CT-F1250 Reel Motor Rebuild (CT-F800/900/950/1250)

CT-F800/900/950/1250 Reel Motor Rebuild

Folks, I thought, since I was doing one of these for a fellow AKr, I would chronicle it. This rebuild is necessary for all of the following TOTL Pioneer Cassette decks:

CT-F800
CT-F900
CT-F950
CT-F1250

This motor works great for decades, but, nowdays, after 30 good years of operation, they all develop torque problems, and dead spots, where, if stopped manually, they will not start back up. The symptom for the overall deck is the play mode mysteriously stopping in the middle of a tape, for no apparent reason. What actually happens is the motor hits a dead spot while rotating slowly, and stops. The tape motion sensor detects the takeup reel stoppage, and stops the tape.

I've done several of these, and I still say, this is not a project for the faint of heart. The most difficult part is getting the little suckers open

The attached pic is of the motor we will rebuild...



Rich P

The first step is actually the absolute hardest in the process: Getting the outer case open. It is apparent that Pioneer did not intend for these to be opened or rebuilt. The outer case is swaged on, meaning the rear of the case has several swages, or retaining divets (distortions in the metal) driven into the edge of the main can, which keeps the end cap from coming off (it works too ).



You need 3 hands to do the job. That means you need someone who loves you to hold it for you (you don't want to clamp the motor in a vice lest you distort the case which would be disastrous). Then you need to use a collection of small punches and modified jeweller's screwdrivers, which are then used only for this purpose (cause you pretty much ruin the tips for screwing), to drive the divets out.

The motor is rotated, on its side, till the divet you want to work on is on the bottom. Then you begin to try to get the divet to bend back out of the way, so the endcap can clear it. There isn't much meat to work with, so you must decide in advance to be patient.

Once the divets are cleared, then you take another small screwdriver, and pry the endcap off, starting with the exit hole for the wires (be careful not to distort the endcap, it is very soft, or damage the wires or their insulation).

The pics show the endcap and divets of the outer case. Then the contents of the outer case are shown. The outer case houses a complete motor, a pair of silicone shock mounts (anti-vibration, so the deck does not hum , physically), and a mu-metal shield (to limit the magnetic field that gets out of the motor, imortant for tape decks with sensitive heads).



Rich P

The next step is to get the inner motor open (it actually has its own part number on a label). It is held closed in a similar manner to the outer case, except that the divets are much easier to access for driving out of the way. You will need to remove the motor pulley before you can open the inner case, but note its exact orientation and position, relative to the end of the shaft.

Be careful, as you open up the inner case, to ensure that you do not damage the brush assembly or lose any parts (especially the tiny polyethelene washers on each end of the motor) .

The next pics show the inner motor parts: the endcap serves as the base for the brush assembly, the armature (with its contacts, and speed regulator assembly), and the permanent field magnet (attached to the inside of the inner motor housing.

(Note the brush dust that has accumulated on the parts. Also, there was an excessive amount of oil all over the inside of this motor (not good). One drop of oil in each bushing is all you need, and you can't get to one of them till you disassemble the motor as shown.)





Rich P

Please, before we begin the correction of issues, remove the polyethylene washers from each end of the armature, carefully noting how many there are and the order of installation. If you lose one of these, or put them back on in the wrong order or location, you will have a paperweight.

Now for the first step of actual rebuild: burnishing the speed regulator contacts. The motor speed is regulated by running in three torque levels, governed by 2 centrifugal switches (switches with weights attached to their cantilevers). 1st state: high torque, with both centrifugal switches closed. 2nd state: Normal run torque, with the startup centrifugal switch open, but the over-speed centrifugal switch closed. 3rd state: reduced torque, where the motor speed is too high, causing the over-speed centrifugal switch to open. The torque will be reduced till the over-speed switch closes again. The motor normally operates right at this threshold.

One problem, here, is bad centrifugal switch contact resistance, caused by oil on the contacts, or contact corrosion and/or pitting. This will result in bad startup and run torques (bad enough to be the cause of the problems, all by itself).

Both sets of contacts on this unit were dirty.

I take a GC Electronics contact burnishing tool (PN #GC 93337, the small thin one), and add a bit of extra contact pressure while burnishing the contacts till clean and polished. Burnish only until the desired contact finish has been obtained, and use a 10x jeweler's loupe to look. There are 2 sets of contacts to burnish.

