If you are at this page you probably have a Polaris with a bad speedometer which means that you can't put it in 4 wheel drive and your reverse override doesn't work.
If this has happened to you, you probably ran it without a good battery - or with no battery at all: Read on to find out why you should never do that if you can help it!
There are at least two versions of speedometers used in the late 1990's and early 2000s - the one that, inside, looks like Figure 4 with "through-hole" components and a slightly newer version that largely uses surface-mount components. While both versions seem to have the same fate when used with a bad (or no) battery - and the "fix" is likely similar, I have not personally seen the newer surface-mount version, but you can find information on its repair near the bottom of this article as provided by one of the readers.
If you have successfully repaired one of these newer versions and are willing to share the specifics, I'd be happy to post it here. If you have a "dead" speedometer of the newer version and would likely me to take a crack at fixing it (absolutely no guarantees about success!) then feel free to contact me via comments, below.
Last year, a friend of mine had the battery go bad on his 1999 Polaris Sportsman 500 4-wheeler. Aside from the inconvenience of having to pull-start it, it seemed to work OK.
Soon, it was noticed that the speedometer had died and interestingly, a few other things quit working at the same time such as the ability to put it into four-wheel drive. When the battery was finally replaced the speedometer still
did not work so a he dug around in the internet and found that this is quite a common problem with that vintage of Polaris vehicles - and it seems to work out this way:
The charging system's voltage regulator on these vehicles are fairly simple, but they depend strongly on the presence of the battery to moderate the wildly pulsating DC coming out of the alternator/regulator system to maintain the average
voltage in the range of 13.5-14.2 volts or so. If the battery goes completely bad or is removed, the charging system goes haywire and the voltage can (apparently)
exceed 20 volts (and is probably higher)
and one can risk burning out the various indicator, marker and headlights.
Another fatality under this conditions seems to be the speedometer module itself!
What (probably) happens:
It's probably not
the high voltage that actually kills the speedometer: The voltage regulator circuit in the speedometer seems to be fairly robust, using high voltage (>=300 volt) transistors to withstand the voltage spikes that are endemic to any vehicle electrical system. What seems to kill these things is heat.
Let me explain.
The job of the voltage regulator circuit inside the speedometer is to assure that the voltage feeding the circuit inside doesn't exceed about 15 volts or so and from there, it is regulated down even lower by other circuitry for the computer that provides the odometer readings and (probably) the speedometer as well as having something to do with the reverse limiter designed to prevent you from accidentally driving backwards at a high speed and
the lockout/controls for the all-wheel drive switch. There are also several small light bulbs inside the speedometer that provide backlighting for the display at night and these, too, are protected from high voltage by the 15 volt regulator.
Under normal conditions the voltage on the vehicle's electrical system is around 14 volts or so and the regulator's job is to suppress spikes and brief excursions above that and in this mode, the regulator itself isn't doing much. If the voltage rises, however, it has to drop the excessive voltage and and a natural by-product of this is that it develops heat.
Apparently, quite a bit of it! In testing the speedometer after the repair I applied 20 volts to it and the main regulator transistor soon got too hot to touch: If this had been a hot, summer day with the transistor crammed inside the waterproof speedometer casing with no free air ventilation, it would have been much
So, with the bad battery and a subsequently malfunctioning charging system it is easily likely that the speedometer's regulator saw an average of 20-30 volts on its input. At some point the transistor overheated and eventually failed internally, shorting itself out. Fortunately, the majority of the circuits in the speedometer seemed to survive this since once the regulator itself had quit, all power feeding the rest of the circuit was lost completely, preventing further damage.
While a new speedometer is available as a replacement part, it will cost you several hundred dollars, new!
Fortunately, it may
be that you
can fix it!
The obligatory warnings, etc.
- Assume from the beginning that the speedometer is a total write-off and that you would have to replace it, anyway. This way, if you can fix it, you will be money ahead - but if you can't, you haven't lost anything more!
