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Old 05-25-2009, 09:05 AM
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krek krek is offline
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Electronics Gurus - Help Me Dissect Circuit Board for Digital Gauge

Here's my plan... I want to use two digital gauges to add a voltsmeter and oil pressure to my early gauge panel where the idiot lights are.

This is the gauge:



And this is what it could potentially look like:



This is why the whole assembly won't fit in the stock location:



And this is where I assume I can "unsolder" the LED numbers and extend some wires between the circuit board and the numbers:





Is it possible to dissect and re-assemble the gauge? Am I on the right track?
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Old 05-25-2009, 10:40 AM
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Well, it certainly looks possible, but there could be problems. Spent the first 15 years of my adult life as an electronics tech, and was always playing around with things back then. The thing to remember, is that it is pretty hard to pull a DIP semiconductor like that without lots of heat. You could use wicking braid, or a vacuum de-soldering station, and still not get all the solder out. The best rule of thumb for desoldering components, is that the removal generally destroys the component due to too much heat. If it was a cheap, easily found component, and you don't mind replacing it, I would say go for it. Those are some pretty massive components and the actual led is far removed from the heat of desoldering, so it should be fine, but you could end up with non-working parts.


That said, if you got it out, and it still worked, then remote mounting the LED's should work fine as long as you only went a few inches. Beyond that, and all bets are off. Intensity on LED's is adjusted by pulsing the signal rapidly, and long runs might not work so well. If I was going to try it, I would try to source some replacement LED's, and pitch the originals. Looks like something you might be able to order from Radio Shack.
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Last edited by DAHoyle : 05-25-2009 at 11:05 AM.
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  #3  
Old 05-25-2009, 10:47 AM
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Cool idea

You should have no problem de-soldering that to make it work the way you want.
If you dont have one already, I reccomend the cheapo de-soldering iron from Radio Shack. Ive desoldered probably a million joints with one and dont think I ever damaged a thing with it.
They work surprisingly well for the price, dont let the price tag fool you.
The only caveat is to make sure you squeeze the little vacuum bulb BEFORE you touch the iron to the solder
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  #4  
Old 05-25-2009, 10:52 AM
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I always use desoldering braid to remove components, works alot better and easier than the bulb, disapates heat, and leaves a nice clean hole to solder your wire in.

I do alot of electronic projects/repairs on the side, I could tackle for you if you're not in a big rush. PM if interested.
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  #5  
Old 05-25-2009, 11:10 AM
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the problem with most soldering irons and desoldering irons is that they dont have a ground wire. the ac voltage creates some crazy noise that can fry components
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Old 05-25-2009, 11:28 AM
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Yep, I like solder wick. The vacuum desoldering tools work ok for a single joint, but unsoldering a DIP type component is hard. One possibility is to clip the leads very close to the board - get a pair of nippers specifically designed for close-cutting leads to circuit boards. It will be a fairly dainty tool, with small tips but large enough to fit in your hand.

<edit> You can try the above suggestion, but looking at the board, looks to me like you won't be able to get at each side of the LED/LQD. If you can buy another LED/LQD display (just the display part), you could cut the LED/LQD off and use the new parts fly-wired to the board. Or get two of these gauges, and cut the board off on one and clip the LED/LQD off on the other.

Source for replacement displays: Mouser electronics http://www.mouser.com/ or Digikey http://www.digikey.com/

Once you clip the LED from the board, there should be enough lead left to solder a fine solid wire to each stub. You need to be good with the iron though. I'd use maybe 24 or 26 bare copper wire and spaghetti tubing.

Once you clip the LED off the board, desoldering each of the pads one at a time will be easy with a vacuum tool.

Be sure to use a high quality low-wattage temperature controlled iron specifically meant for electronics work, and high quality solder.

hth!
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Last edited by tgreese : 05-25-2009 at 11:51 AM.
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Old 05-25-2009, 12:15 PM
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X3 on solder wick.

I like Mouser electronics for parts.

Huge catalog doesn't burn well, smolders for days
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Last edited by men in black : 05-25-2009 at 12:18 PM.
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Old 05-25-2009, 12:30 PM
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Quote:
Originally Posted by krek
Here's my plan... I want to use two digital gauges to add a voltsmeter and oil pressure to my early gauge panel where the idiot lights are.

<snip>

Is it possible to dissect and re-assemble the gauge? Am I on the right track?
My first question is that the guts from an aux gauge, and do you have the correct sending units for that display?

I'm no electronics guru, but I'll give it a shot.

The circuit board is what makes the correct number display. I guess you could remove the display from the circuit board and re-solder a wire to each pin on the display and to the board, so you could mount the display part in the dash and mount the circuit board a few inches away somewhere behind the dash. But it would still have to be wired to the circuit board or it would only (at best) display a nice bright zero or three constantly flickering eights. At worst, immediately fry or blow a fuse or something.

Is that what you were asking?
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Old 05-25-2009, 01:09 PM
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Quote:
Originally Posted by men in black
Huge catalog doesn't burn well, smolders for days


yea I bought 2 dollars worth of parts and they sent me 2 catalogs lol
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Old 05-25-2009, 03:23 PM
Joe Guilbeau Joe Guilbeau is offline
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Solder-Wick will get the solder out, but heat soak will be a problem unless you are quick about it.

Use the Solder-Wick to get most of the solder out of the thru plated hole on the circuit board, then you can use a pick with a soldering iron to pull the pin away from the plating on the hole to center it without heating up the spot too much.

How many leads do you have to de-solder? Looks to me at least 10 and perhaps more?

Now you have the problem of remote mounting the LED display and securing all of those wires onto the unsupported leads...that will be interesting.

I've put solar cell arrays on spacecraft, done down hole soldering on oil field tool with high temp soldering, done NASA certified soldering on microwave components that are 6-thousands of an inch long and 3-thousands of an inch wide (and smaller).

With the right tools it will be possible, some thoughts on how to ensure that vibration on your remote soldered LED Display will be worthwhile. Get a breadboard with traces pn the through hole patterns and 0.1" centers (from what I can see on the images).

This way, you can re-solder the LED display into the breadboard and connect the now divorced circuit to the LED Display with 20AWG wiring.

Use Loktite Tak Pak (LOCTITE 382 Ultra Performance TAK PAK Instant Adhesive 20grKit ) to secure the wires to both breadboard and circuit board so that the vibration will not cause solder joint failures.

Have a steady hand.
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  #11  
Old 05-25-2009, 04:29 PM
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Wow... I thought this might be one of those threads that was obscure enough to not get any replies... thanks for the info!

I'm debating giving this a try. The gauge is relatively inexpensive if I ruin it ($29), but I'm guessing my chance of success is slim.
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  #12  
Old 05-25-2009, 10:20 PM
FSJ Guy FSJ Guy is offline
 
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Where'd you find the inexpensive oil pressure gauge???
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  #13  
Old 06-01-2009, 09:39 AM
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The gauges are made by Cyberdyne and I purchase them from Jegs.com
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Old 06-01-2009, 12:56 PM
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I know it's pricey..but BJ's has their Dakota guages for that year..
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Old 06-01-2009, 01:45 PM
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I want to use the original panel, not replace it entirely.

Dakota Digital will also retrofit my panel with their gauges for $995... but I'm thinking it is doable with a little help from my friends.
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Old 06-01-2009, 04:18 PM
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I am going to have to go with Joe here. Excellent write up of instructions. I have had the pleasure of doing everything from through hole hand placement to fine pitch SMT repair by hand. It is all about using the right tools and taking your time.
I think you could make it work very well.

Good luck.
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