johnnyboyC4

I'm going to be attempting to rebuild my LCD screen on my 1984 Corvette in the next few days.
I've got the soldering iron and solder, the desoldering braid and clean solder. I was wondering if I needed any "special" solder to put on the parts, or if the generic stuff I have will work.
Also, I wondered if there was anything I had to do to the motherboard to prepare for the work that I'm going to do. Do I need to use clips on each wire while I heat the back of the board up?
I'm getting a lot of feedback from everybody I know, but none of them deals with this kind of stuff. I think they're talking out their *** mostly...I wanted some feedback from some people who have done this kind of work before.
Thank you,

HlhnEast

I didnt have to get into mine too deeply but I recommend a soldering iron of 100 or less watts to keep the hear soak from going too far.

What exactly is your problem? The LCDs are not soldered to anything.

johnnyboyC4

The screens themselves are fine. It's the information that isn't right. I turn my car on and all the readouts get maxed out and never come back down. All the screens light up but don't do anything. I was having problems with my engine ground wires that caused my dash to go dark. When I fixed that problem, it began to illuminate again, but none of the information was right. I saw on a previous thread how one guy explained how to repair the thing, and now that I've got all the stuff to do it, everybody I know is trying to give information on something they know nothing about.

GREGGPENN

Best link/write-up passed on to C4 owners is here...
http://www.batee.com/corvette/dcrg/r...tor/repair.htm


Note the recommendation for 60/40 solder and a pencil (low-heat) solder gun.

I don't know if all (84-89) units are the same but I just got thru doing this. I had intermittent, unlit sections of the dash -- though the LCDs continued to operate.

After separating the back from the unit, then separating the front & rear circuit boards, you have access to the light sockets. By bending the socket's tab's to create more pressure, I believe I solved the problem. I lightly sanded all contact points of the (1/4 turn) screw-in light sockets to insure contact. I also used fine steel wool on the circuit board mating points. Finally, I used a trimmed fingernail file to remove any oxidation from the light-bulb clips inside the socket.

You will find the attached link recommends other soldering and extra ground. Since my car is still fairly new (with only 60k miles and always parked indoors), I did no additional service other than redo the light sockets.

BTW...I also did the miniture sockets that house the blinkers and hi-bean indicator.

The only other "trick" is the retainer clips for the main plug-ins. I believe the safety clips were blue and green (one each). Use a screwdriver to pry those safety clips up/out. (Don't force.)

To re-install the acrobatically-located bottom screws, put tape in your 9/32n'd socket. One strip of masking tape was enough for me. That allowed the screw to be gripped firmly enough not to fall out while to feed it back into location.

Good Luck.

johnnyboyC4

There's two different guys selling refurbished LCD dashs on eBay right now. One says that only the '84 and '85 can go together and the other guy says that all dashs from '84 thru '89 will work in all the cars so I don't know who to believe. I went and bought a LCD dash from a junkyard couple of months ago from an '86. It lights up just like my '84, but none of the screens show any numbers. It just gives the green bars.
I mainly bought it because the odometer only showed a little over 86,xxx while my car has over 134,xxx. It's also badly sun faded and I was planning to rebuild it to test my skills before tackling my own dash.
Half the light didn't work on it when I plugged it in, so I went at got all new bulbs from NAPA. Now everything lights up, but nothing is acurate.
So I'm tending to believe that '86-'89 are on a different system.

87 vette 81 big girl

I would send your original 1984 LCD Instrument cluster out for repair if you can afford the $300 - $500 service & rebuild charge.

1984 LCD Displays are unique from the 1985- 1989 units.

If you have "0" electronics repair experience,
you will make your LCD instrument clusters inoperative or damage easily.

The power supply fails most often in the 1984- 1989 C4 Instrument clusters.

Sunburnt LCD displays & burnt out light bulbs are very common.

johnnyboyC4

I was mainly curious how to go about testing the Dash outside of the car. I see all the pictures on eBay of the ones that have been refurbished lying on towels or leaning against a wall all lit up and was wondering how to go about supplying power to it so I can see if it is the dash. It may just be a short in the dash harness that's causing the problem or it could be the ECM that went out.
The car cranks, idles and the information center works correctly and all the interior lights work too, just not the LCD screen.

87 vette 81 big girl

Some of the Veteran Corvette mechanics I have met or known since 1983 have told me that some AC Delco service centers had specially built Signal Generator devices just for the 1984 through 1989 C4 LCD digital instrument clusters.

And same test signal generator for C4's were also used for other GM vehicles with factory LCD or Vacuum Fluorescent display instrument clusters.

