Friday, July 15, 2016

Fixing the squealing auto-tuner motors in the Kenwood TS-450

Note:
If you own a Kenwood TS-450 - or perhaps any other radio - and the motors squeal when the auto-tuner activates, DO NOT ignore it:  If/when the motors seize, they will burn out! 

This year I was setting up one of the club's Kenwood TS-450s in preparation for ARRL Field Day:  We had already set up the tents the night before and I was now laying out the radios.  Since it was morning - at an altitude of over 8000 feet (approx. 2440 meters) ASL, it was quite chilly on this late-June morning.
Figure 1:
The TS-450 with the tuner in need of attention.

Having connected the radio to the tri-band Yagi assigned to it I turned it on and heard a brief squealing sound emanate from the radio.  Suspecting that I was hearing the sound of a dry motor in the TS-450's auto-tuner, I changed bands - which caused the radio to re-tune - and heard even more squealing.

At this point it is worth noting the importance of this observation.  Since it was rather cold, whatever sparse lubricant was present in the radio was going to have less effect on its bushings, but it did indicate that the motor(s) in the tuner were in need of lubrication.  If the motors in the tuner get too "dry", they will seize up and then burn out as the tuner's "smarts" have no real way of knowing if the motor is stuck, applying power to them until a time-out occurs and when this happens, the user will likely retry a couple times.  Normally, the motors draw something in the 40-60 mA range when operating, but stalled, this can increase to well over half an amp, explaining how the motor can be damaged rather quickly - either by burning up the brushes, overheating the rotor windings, or a combination of both.

The reason why I was familiar with this problem is because several years ago a friend brought in a TS-450SAT in which the auto-tuner had failed.  In disassembling it, we quickly determined that one of the motors driving the tuning capacitor had seized and now measured open-circuit.  Having nothing to lose the motor was disassembled, but it was clear that the damage was more extensive:  While the brushes were somewhat burned - and could have been likely been burnished - and at least one of the rotor windings was open.

We soon discovered that (at the time, at least) a spare motor was not available from the radio manufacturer and that there were no recommendations for alternates to be found on the GoogleWeb:  We think that we did, finally, find a substitute and if this turns out to be successful, I'll be sure to write a post about it.

Not wanting to have this same fate befall the motors in this radio's tuner, I retrieved the radios (the club actually owns two TS-450SATs) after Field Day and took them into the shop to be worked on.  The (approximate) procedure for re-lubricating the motors is as follows, but first, a few weasel words.

Figure 2:
Cover over the low-pass filter, accessible after removing
the top cover of the radio.
Click on the image for a larger version.
Warning:
  • This is sensitive and delicate electronic equipment:  DO NOT attempt to service it unless you have a familiarity with electronics and servicing techniques.
  • There is a real chance that - by accident or otherwise - the tuner/electronics/radio may be damaged/destroyed:  YOU are entirely responsible for determining if the procedure that follows is within your abilities.
  • Although there are low voltages involved, there is still some risk.
  • Remember that your situation may not be completely identical to this one and that some/all of the steps described may not apply to you.
  • You have been warned!
Removing the tuner module:

First, disconnect the radio from its power source, its accessories and the antenna.  Next, lay out a clean, well-lit work area and locate several small containers in which to place screws and various items.

Taking off the top and bottom covers of the radio - noting which color and type of screws go where - also remove the the internal cover that shields the low-pass filter compartment next to the antenna connector as depicted in Figure 2.
Figure 3:
 Coaxial cables connecting the tuner and low-pass.  Note
that the "front" cable has a piece of white heat shrink
tubing on it.
Click on the image for a larger version.

With this cover off, disconnect the two coaxial cables (see Figure 3) that connect from the tuner to the low-pass board.  Note that the cable to the front has a piece of white shrink tubing, marking it:  If it does not, mark that cable now.

 Also connecting the tuner and low-pass board, there is another multi-wire connector nearer the front:  Gently remove this connector, unplugging it from the low-pass board.  Also carefully unplug the flat ribbon cable that connects from the gap in the middle of the tuner module and goes to the front of the radio, observing how it is routed through the bracket on the front of the tuner module.

With the cables disconnected, the tuner unit may now be removed.