- Before you start, read this entire posting so that you'll know what you are in for!
- Repair of the speedometer requires some knowledge of electronics and board-level electrical components.
- Repair also requires good unsoldering and soldering skills and equipment - and a soldering "gun" doesn't count. If you don't have the proper tools and experience in the replacement and installation of individual, through-hole components, do not even attempt this!
- The speedometer is part of the electrical system of the vehicle and as such, it is possible that its malfunction - possibly due to a failed repair - could cause additional damage to other components.
- No, I won't repair your speedometer as with shipping, time, "hassle factor" and labor, I'd have to charge a sizable percentage of the cost of a new one. I suggest that you find someone versed in electronics to help you out if you need to do so.
- I know ONLY about the speedometers on Polaris Sportsman 500's for the years 1999 and 2000: If you ask me about speedometers for any other make, year or model, I can't help you! (They may be the same - they may not - I don't know.)
- You do this repair at your own risk! Do not get mad at me if you blow something up, set fire to your four-wheeler or cause all of your dog's hair to fall out!
How to do it
Remove the speedometer:
- Again, there seems to be a (newer?) version of the speedometer with more surface-mount parts that can suffer the same fate. While I have not seen one of these, personally, one of the readers has provided information about his successful repair: With his permission, I have posted this update near the end of this article.
The first step is to remove the speedometer from the vehicle. It's a bit of a pain, but it's not terribly difficult to do as it is almost the same procedure as would be followed for replacing the headlight.
Inside the housing that covers the headlight you'll find two connectors that snap into the speedometer, held in place with release tabs, as well as two nuts that hold the bracket in place: Note how these go together before
taking them off - make a drawing and/or take a picture before you take everything off if you aren't sure.
Open the speedometer:
Place the speedometer face down on a clean, un-cluttered work area on a surface that you don't mind scratching: It's recommended that you put a rag or old towel between the face of the speedometer and the work surface.
Now, notice the soft, aluminum ring around its perimeter: This holds the clear, plastic cover to the body of the speedometer by virtue of crimping between those two pieces a rubber gasket.
Wearing leather gloves
to prevent being stabbed during this step, use a medium-sized blade screwdriver - preferably one that is somewhat worn out with rounded edges - and slide it between the aluminum ring and the plastic body of the speedometer on the back side, prying the ring open as you go along, straightening it out. With a bit of practice you can firmly slide the screwdriver along the perimeter and straighten out that soft, aluminum ring and you will probably have to go around several times to do the job.
|Figure 1: |
The soft, black, aluminum ring around the perimeter of the speedometer that holds the faceplate to the body. Carefully pry this straight.
(This picture was taken after I'd already opened and repaired it - and partially closed it again.)
Click on the image for a larger version.
Once you get 75-90% of the backside of the ring straightened out, you'll be able to pop the ring off the front: Set it aside. With the ring removed you should be able to use your fingernails and pry the front, clear cover from the body of the speedometer.
Be careful with the black plastic rod under the push button
, noting carefully how it is installed and taking care that it doesn't fly off somewhere!
Once you have the cover off, set it aside with the black, plastic rod laying inside the cover.
Remove the needle:
This is sort of tricky and it is possible to ruin the speedometer with this step: Since you have already declared the speedometer to be a total loss, you shouldn't feel too bad if you do.
First, note how far the needle is pushed on to the spindle: You'll want to remember this when putting it back on.
If you have very strong fingernails
, try pulling the needle straight
off the speedometer, but whatever you do, apply tensions EVENLY
- that is, pull straight out
on the needle as you do not
want to bend the spindle! When you pull on the needle make sure that the speedometer is on the workbench with padding on it because if it comes off suddenly, you don't want to slam your hand or the speedometer into the workbench and break something!
