Defeating the Dash

[militant_x]

So i woke up today and decided it was time i get to fixing that dash. I got the car almost 2 months ago now and i havent fixed it. Ive read up on it, in these forums and other sites and so i think maybe i can fix it.

My dash didnt display the sings of a bad ground, my turn signal lights werent always on. With the exception of those bulbs, the other dash ones never turn on. Speedo and tach are blank, and the only thing that i read a number off is the temperature and mpg.

So i take it apart, I have some snags along the way but eventually i get it out. I take off the back cover i see someone had already tried to fix the dash before.. Theres a wire connecting the ground pin on the interboard connector (bottom board) to where it should go on top... the little plastic piece that pins slide into is half melted/destroyed for the ground pin.

I felt so happy then, i thought that would be the problem.

Just to be safe i take the whole thing apart, clean everything and do alot of sodering to any joint that looked funny or held something large (capacitor etc).

I ran a new wire from ground at the interboard connector to the lights (just as shown in the DIY corvette information project).

I also ran a new wire like the origional repair person had done, but i found it hard to make it stay in contact with the top board. The connector looked really dead.

I put 4 new bulbs in, 194s not 882s, they are a loose fit and too large for the little metal caps to go back on... but i just want to see if it works.

I put it all together, run to my car (its now night time) plug in the 2 connectors and turn the keyforward.

The dash was dark. Pitch black, just as it was before. I check to see if atleast the temp guage still works and it does. (under a light of course).

What a let down.

I then decide to see if that wire i ran from the bottom board to the top board is actually doing anything. I pull off the back cover and disconnect the wire from the top board.. tape it so it cant touch anything and put the unit back in the car for a test.

Nothing has changed.

Im getting desperate, ive been dropped so low now. I take off the top board and start sodering every joint that looks faint.

I try to take the power supply boad off, but i chicken out after i have 2 of its legs out and 1 left. The last leg was impossible to get out, and any more movement and id be stretching the little ribbon cable.

I test again... no difference.

Reality sinks in, i know nothing about electronics i should be happy i still have my temp gauge.

i want to run a new ground wire to the door post thing. Only i have no idea how to do this or where to put the cable (both ends). The fact that the lights never come on is strange.... i mean.. if the turn signal lights come on shouldnt the other ones also? Im thinking its either a bad overall ground (but i can read the temp gauge).

Im thinking maybe its the power supply board (cause i didnt get to soder it).

Im thinking maybe it has something to do with the weird interboard connector ground (but i can see the temp guage.. thats the lower board!)

Im thinking its maybe the light bulb sockets, they looked really brown and nasty (but shouldnt i see everything else like i see the temp gauge?).

Im thinking, im hoping that the LCDs themselves are not dead. I dont know what that means or if its possible. It sounds expensive.

For whats it worth here are things i notice when i start the car.
The top corner of the speedometer suddenly gets a bit greener when the i turn the key forward, a few seconds later it goes back to looking really dead. This isnt very noticeable unless your just staring at it looking for a difference. Everything gets just a little brighter as soon as the key is forward, a few seconds later it looks dead.

On the plus side i learned how to solder today.
But its a really downer man... putting back together i kept picturing how it was going to look... Finally a fuel gauge! A tach!

but not for me today.

Help im really lost. Vigman save me.

 

[geekinavette]

Are the gauges working but just really really dim, so much that you can hardly see them?

If you shine a light on the photocell in the upper left corner (or cover it up if the ambient light level is high) does the intensity change?

Dead photocells are common and will cause a VERY dim display.

Bill

 

[militant_x]

My friend swears she can see the tach moving... ive looked hard and cant see it working.

I havent done the whole photocell thing. Though ive tried turning the headlights on and turning the dimmer to where everything else is really bright (like the radio/ac etc)... as far as my eyes can tell there is no difference.

Ill shine a light on it in the morning. Thanks man, i hope we can figure this out, school starts in a week its a long drive.

-chris

 

[geekinavette]

Well doesn't sound like a photocell problem then (though anything's possible).

I don't know how similar the 86 cluster is to the 84, but I know that 84 has two separate grounds, one signal ground and one illumination ground. As I remember one is on the passenger's side door hinge panel and the other is on one of the trans bell-housing bolts on the driver's side, but I don't remember off hand which is which.