Figure 4:
 Showing the two screws along the bottom edge of the tuner.
There is one more screw near the front of the tuner which
would be in the upper-left corner of this picture, on the
top of the tuner.
Also note the white, flat ribbon cable along the top of the
tuner from the front and how it is routed under
the metal bracket with the potentiometers.
Click on the image for a larger version.
Along the right side of the radio (the front facing you) near the bottom of the main deck there are two screws (Figure 4) that should be removed and a third on the top of the tuner module, in the corner, near-ish the front as depicted in Figure 5.  Make sure that you note the style of screws that were removed and from where.

Carefully remove the tuner assembly, noting the orientation in which it was mounted.

With the tuner removed from the radio, carefully unplug the cable that goes the front of the tuner, plugging into a socket next to the flat ribbon cable mentioned above and shown in Figure 11.

Now remove its top and bottom covers, again noting the type of screws (probably the same as those holding the tuner in the radio) and setting them carefully aside.

Lubricating the motors' bushings:
Figure 5:
The location of the front screw holding the tuner in place.

There is a decision to be made at this point.  It is most likely that the "driest" motor bushings are those at the "front" (shaft end) of the motor - but it is also may be that both the front and rear bushings will need to be lubricated, in which case the motor will need to be removed and partially disassembled.

The first, safe assumption is that the front bushing is the culprit as it is not only the most exposed to the atmosphere, but it also gets exerted on it the most off-axis stress when coupling to the worm gear.  It is possible - with the aid of a hypodermic needle or using a small screwdriver or piece of wire suspending a drop of lubricant to work it into the bushing at the front of the motor without further disassembly, with the job of getting to the left-hand motor (the one marked with "L" on the green circuit board) being a bit more difficult.

Figure 6:
 A recommended, long-lasting lubricant to be used.  If this
is not available, use only a good-quality, light oil such as
sewing machine oil:  DO NOT use a generic "3-in-1",
motor, or a "household" of oil.
Click on the image for a larger version.
Now, unplug the multi-conductor cable - the one in the connector next to the one from which the flat ribbon cable was removed earlier:  This cable connects the two motors and potentiometers to the internals of the tuner board.

With the connector from the motors and position-sensing potentiometers now removed, it is also possible to power-up each motor, independently by applying voltage (6-12 volts - preferably from a power supply with a 1 amp current limit) to the soldered connections on circuit boards (marked "L" and "R") directly.  Doing so will cause the motor to operate - but observe carefully that when this is done, the motor can hit the hard stop of the potentiometers in an approximately half-meshed state in either direction:  In other words, the range of motion of the potentiometers goes from approximately half-meshed, continues clockwise (as viewed from the shaft end) through fully-meshed, un-meshed, and then half-meshed.  As soon as the motor hits the potentiometer stop, you must remove the power from the motor immediately.


Figure 7:
 The potentiometer board and 4 (removed) screws.  Note
that the potentiometers are connected to the board only by
their terminals:  Avoid bending/flexing them by
their leads.
IMPORTANT:  If you remove this board you will
have to recalibrate the potentiometers to the
proper capacitor position when reinstalling.  This
procedure is described later on in this posting.
Click on the image for a larger version.
When powering the motor(s) in this way, they may squeal - but note that how well what residual lubrication works will be somewhat dependent on temperature.  For re-lubricating the motor I would recommend "Super Lube", a PTFE (Teflon (tm)) based lubricant that is readily available from some auto parts stores or on Amazon:  This lubricant will not dry out and it attracts minimal dust and it has been used successfully by the author to "un-stick" quite a few galled/damaged shafts with good, long-lasting results.  If you do not have access to this lubricant or do not wish to get some, it is recommended that high-quality light sewing-machine oil be used:  Whatever you choose, DO NOT use everyday "3-in-1", motor or "Household" oil as this will fairly quickly dry out and get gummy!

