C422

So, my 90's dash started to give me some problems intermittently. Specifically, sometimes segments would dim (not the back lights, the actual LCD) and segments that shouldn't be on would be partially on. This made the speedometer very hard to read. Speeds like 35 and 55 looked almost identical. Here's an example of what mine was doing:


and another:


A lot of people have problems with cracks in the solder over time, and sometimes the Batee's articles don't work, or your 'Vette is too new (a 90+) for some of the fixes for the older ones. Instead of sending that unit off for a $300 repair, or finding a salvaged one, give this a whirl:

Take all the bulbs off of the digital dash cluster.

Preheat your oven to 385 degrees Fahrenheit (140 C), and make sure it's actually at or over this temperature.

Wrap a cookie sheet in tin foil, and wad some tin foil up and stick in through some of the light socket holes to support the board. You don't want any ICs to touch the tin foil, and don't want the wires for the LCD connector to touch the foil either. Here's a picture so you can get the idea:

Put this setup in your oven for about 9 minutes. This will reflow the solder, which should make all your connections again. Do NOT put your LCD in the oven. Only the board, like in the picture.

Take your board out of the oven and let it air cool. Don't try to help it, you need the board to cool on its own. It's possible your board may warp slightly if you don't have it properly supported. This isn't bad, but it's definitely not better, so try to support it well. The extra quarter for the tin foil won't kill ya.

This is commonly used with electronics to repair broken solder connections at home. Laptop motherboards, graphics cards, Xbox 360s, etc, can all be fixed this way.

I am in no way responsible for you setting fire to your house, blowing up your speedometer, etc. Always make sure to visually inspect your board before putting it under any heat source. If capacitors are bulging, or something look torched already, don't bake it. If something DOES burn up, don't breathe it in. That crap's not good for you, and it stinks.

This is SIMILAR to how actual electronics manufacturers melt their solder. No, your oven's not as good as theirs, and they have a lot more safety features, but the concepts hold.

Have a good one.

HlhnEast

Neet! I am assuming all the stuff then on the board is resistant to the 385* if the manufacturer uses a similar method. The earlier boards have power supplies and plastic connectors and such. Just curious if these notoriously cold soldered boards could be helped by this.

C422

Very very likely. Part of the reason you let the thing cool down naturally is to let anything that's gotten melty get hard again. You might notice some fluid on the board, but that's not a problem (it looks kind of blackish brown). I forget what the stuff's called, but it's a natural byproduct, and not your board falling apart!

MotorCity_87_C4

If there are any Semiconductor chips or transistors on the circuit board you run the risk of destroying the parts due that extreme heat for the 9 minutes. Heat is the worst enemny for semiconductor chips, The manufacturing process uses the minimal amount of heat to do the soldering.

BTW in a previous life I was an Electrical Engineer with Semiconductor design experience and I've also worked in the assemply of electronice circuit boards.

C422

My Electrical Engineer father, who worked on design and fabrication of semiconductors disagrees with you.

As an Aerospace and Electrical Engineering student (senior year) working toward his PhD at the top school for Aerospace Engineering and top 5 for Electrical Engineering in the world, I disagree with you.

Heat is only bad for components if you're running current through them, or if they have never previously been heated. Yes, in a factory reflow profile, you have the preheat zone. This is accomplished in this case using the tin foil. It helps to reflect the heat from the plastic IC side of the board. The reason you have to have the oven preheated already is so that you don't have a problem with flux (the term I forgot earlier) evaporation. Typically, heat soak is over a minute, sometimes 2. Surface-mount Technology (SMTs) like the resistors on the back of the board are rated for 260 Celsius (500 Fahrenheit). Since liquidus state of older, partially lea-based solders is in the 360 to 375 range, 385 is actually arguably too LOW for a full reflow phase. The flux that is remaining in the joints from the factory still helps with lowering surface tension and then helping the solder "dry" in this state. This is usually a one minute process.

So, 9 minutes in the oven allows you to heat the board to 385 from room of 75 or so in about 4 minutes, using household (conventional, typically, though convection isn't any worse) oven heat, as opposed to an IR oven. With your household oven, you lose enough heat to take 10 minutes to fully reach your operating temperature, on average. This means that the 385F is basically the MAX the oven gets, and it's right at the end of the reflow zone, like it should be.

And then you let the board cool in room temperature air at its own rate so that the solder does not become brittle. Period.

385 for 8-10 minutes is the minimum amount of heat needed to reflow the solder. That's why professional repair shops do it that way, and that's why people repair Xbox 360s that way.

I don't appreciate the "I'm more qualified than you" argument, especially with something that's been used properly for a lifetime, and especially without knowing the background of the person you're trying to talk down to.

MotorCity_87_C4

I said you run the risk. Just saying......

kwd1

So did this fix your dash?

Phat98

All that education and you forgot the word "flux"? And flux is not a 'natural byproduct', it is introduced with the solder to prevent oxidation at the joint of the solder.

I don't have all the "high-falootin' schoolin'" you have, but...I have an Associates in Avionics Technology from CCAF, attended the NASA High Reliability Soldering Course I and II (passed!) and spent 20 years working a Pace soldering bench, soldering on everything from tube sockets to ribbon cables, SMTs, and multi-layer circuit boards. Unless you have a calibrated oven and the technology and equipment to thoroughly function check that board, it's a crapshoot.

As far as the "I'm more qualified than you" argument and "trying to talk down to"...lighten up and grow a thicker skin. The poster never went there, he just presented a possible caveat with some background to back up his statement...as I did. We appreciate your post and your documentation efforts, that's how we all learn...just don't get so defensive when someone questions it, you'll live longer.

Now, the question posed by kwd1 remains...did this fix your dash?

Benny42

A little while with a temp controlled grounded iron is way safer on these old parts.

C422

I'd gone through it by hand once, and had someone with lab tools go through. By hand, you can't keep consistent temperature and make sure that the solder reflows.

Fixed my dash fine. I should add a bit of silicon around the rubber/felt backing piece (it's come apart) because I can see it through the LCD at the moment, but the numbers are spot on. And have been for a while at this point.

As far as the thicker skin goes, maybe I overreacted. I didn't take it as a "I'm qualified" at all, and if it was harmless, I severely overreacted, and I apologize.

2fas2c

Interesting write up. Typically when the LCD has this issue it is the pins separating from the glass/epoxy. Anyone have any tricks for removing the old epoxy from the glass? The last time I repaired one of these I spent hours shaving it off with a razor blade, what about using a cheap soldering iron with one of those scraper type tips and melting/scraping it off??

TPI350

i need a 87 digital cluster.. mine lights up but no numbers unless i use polarized sun glasses besides on the tach it shows my idel wich is 9, my info lens is cracked to hell and my speedo is just blank even with polarized sun glasses... please help i have a long drive in a couple weeks from florida to ohio i need to fix this somehow without spendin 300-500 dollars

leesvet

You're going to spend $350 to exchange one. Thats the going rate. BUT yours must be rebuildable or it will cost you even more.