If you can't remove the needle with our fingers, you'll need to apply a bit more force. Cut some pieces of paper or thin cardboard (such as from a cereal box)
so that you cover the entire face of the speedometer, but allow access to the needle and its spindle - this being done to prevent you from accidentally marking up the speedometer face.
Now, using two medium-size blade screwdrivers, pry the needle evenly
off the spindle using the paper/cardboard to prevent damaging the speedometer face: You may want to wrap a rag around the body of the speedometer and clamp it gently - but firmly - in a vise. Hopefully, the needle will come up without breaking anything else! If you do
break something else, save up for a new speedo!
Remove the speedometer module from the body:
Using a small screwdriver blade or, preferably, a similarly-sized and shaped piece of plastic, carefully pry up on the face of the speedometer. The face is actually printed on a piece of fairly heavy, self-adhesive plastic that is about as thick as a postcard - and it is this, not the actual body of the speedometer itself - that you want to pry up. It can be a bit tricky to get purchase on the speedometer face and you might bend into a hook a small piece of metal such as a paper clip to act as a tool.
|Figure 2: |
By carefully prying up the speedometer face's plastic, you can access the three screws that hold the module in the body. The other two screws are located 1/3rd of the way around, at approximately "10" and "40" MPH. If you can't get the needle off before this step, make sure that you move it out of the way when you pry up on the face plate so that you don't accidentally break it.
Click on the image for a larger version.
Start by prying up on the plastic face below and in the middle of the LCD odometer display, at the bottom of the speedometer and once you lift it a little bit, you will see underneath it a Philips type screw: Holding the speedometer face up with a small screwdriver, use another screwdriver to remove that screw.
There are two other screws, each located 1/3rd of the way around on either side: Remove those, too.
Now, the only thing holding the speedometer module inside the case is friction and the silicone used to seal around the wiring connector pins on the back. Using a small blade screwdriver, work your way around the perimeter of the inside of the speedometer, wedging gently between the outer body of the speedometer and the module itself, reaching down slightly past the face of the speedometer to do it. After going around several times, applying a bit of twisting and/or prying force, the module will hopefully break loose and gradually come out.
When it does this, the pins from the electrical connectors on the back will be pulled through the case and soon, you'll have the module separated from the case.
Removing the LCD and accessing the back of the circuit board for soldering:
- There are one or two cylinders with granules packed inside them in the case that contain moisture-absorbing compound. As you remove the body of the module, they may come out, or they may be (at least temporarily) stuck in place in their own crevice inside the module - but in any case, note where they originally sit. Take them out and place them in a "Zip-Lock" (tm) bag and suck out the air to protect them from additional moisture while you are working on the speedometer.
order to get access to the "solder" side of the circuit board you'll
need to remove the portion with the face plate, after you have removed
the needle. In so-doing, you'll also be removing the LCD odometer
display. It is recommended that you do this over a workbench covered by a rag or towel in case the fragile LCD falls out.
On the back side of the speedometer module (the "component" side of
the circuit board) you'll find four black screws that correspond
approximately with the four corners of the LCD display. Laying the
speedometer face-down on a piece of cloth
, remove these four screws:
The front faceplate portion will separate from the circuit board.
This front portion also retains the LCD in place and it may fall out. If it doesn't come out on its own, carefully remove it - noting the markings on the LCD and which way they were oriented with respect to the board.
|Figure 3: |
repaired board showing the LCD. Note the orientation of the writing on
the LCD with respect to the board. If you look carefully, you will
notice markings on the upper-left edge of the LCD which may be used to
indicate which way is up.
Toward the 2-o'clock position of the
speedometer board you can see the repair to the damaged trace. Because
the board is coated with a sticky conformal coating compound used for moisture protection it's
difficult to avoid discoloring when soldering due to the heat and flux.
Click on the image for a larger version.