Figure8:
Removing the motor assembly from the tuner.  This picture
shows two screws at the bottom edge of the plate holding
the motors.  Note that the screws are slightly
offset, under the circuit boards which means that the
screwdriver shaft will be at a slight angle which means that
you will need to take care when reinserting them to make
sure that they do not go in at an angle and get cross-
threaded.
There are two similar screws on the same plate along
its top edge that must also be removed.
Click on the image for a larger version.
To lubricate the motors in-situ (e.g. without further disassembly) set the tuner on end with the green circuit boards at the end of the motors facing down.  Now put a small drop of oil on the end of a small screwdriver or wire (such as a straightened paper clip) and touch the shaft between the plastic worm gear and the body of the motor:  Surface tension should cause the drop of oil to run down the shaft and into the motor.  Using the same screwdriver/wire, gently nudge the worm gear up and down within the limits of end-play to help work the drop of oil into the bushing at the end of the motor.  If the oil immediately disappears or you aren't absolutely certain that any has gone in, add another drop or two in the same manner as above, moving the shaft up and down to help disperse it.  Once you are satisfied that some lubricant has made its way into the motor, wick up the excess with a bit of paper towel or tissue.

If it is not practical to access the end of the left-hand motor (the one with the "L") you may need to remove the assembly from the end of the tuner.

Additional parts that might warrant lubrication:

It is possible that other parts within the capacitors' drive trains are also in need of lubricant.  If you suspect this to be the case, check the following:
  • The ends of the worm/reduction gears.  Where the ends of the plastic shafts protrude through holes punched in the metal one can put a small drop of lubricant.
  • The bushings of the variable capacitors.  These are rather tight, by nature, but it is possible that the lubrication within is drying out.  To work additional lubricant into these heat the (metal!) bushings with a soldering iron to get them fairly hot (e.g. boiling water temperature) and then while still at an elevated temperature, put some lubricant on the shaft at each end that it emerges from the bushing:  The heat will cause the lubricant to become less viscous and as it cools, some of it will be wicked into the bushing.
  • In each case, above, make sure that one wicks up excess lubricant with a paper towel or tissue.

Removing the motor and potentiometer assemblies:

IMPORTANT:  If you remove either potentiometer - even momentarily - you will have to recalibrate the potentiometer setting to the physical position of the tuning capacitor:  The procedure for doing this is described farther down this page.

First, remove the potentiometer bracket using the four screws along the bottom edge - two per potentiometer - just below the pots as depicted in Figure 7.

When this is done the motor and potentiometer assembly may be carefully pulled out.  Note that the potentiometer and motor assemblies are still connected via their wires, so be careful not to stress or break them.

Figure 9:
Lubricating the end of the motor shaft after the plate has
been removed:  After working the oil into the shaft by
spinning/powering it and moving it up and down,
wick up the excess oil with a paper towel or tissue.
Click on the image for a larger version.
Using a very small Philips (tm) type screwdriver, remove the two screws on the plate as indicated in Figure 8 along with two similar screws on the same plate on the other side of the motor:  Note the style of these four screws as you remove them and carefully set them aside.

Now, you have easy access to the worm gears and ends of the motor shafts which may be lubricated as depicted in Figure 7.  Again, the small puddle of oil can be worked into the end of the shaft by spinning it with one's fingers and gently moving pulling the shaft up and down, taking advantage of the small amount of end-play.  Once you are satisfied that a reasonable amount of oil has worked into the shaft - often evidenced by the fact that they "feel" smoother and to not squeal when spun by finger or when powered up - mop up excess using a tissue or paper towel.

Finally, do not forget to lubricate both motors - even if only one was making noise!

At this point again apply voltage (6-12 volts) to each motor, one-at-a-time and allow it to run - the shaft facing upwards - for a minute or two - to work the lubrication in.  When free-running, each motor should draw between 30 and 50 milliamps.  Also listen to the motor to determine if it sounds quiet and free of rattle or squealing:  If the motor makes excess noise and/or the current is significantly higher than 50 milliamps it may need to have its "other" bushing lubricated - or it may have already sustained damage.

Lubricating the bushing on the "brush" end of the motor:

Warning:  

It is recommended that you do this step only if the motor continues to make noise after working lubrication of known-good quality into the shaft end of the motor as noted above.
Disassembling and reassembling the motor is a bit tricky and requires attention to detail and it is possible that the motor can be damaged/destroyed by performing this procedure without due care!
If you wish to continue and disassemble the motor further, you are doing so with the presumption that you have good mechanical skills and some experience at doing this.  Furthermore, you undertake this task entirely at your own risk!