Have you checked the LCD fuse? (again I'm assuming that the 86 is similar to the 84).

Bill

 

[militant_x]

Ive checked the fuses, they are good. Now i didnt know about the 2 seperate grounds, least in my head it opens up more options.

I still want to mess with the photo cell.

I doubt ill get more done tonight. I stayed up till seven in the morning pricing a set of golf clubs, some guy wanted to buy them.

From what i understand its possible for the lcds to be bad. A "bad lcd" is what takes the repair cost up from 200ish to 500ish. They just never say what a bad lcd is or how to tell if you have one.I HOPE thats not it, i mean, ive never seen a vette in a junkyard where would i get replacements!



I appreciate your time man. Thanks again.

-Chris

 

[Top]

You have two grounds in the 32 pin connector. D1 & D3. D1 is solid black and goes to the driver door post. D3 is black with a white stripe, it goes to the amibent override sensor on the bulkhead before going outside to the bell housing.

A simple test. Take some wire and push it in D1 & D3 connectors making a 'second' ground wire. Run the other end to the door pillar ground. See if your dash lights up.

Good luck.

 

[militant_x]

this door pillar ground? is that the thing above the light swtich, or that bare bolt on the door? Im sorry im slow.

-chris

 

[geekinavette]

Hopefully these pictures will work. These are from the '84 shop manual. G101 is the cluster power/illumination ground. (G106 is a radio/speaker ground). G110 is the cluster signal ground.

Bill

 

[bossvette]

there is a Corvette only junkyard not far from me

http://www.michigancorvette.com/

I have had good luck with them. They will ship parts, it is just easier for me to drive there.

 

[militant_x]

I stuffed 2 wires into the D1 and D3 slots... after i connected the connector to the dash, it was hard to verify that the wires were still stufffed nicely in there. I grounded those wires to various places... including running them all the way over to the engine block. I see no difference.

Ive also tried eliminating the photocell.. i read that somewhere. I put a piece of tape with a wire on it over the back of it, shorting it you could say. I can always take the tape off. I also ran a wire from the ground pin on the interboard connector to out side the dash so i could ground that by itself. No difference.

It could be that my connections are just really bad, but if they are not then the grounds are good.

The lights still dont come on.

btw, thanks the pictures do clear up some confussion.

Bossvette, if it turns out i need a new part, we will talk =). thanks.

-chris

 

[bossvette]

militant_x
they have an 800 number on their web page the Owner Barry is quite helpful and has helped me on various occasions.

1-800-533-4650 give him a call

 

[geekinavette]

Well sounds like you've got the grounds covered. Just as a sanity check I might go ahead and check for continuity directly at the bulb connection to ground.

This is a diagram of the cluster wiring:

http://misterbill.homeip.net/vette/instrument cluster inputs_outputs.jpg

Make sure you have voltage at pins C16 and D16 with the ignition on.

Bill

 

[militant_x]

thanks man. Looks like its gonna rain any min, so i gotta do these tests in a while.

-chris

 

[militant_x]

ok. I got out my dads old analouge multi-meter.. i dont know if its accurate but its good enough to tell me if they are getting power. Both c16 and d16 have power, i checked them each with the 2 grounds (d1, d3) and the bolt above the headlight switch. Im not getting power (no suprise) to the bulbs though. Im starting to think again maybe its the bulb sockets... all 4 dead. I dont think the bulbs are grounded badly because the turn signal lights work.


thanks bill.

-chris

 

[geekinavette]

Well crapola. I guess about the only other thing you can do yourself is check continuity across all pins of the board-to-board connector. That thing is notorious for not making good connections.

I can't think of much else that would be simple.

 

[militant_x]

So im going over the whole thing with a multimeter. A few questions:

1. how do you check if a capcitor works with a multimeter
multimeter has voltage(ac/dc) and resistance and DCMA (thats current in this case right? dc milli amperes im guessing).

2. should i have continuity from d3 to the ground pin on the interconnector?. I continuity from d1 to it. I also i continuity from the pin to all the lights.

The sockets appear to work also... well ive only checked one so far..

