Instrument cluster problems?

1990 Chevy k1500... I have my instrument cluster out due to some annoying speedo problem and a bad bulb. Local Chevy dealer tells me they don't do repairs on site and send the parts out to AC Delco,
understandable. They recommended I go straight through AC Delco, and a local search finds me no local shops that repair instrument clusters, meaning I'd end up sending it out as well. I am hoping to open it up myself and replace the bulb and look for any obvious problems with the speedo gauge. I have a static-control wrist strap, but have one simple question... how do I ground my workplace? I'd be working on my Craftsmen workbench... the strap comes with an alligator clip that needs to clipped to a grounded surface. FYI the speedo problem: randomly, and mainly at low speeds, the speedo will drop off to 0. The engine does react to this, as it feels like the throttle was let off just a tad. If I leave it be after a few seconds the Check Engine light lights up, no blinking, just a constant light. A sharp smack on the dash will bring the speedo back and the Engine light goes away. Thanks for any info..
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Best to have a static mat that is grounded to earth ground through a 1 meg resistor. You could connect the mat ground wire to the screw on a grounded AC outlet. See this from RadioShack: http://www.radioshack.com/product/index.jsp?productId !02871&cp=&kw=anti-static&parentPage=search

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Grounding to the grounding conductor on your electrical system is a bad idea. If you would happen to have an electrical issue with some other part going to ground, what would happen? Also, isn't the point of a ESD ground to allow a path for any electrical charge to go to ground. Won't a resister resist this?

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wrote:

why do you think this?

then that oter part would ground out and still not affect what your working on. Pull the battery terminal positive off if your worried.

No a resistor wont hurt. A resistor resists current flow, not voltage and with a static discharge, your worried about voltage knocking out these parts, not the current. Ground in this case is what ever is as to lowest potential difference of voltage. The earth you drive on is not "ground" to the vehicle because its not part of the electrical circuit. Plus its insulated by the rubber in the tires. The battery terminal " --- " is connected to the chassis and so this is the lowest potential point in the electrical system. t is advisable to strap off to the pc board itself at a ground hole usually located around a screw head.
_eric
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Hi!

I'm not so sure I'd worry about it that much. You will do a very good job by dissipating any stored up charge by touching a grounded metal surface periodically during your work and not moving around any more than you have to during the work.
Since you mention that whacking the cluster "fixes" the problem, I'd suggest looking with a magnifying glass for bad solder joints. With all the vibration that an instrument cluster experiences in its lifetime, I wouldn't be surprised if you found some.
William
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If you cant find the problem, i bet you could get another from a junkyard fairly cheap.
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I have a 91 electronic cluster that the speedo would go blank and the odometer would either ramdomly show jibberish or show "error" . Personally, i think there is good reason to be concerened about static, but people go retarded over it. Just make sure your youching or connected to a ground spot on the speedo's PC board while working on it. Never goto graba pc board without touching the ground points 1st. 18 years of electronics repairs and i have yet to knock out 1 piece from static. the chip your looking for will be about the size of a postage stamp. it will have about 10 legs comming off each side of the chip. Its also surface mounted so it its a bitch to deal with. To add to the trouble, they put a clear urethane type coating over everything and it wont solder nice. Your going to need a soldering iron with a real fine tip and just apply heat to each one of the chips legs-one at a time- for about 5-8 seconds. you will see the solder then kinda push out at the top of the chips leg or down by the pad. what your doing is resoldering the joint by just adding heat. forget about trying to add solder because the urethane will crap up the solder joint. BE CAREFUL NOT TO GET SOLDER BRIDGES between the ajacent legs. use a needle to scrape away excess solder that gets into the wrong area. If your instrument cluster is like mine, its all vacuum florescent displays. if the other displays light up, then the power supply board is working (located on the blue PCB) if they are all out, then the power supply daughter board is dead. There is a small 16 or 18 pin IC chip with the name "microchip corp" and id bet my left nut that its where the odometer readings are kept. Im used to memory IC's like these. resolder this too and ensure the connections are tight. Its not a surface mount so its easier to deal with.
There is more ive learned and i can share that later. Good luck and maybe take the bare PCB with the displays to a local radio repair shop to have the tech resolder , cheaper than replacing.
--eric
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captain knobs wrote:

Thanks to those that replied. After removing the instrument cluster (which uses dials for the indicators), I removed the clear plastic cover which gave me direct access to the gauges. They snap into the board via prongs, and each gauge is its own module that can be removed. I removed the gauges, which gives me access to all the bulbs on the board, so I replaced the dead ones, very easy.
I took care to clean all the snap connections of dust, made sure all the connections were tight, and snapped them all back in. It helped but didn't fix the problem, the speedo still craps out, but I no longer have to bash the top of the dash to get it back, now its a hardy tap. The Check Engine light no longer comes on when the speedo goes out, but strangely enough my odometer and tripmeter stop when the speedo does, which wasn't a symptom prior. I tried to take a look at the wiring harness but it's setup where it's held into the back of the dash, so when you insert the cluster, the harness is fixed and it snaps right into the cluster. Removing the harness to inspect it would mean mauling the plastic that holds it steady, and I'd probably never get that cluster lined up and connected again.
Next strategy is to find a junkyard cluster, and see if a new speedo gauge works, if that doesn't work then I'm removing the back plate and inspecting the circuit side of the board for anything obvious.
So now I'm wondering if a newer instrument cluster (up to 1995 trucks) would be compatible. If I get the chance to try it I will post results.
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