The attached pics show the speed regulator assembly. Study it until you can see how it works.






Rich P

The next step is to clean up the cause for dead spots in the motor rotation: corroded or dirty armature contacts, with worn high places at each armature contact cut point. I cut a thin strip of 1500 grit silicon carbide paper, gently clamp the motor shaft in a Dremel tool, and spin the armature at the lowest possible speed. Then, I gently use the strip of silicone carbide paper and remove just enough of the armature contact surfaces so that they are level again. Be sure to take off enough, but not too much. Stop and inspect with a jeweler's loupe (10x) at regular intervals, and stop when you are done. Take off no more that is absolutely necessary.

Note: Be very careful with this part! If you so much as touch an armature wire, while the armature is spinning, it will snap and you will have a pretty paperweight till you get another motor (don't ask me how I know )

Wear eye protection while turning the armature contacts (not optional!). Also, be sure to rotate the armature in the Dremel as slowly as you can get the Dremel to spin. If you don't, the centrifugal weights will break off and fly to Neverland, maybe even by way of your eye, or the weight cantilevers will be distorted and not function properly. If you can run your Dremel out of a variac, you can get slower speeds than the normal minimum. Also, I carefully and gently wire the centrifugal switches closed, using 30 ga wire-wrap wire, to prevent a launch, in case of an inadvertent over-speed during this operation.

This motor had hosed up contacts, so I could see why the dead spots were there.

The attached pics show the before and after conditions or the armature contacts, as well as the contact polishing process.

Armature Contacts - Before



Armature Contacts - After

Armature Contacts - Polishing


Rich P

The next cause for poor motor torque and dead spots is gummed up or dirty brushes. This unit had both conditions.

I don't have a source for new brushes yet (I'm actively looking though), but this unit still has plenty of brush life left. Believe me, even after 30 years, there is very little brush wear. I can usually still see the curvature originally put on the brushes at the factory. Simply use a tiny pencil eraser, like for a mechanical pencil, and clean the brushes. Use no fluids. you can get them clean enough dry, and you do not want to damage the brush composite.

Note: Under no circumstances try to reshape the brushes, with files or any other tools. If you do, you will not know if your rebuild is going to take until the brushes reform to the armature contact curvature, which could take weeks). If you square up the brushes, you will get burning of the armature contacts and brushes at the armature contact cuts (due to tangential contact points), and the motor will die and you will need to go back in

Also, do not modify the angle of the brush cantilevers, unless you must to increase the brush contact pressure (on the armature contacts, normally not necessary). You do not want to modify how the brushes lay on the armature contacts. If you do, you will have to run them in, and that may require you to go back in and re-perform the contact turning several times, to clean up the burn marks at the slots, due to tangential contact points.

The attached pic shows the brush assembly.



Rich P

The last step before reassembly, is to lube the motor. I use a light, Teflon lube (like Tri-Flow), applied with a toothpick. One very small drop in each bushing. Be careful not to get ANY lube on the brushes or switch contacts (paperweight time again).

Carefully reinstall the polyethylene washers, in the correct locations and installation sequences. Then, put the armature contact end of the motor into the brush assembly, carefully moving the brushes as needed.

Snap the inner case over the end-cap/brush assembly.

Power up the motor, and verify correct operation and good torque.

With a punch and hammer, carefully restore the original retaining divets (or make new ones) in the inner case to hold the inner motor closed.

Install the silicone shock mounts in the outer case, make sure that the mu-metal shield is fully seated and assemble it.

With a punch and hammer, carefully restore the original retaining divets (or make new ones) in the outer case to hold the outer case closed.

You are done. Congratulations

I'm going to bed ...

Rich P

Special Notes:

• Sometimes, you may need to go in and carefully repeat the motor rebuild. Sometimes it takes several runs at it, before the rebuild takes. This is especially if you changed the way the brushes ride on the armature contacts, in ANY way. You may need to take off a bit more, from the armature contacts, to make sure that any ridges or high spots are gone. Make sure you get no lube where it can get on the armature contacts. Make sure that you have the little washers where they go, in the right order and on the right side.

