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
Thanks for any info..
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:
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
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
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.
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.
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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