The LCD's electrical connections to the
circuit board are made via two small strips of pink-ish conductive
rubber sandwiching darker rubber (often called "Zebra Strips")
and these usually stick to the LCD. If they are stuck to the board,
very carefully remove them, but if they are stuck to the LCD, don't
worry and leave them in place. Set the LCD and the rubber strips aside in a clean, dust-free
place such as a clean, dry food container. You may notice that the LCD itself has a part number printed on
it: Note its orientation so that you can reinstall it correctly.
You now have access to both sides of the circuit board.
Identifying the bad components:
Important note (again) about through-hole versus surface-mount versions:
The pictures and descriptions below assume a through-hole version of the speedometer. It would seem that a later model of this same speedometer uses surface-mount components for some of those that fail.
While I have not seen a surface mount version of this speedometer in person, one of the readers of this blog entry with a failed surface-mount version of the speedometer was sufficiently inspired to attempt a repair - and was successful!
With his kind permission, some details on the repair of a surface-mount version may be found at the bottom of this blog entry.
It seems that the one part that is sure to go is a large-ish power transistor, but there can be two components next to it that are also destroyed - and this damage may be evidenced by some burn marks on the circuit board: See Figure 4, below, for identification of these components.
|Figure 4: |
Location of the likely bad part(s). When I took this picture I had already replaced the TIP48 and the MPSA42 - but not the Zener diode. There have been reported instances where the parts have gotten so hot that the solder has melted and that they have simply fallen out: If this is the case with your speedometer, be sure to test the parts before reinstalling them or, if you don't have the facility to do that, simply replace them.
Click on the image for a larger version.
Even though only one or two of these components may be bad, I would recommend replacing all three
of them. These are:
- A TIP48 high-voltage NPN power transistor. This is the most likely component to be damaged and is a transistor with a metal tab. In Figure 4, above, the leads are, left to right, B-C-E. (The NTE equivalent is the NTE-198. Note that previously I'd inadvertently listed the '197, which was incorrect.)
- An MPSA42 high-voltage NPN low-power transistor. This is a small, black transistor located next to the TIP48. In Figure 4, the leads are C-B-E from top-to-bottom. (The NTE equivalent is the NTE-287.)
- A 1N5245 15 volt, 1/2 watt Zener diode. This is located next to the MPSA42 transistor and is a small, (usually) red/orange glass device on axial leads. In Figure 4, the "banded" end is the lower end. (The NTE equivalent could be the NTE-5024A or its 1-watt version, the NTE-145A.)
The only critical things about the two transistors are the fact that they are NPN devices rated for at least 300 volts to withstand the normal transients found in a vehicle electrical system. If you are unfamiliar with electronics I would suggest that you replace these with exact types which are readily available from Mouser Electronics or Digi-Key Electronics - or you can get cross-reference equivalents in the NTE family (noted above)
from MCM Electronics or even find a local distributor that carries the NTE parts.
If you are
familiar with electronic components:
- The TIP48 may be replaced with about any NPN bipolar transistor found on the "mains" side of an AC-powered switching power supply - such as a dead computer supply. Typically, these transistors are rated for more than 400 volts and are in a TO-220 style case - often with a plastic or insulated tab - which really doesn't matter in this application. Just make sure that it's rated for at least 300 volts and has the same pinout (B-C-E as viewed left-to-right with the leads facing down and the label facing you) as the original TIP48! Chances are this transistor will have a number that begins with "2SC" (or just "C") followed by 4 digits: Look up the device's data sheet online and verify that it is, in fact, a high-voltage NPN device. The one that I happened to used came from a junked VCR, was rated for 500 volts and happened to have a plastic tab rather than the metal tab of the original device.
- The MPSA42 is a high-voltage, low-power NPN transistor of the type typically used in video drivers for cathode-ray tubes on older TVs and suitable equivalents may be found on the small circuit board attached to the end of a CRT on a discarded television. I happened to have some ZTX458 transistors - devices that had equal or better voltage/current specs than the original - laying around from another project and used one of them. Just make sure that you take into account any differences in the pinout of the replacement transistor!