All the solder on the top board is realllly yellow and for the most part dull. Ive found that sometimes i dont have continuity unless i play with a part with the probe for a while and find its "sweet" spot. The ones ive resoldered make the needle jump to life with little effort... is it supposed to be like this or should i resolder EVERY single connection on the top board? Soldering the ICs looks a little scarry.

A reminder,I know nothing about electronics.


-chris

 

[militant_x]

Ok i hope this is it!!!!.

I checked all the pins in the interconnector for continuity between the boards. Two of them werent working.. the ground which i knew about and had rigged up a solution (took it off for the test), and then one i didnt know about.... the first pin (if you say that the ground pin is the last pin). Im gonna make sure it works then put it back together.. I hope this is the last time i have to take off both boards.


wish me luck... gonna do some more testing, then fix the above and see if it works.

-chris

 

[militant_x]

well, the lights light up now!.... but the whole dash is blank with except the temp guage. humm... i forgot to un-short the photocell.... could it be so bright that i cant see anything else?? im out on a limb here..


-chris

 

[geekinavette]

1. how do you check if a capcitor works with a multimeter
multimeter has voltage(ac/dc) and resistance and DCMA (thats current in this case right? dc milli amperes im guessing).

If the capacitor is in-circuit then about all you can do is make sure it's not shorted. A capacitor by itself acts as a short-circuit the instant you apply a voltage across it (which is what an ohm-meter does) and it quickly becomes an open-circuit as it charges up. You might see this effect with an analog meter (and sometimes with a digital one) by the needle (or readout) jumping towards zero ohms briefly the instant you connect the leads, then quickly climbs to infinity (open circuit).

And yes DCMA is DC Milli Amperes (current).

2. should i have continuity from d3 to the ground pin on the interconnector?. I continuity from d1 to it. I also i continuity from the pin to all the lights.

Well that may depend on whether the harness connector is plugged in. I don't know if the two grounds are connected internal to the cluster, but if the harness connector is plugged in then most definately yes (since they both connect to chassis common ground).

All the solder on the top board is realllly yellow and for the most part dull. Ive found that sometimes i dont have continuity unless i play with a part with the probe for a while and find its "sweet" spot. The ones ive resoldered make the needle jump to life with little effort... is it supposed to be like this or should i resolder EVERY single connection on the top board? Soldering the ICs looks a little scarry.

What you're dealing with is an insulating coating that they put on the PC boards. When you "play" with the probe you're poking through the coating to the solder. When you reflow a pin with your iron you're burning off the coating and thus your probe can come into contact with the solder without having to poke through the coating.

It's normal.

That shorted photocell will only cause your display to operate at maximum brightness...just like if you had a fault condition, like low oil pressure or overheating. I ran mine like that for several months, the only annoying part is that you can't dim it with the headlight dimmer knob at night. It should be fine to leave it shorted until you get the real problem figured out. As for what the "real" problem is...hmmmm, It kinda sounds like the liquid crystal itself is not being energized. I was going ask if you made sure that the switches on the control center were turned off (again I'm assuming that the 86 setup is similar to the 84?) but if you're not getting a tach or speedo display then that's not the problem. Maybe you're having a problem with those horrible elastomer(?) connectors between the LCDs and the PC board?

 

[militant_x]

well, i put the dash back in for now. Least the lights work. Ill pull it out again soon and try to hunt down this problem. I just wanted to get it in today because school is starting monday, and I have to go buy my books. Today my friend was dropping his engine in, i wanted to atleast stop by.

Last thing i did was take it apart again and unshort the photocell. Ironically the backlight just makes it harder to see the temp gauge and impossible to see the mpg gauge. Though that is somewhat of a lie because before they were impossible to see at night. What im saying is there is little contrast.

As for the pink blocks.. they were really stuck on the lcds i didnt take them off because i was afraid they might tear or something.

I called a vette shop today...

me: "so can you guys fix the dash"

them: "yeah, its one of two things... the grounds or the unit is messed up. It'l take me about four to five hours to check the grounds. If thats not it we send it to california which is a minimum of 500"

i was laughing... a repair shop "we send it out" lol. What thiefs... 5 hours to check four a faulty ground??? at like 70 an hour? HA!

lol, I owe you money Bill.


thanks for the help. We got the lights up!

-chris