Dash Stepper Motors & Blue LEDs

[Joe In Montana]

I got fooled into changing the stepper motors on my buddy's dually and while I was in there I had to put in blue LEDs for him.

"No sweat" I said.

Well - it's not a bad job - really!

It takes some patience, a lack of fear and some sneaky tricks (concerning the LEDs especially) to get it all together again once repaired.

Unfortunately I did NOT take pixs, but I can say that the steppers are really easy to remove the old and install the new - buy the kit and do it right!

The kit includes a needle-puller to take the indicator needles off the shafts of the existing steppers.

They pull right off - but treat them carefully since they are somewhat fragile. There ARE custom needle kits though - which I didn't need for this job.

The stepper motor kit I got was from Dr. Speedometer. I can recommend it heartily. Be sure to order enough motors, since the Transmission Temp gauge requires a motor too!

In the Dr. Speedometer kit will be some incandescent bulbs - very tiny ones - and these are the same that you cannot buy from GM for those other tiny lights in the various switches in the interior. Save them!

The LEDs were from Partsam. These are very nice and you'll get exactly the right number of LEDs to do the job, including one for the Transmission Temp gauge. It takes seven (7) motors for that dashboard cluster - don't forget.

BUY a solder-sucker - available at Radio Schlack - it you can find one still in business, that is. You MUST get rid of the solder by either wicking it away (this works, but is messy) or sucking it out of the heated joints.

The sucker is the best. Get a quality one! You can use it a few more times in your life.

The LEDs are harder. NOT the installation - but figuring out the polarity of the places where the old incandescent bulbs lived.

Incandescent bulbs don't require polarity considerations, but LEDs DO!

I left the long legs on the LEDs to make them easier to work with --- and just temporarily spot-soldered them to the unit and then plugged it into the wiring harness. The ones that didn't light up --- were in backwards.

You can't really hurt an LED by installing it backwards - other than the fact that it won't light up. The longest leg is the POSITIVE (+) one. Don't trim them short until you know for sure where they go!

I used a hemostat to hold onto the positive (+) leg of the LED until I trimmed it to correct length. Marking pens won't do it. I know of what I'm saying here.

Just swap the legs - (shortening them now as you know which is which) - so they fit very close to the printed circuit board.

Tools you'll need:

1. 30 Watt soldering iron --- NOT A BIG CLUNKY WELLER 3-SPEED GUN!
2. Solder Sucker
3. 50/50 or 60/40 solder (Doctor Transmission includes this!)
4. Rosin flux (keep 'tinning' the tip of the iron)
5. a CLEAN work station.
6. Good lighting - especially if you're old.

To access the speedo cluster, first take the trim/reveal off the front of the dash - just pull it gently with your fingers, starting at the top over the cluster and working your way around the cluster.

This is a plastic press-pin fit and they will come out cleanly if you don't get froggy and use a tool like a screwdriver or pry bar. Use your fingers.

There is sometimes Velcro holding the edges tight - watch for that.

The cluster will next come out with (about) four (4) screws.

Once the screws are out, then reach behind it before you try to pull it too far out, and unplug the male connex by pinching it (it's hard!) and pull it straight out.

There may be another connection - look around!

Installation, as they say --- is reverse of the removal.

The first cluster's a little hard* - but the learning curve is almost flat - and if you do the first one of these - you'll be the neighborhood Mister Wizard.

(* maybe it's just a lot of extreme concentration - but it really is easy!)

I hope this helps. It's just nuts-n-bolts.









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[Fordum]

Nice write-up.
Couple of points....
It looks like the LEDs you used were the surface mount type with leads soldered on by the company that sold them to you. Most all LEDs have some kind of mark to indicate which side is which besides the leads. Regular T5 LEDs have a flat side on the base that shows the negative side. Not sure what yours used, but there had to be something that they did not mention. The longer lead is standard for the industry, so there should be a second indicator also.
Regular LEDs Must have a resistor in series when hooked to an unlimited power supply otherwise they will burn up almost instantly. A lot of the kits that have replacement LEDs include a resistor that has to be soldered in series for them to work.
Since yours did not include them, they have either a resistor or a current regulated power supply onboard each LED. That makes it a lot easier, but not all kits are the same, and I don't want anyone to throw away the resistors if they buy a kit that needs them.

Also, since hooking these up backwards did not hurt them, they obviously have reverse polarity protection. But "raw" LEDs don't. you can blow a regular LED by hooking it up backwards to more than about 5 or 6 volts. Been there, done that.