Replacing the components:
- I didn't have a 1N5245 1/2 watt, 15 volt Zener around, but I did have a 1N4744 Zener which is a somewhat beefier 1 watt version with the same voltage rating, so I used it.
- Unless you are experienced in component replacement and circuit board repair, I would not suggest you do this procedure at all!
- Use a temperature-controlled soldering iron. Too little heat, you'll damage the board trying to get the components off. Too much, you'll damage it that way, as well.
- Do NOT use a soldering gun for this repair work: If that's all that you
have, you really should not try it as you'll likely ruin the board!
- Using your phone or camera, take some close-up pictures of both sides of the board before you start as a possible aid in reassembly.
- You must have proper desoldering equipment. A vacuum-operated desoldering tool is the ideal, but "Solder Wick" (tm) or even a spring-loaded "solder sucker" or "desolder bulb" will work. If you don't have any of these it will be challenging to get the through-holes cleared to install the replacement components without tearing traces off the board.
- Both sides of the circuit board and most of the components are covered with a moisture resistant coating. This coating is slightly rubbery and when soldered, it gets discolored. Fortunately, you can "solder through" it although extra care should be taken to assure that the solder joints are clean and good. When you are done soldering, you can clean the flux with alcohol and a cotton swab, but the discoloration will probably remain. (If your solder uses water-based flux, make absolutely certain that you have removed it using clean water as many of these types of fluxes can slowly corrode connections.)
- When removing the old components (the two transistors and the Zener diode) it may be easiest to just clip them from the board first using small, sharp diagonal-cut pliers. This will remove the body of the device and allow each lead to be removed independently.
Using "solder-wick" or a vacuum desoldering device, remove the two transistors and the Zener Diode, noting the original orientation of each device. Make sure that you also clean out the holes through the board!
In my case, the heat of the original TIP48's destruction and its subsequent removal from the board actually damaged a trace so I had to repair it with a short piece of wire (I used #30 wire-wrap wire)
on the bottom-side (that's the short green wire visible in Figure 3) but it's likely that your damage won't be that severe.
After inspecting for damaged traces, install the new components. The notes above indicate which lead is which when replacing the two transistors and the diode.
Putting it back together:
|Figure 5: |
The newly-repaired speedometer. It shows a speed because I was injecting a signal on the back to simulate input from a wheel sensor.
If you look carefully you might note that the 10th's of a mile digit on the LCD is missing part of its top half: To fix it I had to take it apart again, clean the rubber pad ("zebra strip") the circuit board contacts and the LCD with some denatured alcohol and reassemble it to remove the mote of dust that prevented part of that particular digit from working properly.
Click on the image for a larger version.
As they say, "Assembly is the reverse of disassembly"!
A few comments:
- When putting the LCD back in place, it may be a good idea to wipe down the top and bottom edges of the rubber strips with an alcohol-wetted cotton swab, and this should also be done for all surfaces of the LCD itself and the metal contacts on the circuit board. Doing this will make sure that there aren't any dust particles, fibers or hair that may cause one or more of the LCD's segments to not work.
- The two rubber strips for the LCD just sit in place, on edge, in the LCD mount and the LCD goes on top of it. When mating the face of the speedometer back to the circuit board, make sure that you have re-installed the LCD right-side up and oriented properly (remember when you made note of the marks on the LCD?) so that you don't accidentally crush and break it when putting the speedometer face back into place. Make sure that the four black screws are tightened firmly - but not so tight that you crack the plastic.
- Before sealing everything up, carefully remove obvious fingerprints from the LCD (using a cotton swab) and the inside of the face plate as well as the speedometer.
- If you have a bench-type power supply capable of 12 volts at about 600 milliamps, you can do some preliminary testing of the speedometer by +12 volts to pin "A" and the ground to pin "B". If all goes well, the lights will turn on and you'll see the odometer displaying numbers. See below for a description if the pinout.