Unfortunately, the "other" end of the motor shaft is not accessible without partially disassembling the motor.  As noted above, doing this task involves care, observation and careful attention to detail!  It is also recommended that only one motor be worked on at a time.
Figure 10: 
Removing the metal end cap from the motor.  This is necessary
ONLY if you have determined that the motor bushing opposite
the shaft end is dry as well.
Warning:  Disassembling the motor requires good mechanical
skills to do so without damaging it and should be undertaken
ONLY if you feel confident in doing so.  If done improperly,
the motor can be damaged/destroyed!
Click on the image for a larger version.

For this task, the first thing to do is to mark the motor closest to the "L" or "R" indication on the circuit board:  Making a scratch on the motor case is recommended as an ink marking may be easily rubbed off in handling.  Now, unsolder the circuit board from the end of the motor and set it aside. Now remove the motor from the bracket using the two, short screws - which should be very carefully set aside -

Using a very thin blade - of a knife or screwdriver - work it between the metal end cap and the white tab on the side of the motor.  This cap snaps into a slight groove in the main motor housing and should pop off fairly easily.

With the metal cap removed, carefully work the blade under the white plastic tab and the body of the motor, working it up to form a slight gap.  Now, while spinning the shaft back-and-forth, carefully work the plastic motor end-cap up and off the end of the motor shaft.

At this point look for a small, white plastic cap with a hole in it the size of the motor shaft:  Usually it will still be on the shaft of the motor itself, next to the armature, but sometimes it will remain in the end-cap, under the brushes.  If the latter has occurred, carefully slide it out from underneath the brushes and put it on the motor shaft with the slight ridge oriented to the inside (toward the windings) of the motor, toward the armature:  This ridge helps space and insulate the armature.

Now, using a small screwdriver or wire as an aid, place a very small drop of oil inside the bushing in the plastic end-cap.  Since it is almost impossible not to get a bit of oil on the brushes, carefully use a bit of tissue or paper towel to wick away excess outside the bushing and on the brushes.

Look at the brushes very carefully:  They should be straight, overlapping and almost touching in the center where the shaft goes through.  If they are not and/or are slightly bent, using a small pair of tweezers, very carefully straighten them out:  The idea here is that when the motor is reassembled, the brushes should gently touch the armature.  Note that these brushes are split and have two "leaves".

Now comes the tricky part and where damage to the motor is most likely:  Reinstalling the end cap.

Look at the plastic end cap and note that there are two slots:  These are used to move the brushes away from the armature when it is being assembled, and to do this a small tool - made of, say, #22 wire or a bent paper clip, must be constructed.  First, bend a length of wire in a square-cornered "U" shape so that it can slip easily into both slots, protruding in only a few millimeters as to be able to move the brushes.  The idea here is to insert this tool into the slot as far clockwise as possible (viewed from the end of the cap) and then once it is inserted, rotate it counter-clockwise to move the brushes out of the way while simultaneously putting the plastic cover over the end of the motor.  Doing may be made easier by clamping the motor housing gently in a vise to hold it secure.

If all goes well the plastic cap should seat into its original position and the motor shaft should turn easily.  If the plastic cap does not want to easily go on straight and/or the motor shaft does not spin smoothly and easily once the cap is reinstalled and leveled, carefully remove it - inspect the brushes and, in necessary, use tweezers to very carefully straighten them out, and try again.

Once you have gotten the plastic end cap into place, apply voltage to the motor again:  It should run.  If it is open, a brush is either hung up or bent out of place, but if the power supply indicates a short circuit (a very good reason to use a power supply limited to just an amp!) it is likely that the brushes are bent/out of position and the cap will need to be removed and the brushes inspected/adjusted.

If the motor runs and draws its expected 50-ish mA of current, orient the metal cap carefully over the solder terminals - aligning the square protrusions with the solder terminals in the plastic with the square holes in the cap and snap it back into place.  Again, check the motor to verify that it runs.

Soldering the motor back to the circuit board, take note of the mark that you made when removing it.  If you didn't happen to note which polarity of the motor went where, look very carefully at the white plastic square protrusions at the solder terminals you will notice that one is marked with a plus (+) sign:  The positive (+) side should go nearest the terminal marked with "L" on the left-hand motor and should go farthest away from the terminal marked with "R" on the right-hand motor.