AC Delco electronics was originally headquartered base in Anderson, Indiana.
Who made all 1984-1989 C4 LCD display units.

The US recession from 2007 to present Killed AC Delco in Anderson, Indiana.

Doors shut down.

Just a few guys in the USA have those special AC Delco digital display test signal generators.

I have seen only 1 in person at Bill Jacobs Chevrolet in Joliet, IL.
It was at the swap meet just for Corvette guys on a fall weekend.
Around 2003 or 2004.

Seller wanted around $1,000 cash for it.

Had no c4 yet & not that much $$ with.
passed on it.
Was a very cool electronic GM instrument cluster testing device.

BR

johnnyboyC4

Is there any way to test the dash out of the car? I have one of the digital dash test kits, but I can't find the right attachment to plug into the dashboard

leesvet

having the displays go to MAX possible reading (default) is telling you that there is a disconnect between the display and the sensor supplying that variable resistence signal.

Oil press for example...a reading of 80 means its disconnected.
IF they are ALL doing this, the problem has to be a common connection...and the ONLY possible place is the main plug-in on the cluster.

Dive in. Go find a jewelers headset magnifying lense, and get a good bright lite and dive in. Just start with the pins in the socket and search continuity. Go from pin on the cluster and follow the path on the board.
Also test the harness the same way.
Its got to be obvious........the odds of all the display sensors failing or being d/c at the same time are astromonical, unless something cut wire somewhere.

HlhnEast

Lee is on the right path here. Go to batee.com, look up the wiring diagrams and they will tell you what each pin of the connector is supposed to have on it. Go thru each to at least eliminate the input to the dash before tearing into it.

johnnyboyC4

I found someone here that will diagnose the dash for me for only $35. Saves me time and money not rebuilding it if there was nothing wrong to begin with. He tells me there is a wiring harness attached to the top of the transmission that could also be linked to my problem with the dash not operating properly. I looked it up in my Chilton manual and it does say that I would have to unhook it in order to drop the transmission, but it does not say what function it serves. The guy over in Dallas tells me that it is a simple harness and I could have hit a rock or something and simply dislodged the connector. I need to get under there and see for myself what damage has been done, fix it, and see if the dash works again.
I am taking it over to him on Tuesday. I don't want to waste time and money rebuilding my dash if it's simply a wiring issue, or if the problem lies somewhere else entirely!
Does anyone know what function this harness serves and what each wire goes to and controls?
I never even thought to look at the transmission as a probable cause of my problem because I was not aware of any wiring harnesses connected to it in the first place.

87 vette 81 big girl

The Tachometer Filter.

Its a "PIE" style "Choke filter with capacitors bridged in the circuit too.

Supposed to eliminate a High KV voltage spikes & RFI and send them back to chassis ground.

Then the untainted HEI tachometer signal is sent to the LCD tachometer electronics/ display.

Be a good idea to check to see if the tach filter is connected or not on your 1984 C4.

BR

johnnyboyC4

I just re wired a brand new tach filter on my car about three months ago and it did not help with my "spiking" problem. Something else must have been causing another problem as well. The old one's wires had burnt out on both ends and someone else had wired around it. It was still on the rear of the engine, but no wires were going to it. I got a new one from Eckler's and installed it, but the dash still kept spiking on me.

87 vette 81 big girl

Like Greg,

I took apart my 87 LCD instrument cluster carefully to change out the tiny halogen back lighting bulbs.

And troubleshooted the Tachometer portion of the instrument cluster.

It turned out the LCD display was defective.
I replaced it with a another known good one.
Tachometer works perfect always now.

Prior the numerical portion of the Tach would read erratic numbers or letters instead.
And colored bar graph display would flicker & jump around random.
Especially when I floored the gas & let the TPI engine wind out till it ran out of air.

The old tachometer LCD display in my 87 must have taken a High KV spike at one time.
Because after removing the tri- colored plastic film & holding the Clear LCD up to a bright light,
I could see definite shorting bars present in the near invisible printed circuit wiring traces not present in the other know good LCD display.
Tilt that LCD display left or right & up & down,
You can see the printed circuit traces & were the special LCD chemical normally resides.

One of my old electronic teachers from college when I earned my AAS in Electronics Technoolgy Degree many moons ago taught me & others all about LCD & electronics.
He invented the LCD display in the early 1960's.
He claimed it proudly at least.
I heard it was a joint effort by the old BELL - Honeywood Howell laboratories.......
Sometimes I would question him who invented the LCD display back in 1987..........Him or Bell Lab..............
He would flip out on me & rest of 7 group of guys................."Me of course Dammit Brian".............LOL

Was a cheap laugh always.
He had a worse temper than myself.................



BR