- If you have applied power and everything looks OK, gently push the needle partway onto the spindle, aligning it with "0". With the power applied, move the needle up scale (say, to 20-40 miles-per-hour) and watch it go back down to zero: If it stops slightly off zero (it may take 10-15 seconds to settle when the unit is powered up) then pull the pointer off and re-align it, re-doing the above steps again until you get it to land on zero.
- If you can't power up the speedometer, line the pointer up with zero and then move it up-scale to 20 or so. After 5-10 minutes (yes, it may take that long to slowly move back!) look again to see where it is pointing: If it isn't at zero, remove and re-align the pointer and try it again.
- Once you are satisfied that the pointer is correct, firmly push it in on the spindle as far as you noted that it had been pushed before you'd removed it. Move the needle up-scale by hand again and verify that it will (slowly) move down, indicating that it isn't binding anywhere. If the pointer isn't pushed in far enough it can jam on the inside of the faceplate.
- In the case you may have noted one or two small cylinders with granules inside them that are either still in place, or had previously fallen out and it was recommended that they be put in a sealed storage bag. These are moisture absorbers and they sit in a slight recess one one side of the case. It is recommended that these be reinstalled
- When you put the speedometer module back into the case make sure that you move the needle out of the way when you pry up on edges of the speedometer face to reinstall the three screws.
- Strongly recommended to maintain waterproofing: Apply a thin layer of silicone grease to the gasket that goes between the body of the speedometer and the clear front plate, taking care not to get it on the face plate where you can see it. (Just wipe the grease off if you do get it on the display or the back side of the clear cover.) You may use silicone-based "Plumber's Grease" available at practically any hardware/home improvement store. Do not use a petroleum-based grease for this!
- When putting the face plate back on, remember to re-install the black push-rod that operates the button!
- Test-fit the face plate to make sure that you pushed the needle on far enough and is not rubbing on the inside face plate.
- Slide the aluminum ring back into place. With the speedometer face-down in a cloth (preferably a gap to accommodate the button on the front panel) use a piece of wood to re-crimp the aluminum ring to attach the face plate to the body. You'll probably have to go around the perimeter several times to get it tight.
Comments about pin-out and testing:
Note: If you do an internet search, you should be able to locate some online drawings showing the pinouts of the speedometer's connectors. If you do this testing, you would do so before reinstalling it in the case.
- Squirt a dab of silicone grease (but not silicone seal!) this in each of the electrical connectors on the back side: This will help prevent ingress of moisture as well as prevent possible corrosion of the electrical connectors. Again, "Plumber's Grease" or the sort used to lubricate "O" rings is this same sort of grease and will work fine and this is available anywhere you can buy plumbing supplies and parts - including big-box home-improvement stores like "Lowes-Depot." Remember: It is not recommended that one use "normal" petroleum grease (e.g. axle grease, Vaseline (tm)) as this will degrade the plastic and connectors!
With the speedometer facing down, orient it so that the 6 pins of the larger connector are toward the top running horizontally and that the 3 pins of the smaller connector (the one for the wheel sensor)
is to the right of it with its pins running vertically.
For the large connector, pin "A" is on the left and they are designated on available drawings as A-F, left-to-right. For the 3-pin connector they are A-C starting from the top and working down.
Applying voltage to these pins using a regulated, current-limited
power supply set to 12-15 volts at a maximum current of 600 milliamps to 1 amp, you should be able to power up the speedometer.
- Do NOT power the speedometer being tested directly from a battery as that could supply virtually unlimited current in the event of an accidental short or fault.
- DO NOT connect the polarity backwards - even for an instant.
- If your current-limited power supply "sees" a dead short, remove power immediately and check for solder bridges around the components that were replaced.