As for the solder, 60/40 is the best, but 50/50 will work. Just be careful. Rosin core solder is the easiest to use, but there is also acid core solder out there. And most 50/50 solder that has a core is acid core. Using acid core will destroy the whole cluster.
Its so bad, if the soldering iron tip has been used with acid core before, it should be replaced, not just cleaned. The acid will hide in the tip even after its been cleaned, and will ruin what you are trying to fix.

If that sounds a little drastic, I once had to tell a company that their large, $5,000 (used) circuit board not repairable because the soldering iron tip that they had used to replace a simple capacitor before I got there was contaminated with acid core flux.
They assured me that it had been cleaned and re-tinned with rosin core, but it did not matter, the board was ruined.
Had it been a regular single sided board, or maybe even a double sided one, I might have saved it. But it was a multilevel board with foil traces inside the board its self, and the green corrosion was crawling everywhere.

I'm glad you wrote up this report. I was scheduled to do a stepper motor replacement on the dash of a big Kodiak wrecker, and had intended to write up the process. But at the last minute they went with a replacement board instead of ordering the kit. Even though I was going to do the job no charge.
Given the relative ease of doing the replacement, there is little sense for anyone here with normal skills to pay the price to send a board off. Maybe your report will help folks feel confident to tackle it.

 

[Joe In Montana]

I, fortunately had lost my soldering iron and so, buying a new one just for things like this - it was a virgin. Thanks for the heads up about irons used with acid core solder and/or acid based flux. Those are for plumbing, not electronics projects.

A 30 Watt iron is also too small for any plumbing unless it's in Barbie's Play Mansion....., but it helps to say that as a warning. Thanks again.

Try as I might, I looked for an indicator as to the polarity of the LEDs

All I could find was that one leg was longer than the other and used that as the (+) leg. I figure in hindsight that they sent these out as idiot proof and by saying that, I suggest that these be bought from the source I stated. I am not shilling for that company.

There are no hints about correct polarity on the board face, again probably because the OE bulbs dont care since they work either way.

LEDs DO care however, even though nothing untoward happened to them and none of the smoke leaked out of them by temporarily soldering them in, in either direction to test their ultimate and correct position.

I made no changes to the board as to a resistor. The kit said nothing about one, so it never bothered me. The LEDs are dimmable, perhaps that isn't mentioned --- but they are.

One other small point is that the stepper motor shafts and the relationship to where to put the needles is ...... you cannot screw it up unless you break a needle. They go on and you just turn (gently) the needle to point to the null point - or the lowest value for that particular gauge.

A NOTE HERE..... this null position is reset-able if you miss the mark. They sweep their whole travel when you energize them every time you start the vehicle - at least these did - but I only imagine they all do that. Just turn them to where you want them to start.

This kinda blew my mind... but never let anyone know that you are amazed by something like this. It keeps the Luddites in their place - respecting you as being obviously smarter then they are.

The stepper motors will start where you left them when you turn the key on the first time. The shafts can also turn 360 degrees and there is no 'stop' in them to index a zero-position.

It ain't rocket surgery....... it just looks like it!

One note about personal hygiene here: It goes without saying that your fingers have been washed - make that scrubbed clean ..... right? Human grease will contaminate the needles if they are painted.

(that needle paint is fragile, so handle them carefully and a minimum number of times)

Keep your clean or greasy fingers off the cluster face. I am sure that any cleaners you might try to remove your fingerprints will also remove the indicator faces too.

That part about the relationship of pointing the needles in the correct rotation on the motor shafts caused me some grief thinking I was somehow doing something wrong. It was a mistake to worry as the motors figured it out all by themselves. I thought there was some instruction I was missing.

"Why change out all the stepper motors?" you might ask. Because if one is screwed up, the others are right behind. Do them all the first time and save the grief of diving into the dashboard a second or even third time.

I agree that you can or should do your own repairs. That said: leave self-brain surgery or nuclear fuel rod replacement to someone else, but dashboard work is do-able by cavemen.

The standard legal boilerplate (yadda, yadda) has to be stated here about good shop rules:

So let it be known that wearing appropriate safety gear (chainsaw chaps, hard hat, welding gloves and radiation badges)..... all apply here.
Don't test the iron temperature with your tongue
Don't poke out an eye, even accidentally
Keep your fingers and other body extremities away from- and out of- moving parts.
There may be other rules.​

I think the site lawyers will see I have covered them from liability.