• One more thing, if the little belt that goes on the motor pulley is too tight, you will put burn marks at the slots in the armature contacts, which make dead spots (before the rebuild takes). I get that belt from Vintage Electronics, and I usually have to stretch it a bit, so it is not so tight. Be careful, because too much stretch and the belt will break while stretching it.

• When you finish, play several tapes, watching the voltage across the motor. it should be very close to 9vDC. It may take several hours of play for the new motor rebuild to take (brushes wear to good contact). Voltage of less than 8vDC across the motor is an indication that you have a problem with brush contact, centrifugal speed control switch contacts (inside the motor), or some kind of binding in the transport, or the small belt is too tight. You will know when the rebuild has taken, when the voltage across the motor remains up around 9vDC, with slight increase from cool to warmed up. The lower the voltage, the more current is being drawn (higher load, lower torque, etc.). Voltage will generally be good at first, then gradually go bad. Sometimes, I have seen the rebuild take, and seen the voltage jump up and stay good. Sometimes, 2 or 3 FF/REW passes of a tape will help a marginal motor past an initial weakness.

nice job!

an hour and 28 minutes :ntwrthy:

bolly said:

an hour and 28 minutes :ntwrthy:

Click to expand...

It took alot longer than that. It took that long just to post this thread. I finished the job before I began posting, taking pics as I went...

Rich P

I've said it before, and I'll say it again

you're a madman rich! :thmbsp:

Thank you so much, Rich! My 1250 is anxiously awaiting your work!

How did excess oil get in the housing? I know I sorta drowned the innards of the deck w/ DeOxit in order to keep it running for a while. Could that have worked its way inside?

mg196 said:

Thank you so much, Rich! My 1250 is anxiously awaiting your work!

How did excess oil get in the housing? I know I sorta drowned the innards of the deck w/ DeOxit in order to keep it running for a while. Could that have worked its way inside?

Click to expand...

It is common to think that the motor needs to be freed up, via lube, when the problem is really as described here. It appeared that the oil had been there for a while, in that it had gotten sticky, so I doubt that it was anything you did.

She should work real fine for some time to come :yes:

Rich P

Thanks for taking the time to post the thread. Nothing like learning from someone who knows what he's doing!
Great job!

Hey, I recognize my handwriting of the motor case. "CT-F 1250".
Ron

jblmar said:

Hey, I recognize my handwriting of the motor case. "CT-F 1250".
Ron

Click to expand...

So much for anonymity

Since the cat is out of the bag...be sure to let us know how it works, back in its place...

Rich P

I hope very soon.
Ron

Very informative. After hearing of someone out there who rebuilds these motors I decided to look into my 1250. I stopped right about there because I saw the case and thought I am going to fudge up the motor then I will be screwed. So this really helps out when I decide to tackle this job.

pustelniakr THANX! :thmbsp:

Was there any way to adjust those centrifugal switches ? (i.e. screw them up)
Photos are great, but nothing beats being there.

You define "chutzpa"..... anonymous motor....

How many gallons of sweat were expended?

I usually take risks on stuff I can afford to ding.
It leads to a little more relaxed attitude.

but don't get me wrong :ntwrthy: :ntwrthy: :ntwrthy:

(i'm still digging up the plastic polishing stuff)

markthefixer said:

Was there any way to adjust those centrifugal switches ? (i.e. screw them up)

Click to expand...

Do not attempt to adjust the centrifugal switches, or splay the contact cantilevers. The test/adjustment rig you will need is far too complex/expensive for one of us to construct. You will need a mini-dynamo-meter, so that the motor can be allowed to spin at varying speeds, with a dynamically adjustable clutch, while measuring speed, torque, and speed hysteresis effects, all at the same time. As long as you don't hose up the switches, the factory adjustments should suffice until the motor simply expires. Burnish the contacts, that should be enough.

Bottom line. Want to play with the centrifugal switches? You're a better man than I, Gunga Din

Rich P

pustelniakr said:

Do not attempt to adjust the centrifugal switches, or splay the contact cantilevers.
Bottom line. Want to play with the centrifugal switches? You're a better man than I, Gunga Din :nono:

Rich P

Click to expand...

NOPE :withstpd: NOT ME, "man's gotta know his limitations" (quote credit to dirty harry)..

I Just wanted to impress the NEED for CAUTION!!!!
Its a finite finicky resource...