If it works, the lights should come on and if you move the speedometer needle with your finger, up-scale, it should reset itself to zero much more quickly than it had with the power off. An additional test is that if you increase the voltage above 14-15 volts (but not above 20 volts!)
the lights will not
get any brighter - a sure sign that the regulator is now working properly. If you do this, now is the time to double-check that the needle points at zero.
If you are curious, you can apply a square wave signal from an audio generator (3-5 volts RMS) between pins B and C of the 3-pin connector and vary it from about 5 Hz to 200 Hz and you should see the speedometer go up with increasing frequency as you simulate, with your audio generator or "function generator", the input from the wheel sensor. Pin "C" is ground while pin "B" is the signal input.
The unit must be powered up in order for the speedometer - and odometer, for that matter - to indicate. If you do not have a piece of test equipment to generate such a signal, a "555" timer chip may be wired up (with the appropriate components)
to generate a variable frequency square wave train.
If all goes well, your speedometer, 4-wheel drive switch, "reverse override" button and odometer will now work properly again!
that there's no guarantee that it will be as waterproof as it was
before since you probably lack the special machine required to properly crimp
that aluminum ring down so it's probably best to keep it out of rain as
much as possible - a good practice, anyway!
I occasionally get asked a question via this blog's comment tool. Unless you include a return email address, you'll have to check back here to see if I've answered it as I won't be able to reply any other way.
Repairing the Surface-Mount version of the Speedometer
October, 2015 August 2016 October 2017 November 2018 the repaired speedometer is still working fine.
One of the readers (Mathias)
was inspired by this blog entry and decided to attempt a repair of the newer surface-mount version of this same speedometer. It is not known, exactly, over which model numbers and years this speedometer was in use (or if it still is!)
What follows below details the repair of a unit from a 2000 Polaris Sportsman 335. Again, unless you are familiar with work on small electronic components and have the appropriate tools to do so, please seek out someone who does have the the familiarity/tools before attempting a repair! You have been warned!
Used by permission of Mathias, this is a photograph of the surface-mount version found in a 2000 Polaris Sportsman 335. It is believed to be (more or less) the same circuitry as that shown in figure 4, above - but using more surface-mount components.
The thread of the related conversation - including a reference to the picture above - may be found in the comments below: Look for those related to user "Mathias999us".
Click on the image for a larger version.
Figure 6, above, shows the surface-mount version that seems to suffer the same fate when the unit is run without a battery to moderate the voltage. The above drawing is annotated with some clarifications added below:
- TIP48 - This is the same power transistor (through-hole) as used in the older version.
- "SMD marked 1Dt" - This is the same function as the MPSA42 used in the older version, except surface mount. The case marking of "1Dt" (assuming that the writing was deciphered correctly) is a bit ambiguous, but it refers to an NPN transistor. It is believed to be a BC846 transistor - a general-purposes NPN device that is rated for 65 volts.
- It should be noted that the MPSA42 is available in the same SMD footprint as the above and is known as the "PMBTA42". This may be a better choice than the BC846 in terms of being able to handle voltage spikes, should the Polaris be operated without a battery.
- "Unidentified diode" - There are two of these:
- The large one appears to be just a standard diode. If open/shorted, the surface-mount version of the 1N4003 (through 1N4007) should be fine.
- The small one is likely a surface-mount version of the Zener diode called out above - namely a 15 volt unit.
- Capacitors: These aren't marked in Figure 6, but they are the large, metal cans next to the TIP42.
- These are often damaged by the heat and voltage when the speedometer is run without a battery.
- If one/both of these capacitors look at all bulged or swollen, if it looks like their plastic labels have shrunk and split and/or if there is some sort of liquid coming out of them - either from the seam on the top or at the circuit board - they MUST be replaced!
- These are reportedly 470uF, 25 volt capacitors.
- Before removing them note which end of the capacitors are marked with the minus sign so that the new ones may be installed correctly.
This page stolen from ka7oei.blogspot.com