USM’s exclusive DashTuneline of dash upgrades for 84-89 Corvettes.  The color combos and options allow owners to fine tune the appearance of their interiors.  Dashes remain fully functional & the upgrade is completely reversible.

 I used my ’85 as one of the testers for these products. A few photos are available at usmracer.com.  My favorite combo so far is White/White/Red (not pictured). This means the Digital Graphics & Bar Graphs are White while the warnings (temp/pressure/over-rev) remain Red. With this combo the graphics seem clearer and cleaner, and more consistent with the ‘function over form’ theme of the C4’s.

The response from customers has been fantastic and everyone has their favorite combo. Blue/Red and Blue/Green are very popular. 

Some dash tech………. Digital Dash

 My dash had a problem.  The numbers for “Instant/Avg. MPG” were not complete.  Also, the dash would blink now and then, or go dark when I hit a bump. So, I guess my dash had two problems.

The design and build of these dashes are still, even now, very advanced and, although somewhat complicated, robust and pretty reliable. They are, however, prone to a number of issues. 

Below is a list of some common dash malfunction symptoms with possible causes and fixes. Some of these symptoms may apply to other dash systems and electrical gauges.

***Do not attempt these checks or repairs if you feel you do not have the skill or experience****

Illumination and Brightness

                Blinking/Black-out – Assuming the bulbs are OK, check power & ground. Make sure these connections are clean and tight. Make sure the wiring at the dash connection is not chaffed or broken. Make sure the connector terminals are tight (female). The large terminal carries the power/ground circuits and the smaller connector body is for the DIC interface.

                If all this checks out, the problem is most likely inside. I am not going to give a component tutorial, but I will point out two places to check that usually cause the problem.   The first is the bridge pins that connect the two boards electrically. It is common to find the solder on these pins to be bad. The second is the power supply. Outside the scope of this newsletter, I recommend sending this out, although you can check the ribbon connection soldering and do a visual for burnt components.

                Dim or Brightness – If you find the dash does not brighten in daylight or dim in darkness, the problem could be the light switch/rheostat, the light switch wiring or the photo sensor. With the dash on, pull the light switch to the park light position. The dash should brighten. Now, with the switch in the same position, turn the switch knob left or right and the dash brightness should vary. Not far from the light switch there is a small square ‘hole’ in the bezel for the photo sensor. This sensor is used by the dash circuitry to adjust display brightness based on ambient light. If you block the light the dash gets dimmer. If, say at night, you shine a flashlight at it, the dash should brighten.   

Display Quality

                Random display- A few dashes I have seen go crazy when ignition is on. Some segments light then go out. Same thing happens with the bar graphs. Everything is random. Most likely, this is a bad power supply or bad power side connection. If the power and ground wiring is good, and the car battery is fully charged, send it out.

                Segments – The dash seems to work OK, but some segments don’t light up. This is usually one of three things. The LCD panel driver is bad, which I have only seen once. The LCD panel is broken. Or the jumper (a rubber/conductor laminate) between the front board and the LCD panel has a bad connection. The last two are usually the result of a dash that has been opened and not properly reassembled. Some customer’s LCD panels had been improperly installed and were either cracked, which is visible with the dash assembled, or the panel may be chipped where the jumper interfaces with it. Along certain inside edges of the panels are electrical contacts where the jumper connects the board to the panel. If one of these edges is damaged, the electrical connection may be open. Also, if a dash is not carefully rebuilt, debris can get between the jumper and board or panel and block some or all of the segment control signals.

Display Accuracy

                The accuracy of the dash display depends on several things. The sending unit must provide a usable, calibrated signal. Having a correct, properly operating sending unit is important. The wiring carrying this signal must be intact and free of noise. Make sure this wiring and all signal wiring is kept away from ignition wiring. Finally, the signal is processed by the dash circuitry for display. A quick check you can make for the coolant sender, oil pressure sender, & oil temp sender is to check each circuit with the respective connector disconnected (open), and the lead grounded (shorted to ground). **DO NOT LEAVE THE CIRCUIT GROUNDED FOR TOO LONG*** NEVER GROUND THE TACH CIRCUIT*********

Coolant………….open will read LO………..shorted will MAX out

Oil Pressure….. open will MAX out………shorted will read ‘0’

Oil Temp………..open will read LO….…….shorted will MAX out

I hope this information is helpful.

Any questions about dash diagnosis or repair feel free to call.

Don’t forget about our new DashTune upgrade and your exclusive invite to save almost half off!! Once again this is for a limited time and only one per customer.