnet wire. It should have a diameter of 0.0075” (0.19mm).
I am using new wire because I do not want to take a chance of wasting my time removing/unwinding this fan motor again. Reusing the old wire would just be asking for problems, IMHO.
Here we have all four coils removed. You can see the clear plastic rotor housing with the rotor inside. Remove the end-play set screw from the bottom if you have not done so already.
Now it’s time to carefully take the rotor housing apart and remove the rotor. Set the rotor aside somewhere where it will not attract metal to it. Take your time and be careful – you do not want to break the plastic rotor housing!
If you find some metal pieces sticking to the rotor you can remove them with masking tape.
Here you can see the bottom Oilite Spherical Bronze bushing. You can see the oil washer under the bushing and the steel star lock ring that keep the parts in place.
In the photo above you can see the top bushing components in the top that are still in place. You will also notice that the Oilite bushing has a steel washer on it that goes in between it and the rotor. Be careful and do not lose this washer.
If you do lose the bushing washer you can find another one. The dimensions are: OD= 4mm, ID= 2.10mm, thickness= 0.11mm. SAE dimensions are: 0.1575”, 0.0825”, and 0.0040” respectively. The washer is steel, and it is magnetic.
Above I am using a 10mm socket to carefully push the four ends of the bushing hold-down star tab down so that I can twist it CCW and remove them from the slots that lock them in.
Be very careful! All you have to do is just get the ends started – once they are started on the lips, you can use a screwdriver or something and push them the rest of the way loose.
You must take your time and be careful! If you break anything you may never find another one without buying another scope to salvage parts from! And it might have a different model number.
I am not sure how many different model numbers there are of the Siemens fan motors. I know that there are at least two that I have heard of.
These are the bottom bushing components. They have not been cleaned yet.
These are the top bushing components before they were cleaned. Notice the little steel washer that was between the rotor and bushing.
Here is a photo of the screwdriver slot side of the rotor shaft end-play set screw.
Here we see the business end of the rotor shaft end-play set screw as it looked when it was removed from the rotor housing. I need to clean the surface and polish it up good.
The two photos above are of the Oilite Spherical Bronze bushings. They are both the same size of 4.45mm-OD, 2mm-ID, and 3mm long.
I ordered four of them from Patrick at lm-tarbell.com. I have not received them yet. Small orders are not worth much money and he is very busy. Maybe if enough of you guys order some of the bushings from him to rebuild your own fan motors, he will hurry and make a batch! Of course, I cannot finish the articles without those bushings.
So if you are following along and want to rebuild your own Siemens Hall-Effect sensor controlled fan motor, you can order your components, wire and bushings, and get ready for Part 2. Hopefully there will be a Part 2 and 3.
I will stop this article here. There are already 32 photos in this article. In Part 2, hopefully, we will finish rebuilding our fan motors. And then in Part 3, we will test and scope the fan motor on the bench utilizing my new Siglent SDS1204X-E digital oscilloscope!
Others say that they reuse the wire that they remove from the fan motor during disassembly. Personally, I do not like that approach unless you have no other choice.
Magnet wire is not very expensive. Plus, reusing the old wire makes the motor less dependable. So, why ask for trouble?
And don’t forget that you need to get two rolls of wire because you will be winding two wires together at the same time. Or transfer about 600 feet to a second spool. Six hundred feet on each spool should be more than enough.
Here is a photo of the schematic of the Siemens fan motor board for those that would like to see it now. There are two resistors on my board that differ from the schematic. I will enhance the schematic and make changes to it in Part 2.
See you in Part 2!
Robert Calk Jr., is a Hobbyist from the U.S.A. that loves Electronics Device Repair. Please leave any comments or suggestions that you may have below. Thanks.
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