Once the motor has been reassembled, re-mount it on the metal plate using the small, short screws:  It is strongly recommended that one use blue or purple "thread locker" compound:  Do not use "red" locking compound as it may prove to be difficult to remove, if necessary.

Recalibrating the potentiometers to the tuning capacitors'
 positions:

Now, using your fingers, spin the worm gear on the tuner's gear assembly so that each capacitor is precisely fully-meshed.  Note:  If you wish, you can do this after the next step, applying voltage (only 5-7 volts to achieve slower motion) to each motor as necessary.

With the motor(s) re-mounted to the motor mounting plate, reinstall the motor assembly/plate back on the tuner with all four screws, carefully engaging the worm gear:  Verify that the capacitors are still fully-meshed, briefly applying power to "fine tune" their position if necessary.  Using 5-7 volts instead of 12 volts for this step will cause the motor to move more slowly, making it easier to precisely set the capacitors to the "fully meshed" position.

Again, note that the two screws along the bottom edge of the motor plate are partially blocked by the circuit boards on the motor, causing the screwdriver shaft to be offset slightly:  Carefully start the screws to assure that they are straight and not cross-threading before torquing them with the screwdriver.

WARNING:

If you had to remove the potentiometers for any reason, it is very likely that their position - which provides indication of the physical setting of the capacitors to the radio's computer - got disturbed.
Again, it is necessary to make sure that the potentiometers are set to a certain value with respect to each capacitor being fully meshed in order to assure proper tuner operation and to prevent breakage of the potentiometer and stalling of the motor and burning it out.

It is now time to re-mount the potentiometer assembly.  Referring again to Figure 7, above, orient the potentiometers as shown:  If the wires are on the "wrong" side of the motors due to handling, they can be carefully re-routed through the gap between the two motor circuit boards.

On each potentiometer locate the "top" (upper-most) of the three terminals - that is, the one farthest away from the mounting bracket with the two screws - and the center terminal.  Using an ohmmeter, adjust each potentiometer for 1.75-1.85k across the top and center terminals.  Now, barely start the four screws that hold the pair of potentiometer brackets in place and, pushing the gears on the potentiometers onto the gear assembly of the tuner, re-check the reading on each with an ohmmeter.

If it is outside the range of 1.75-1.85k, there is enough room on the still-loose screws to move the potentiometer far enough away to disengage the gear:  Move the potentiometer one "gear tooth" at a time in this manner to get the reading as close to the 1.75-1.85k target as possible:  A value between 1.7 and 1.9k for a fully-meshed capacitor should be fine.  (One "tooth" of a potentiometer is equal to approximately 150-250 ohms of resistance.)

Once the two potentiometers are properly set with the above values, tighten the screws and re-check the potentiometer values before proceeding as they may shift slightly when maneuvering the screws.  It is worth noting that the holes on the potentiometer brackets are slotted, allowing each potentiometer to be moved slightly back-and-forth, individually, to "tweak" the values if desired.

It is not important that the potentiometers be set exactly for the above values as the total resistance values of these potentiometers can vary by 10% - it needs only be within the general range so that the radio's computer can read the analog voltage on the wiper leads of these potentiometers and then "pre-set" the capacitors' positions when one changes bands.  It should go without saying that once the radio is assembled, unless the potentiometers are exactly where they had been previously you may need to make the radio go through a tuning cycle.

Reassembling and reinstalling the tuner:
Figure 11:
The routing of the flat, white ribbon cable.

Now, reassemble the tuner, first putting the top and bottom covers on, noting that the cable connecting the potentiometers and motors goes outside of the top cover.  Now re-mount the tuner - avoiding trapping of any wires - into the radio using the three screws, plugging in the cable from the motors/potentiometer and the flat ribbon cable - routed as shown in Figure 11.  Now connect the two coaxial cables - the one with the piece of white shrink tubing on it going to the front - along with the multi-conductor cable that connected near the front corner of the low-pass board.


Final checkout:

The tuner/radio may now be tested:  Operate the tuner as normal and both capacitors should quietly adjust themselves as you change bands and a match be found when the button is pressed to cause it to tune.   After verifying that the tuner is operating normally, put the rest of the covers back on and enjoy the radio!

[End]

This page stolen from "ka7oei.blogspot.com".

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