This problem seems to result from moisture on the circuit board that controls the LCD, and has reportedly been solved by cleaning and sealing the circuit board.
I have compiled suggestions from other contributors along with photos of my own project. Here are some tips that make a somewhat daunting project very doable.
Surprise, you don't have to remove the seat for this project!
A quick overview:
Disconnect battery and remove mirrors, windshield, windshield adjust levers, fairing pockets, ignition switch cover, top inner covers, headlight adjustment knob, foot warmer control knob ( SE models ). Removing the top compartment and radio/cassette deck� is called for in my manual, but I did not find removal necessary. Remove instrument panel cover. This is as far as my manual goes. Next: Disconnect instrument panel housing by removing four screws, separating speedometer cable and two wiring connectors. Remove six screws to remove clear cover from instrument panel housing. Remove four screws each on tach and speedo to disconnect speedo and tach from instrument panel housing. One screw to remove wiring cover from rear of instrument panel housing. Four screws to separate LCD assembly from instrument panel housing. Four screws to access underside of larger circuit board. Clean with isopropyl alcohol, seal with acrylic spray lacquer. Consider replacing instrument panel lights while you have easy access to them. If changing bulbs, don't forget about the one mounted in the LCD assembly. Reassemble.
Some helpful details:
There are three screws holding on the mirrors ( blue arrows ), and one screw ( red arrow ) associated with the windshield adjust lever mechanism that also must be removed to get the instrument panel cover off. The fresh air vents located just below the speakers must be removed before the cover will come off.
Removing these without breaking them is probably the most difficult part of this job. Since you can't see what you are working with until you have it disassembled, I have included two views of these fresh air vents from behind the instrument panel cover after removal.
The vents have two tabs ( red arrows above ) on the top and two more on the bottom that expand behind the dash sub structure and the instrument panel cover. You must compress the tabs so the vent can pass out through the opening in both the dash sub structure and the instrument panel cover. In practice I found that the vent and tabs simply need to clear the dash sub structure. I removed the instrument panel cover with one of the vents remaining in it.
The Clymer Honda GL1500, 1993-2000 manual describes removal of the fresh air vents as follows:
a) To remove the left-hand air vent, reach underneath the fairing and pry the two air vent locking tabs out of the instrument panel. Then pull the fresh air vent out of the instrument panel and remove it.
b) When working on the right-hand air vent, you cannot reach its' locking tabs from underneath the fairing. Instead, use a seal pick or similar tool through the small slits in the air vent housing and pry the locking tables out of the instrument panel. This procedure is difficult and remember, the locking tabs are small and fragile. When the tabs are free, pull the air vent out and remove it.
I didn't try this, but I wonder if a loop of thin wire passed behind a tab in the fresh air vent from the front/inside of the vent could be used to compress/pull the tab from the front.
There are four screws securing the instrument panel housing.
Recommend disconnecting speedo cable from front wheel as this will provide more slack for accessing rear of instrument panel housing, to disconnect the speedometer cable's
two electrical connectors.
Remove six screws securing clear cover to front of instrument panel housing. Keep track of the clock set switch knob when you remove the clear cover. It will fall off. The photo below was taken after all components were removed from the instrument panel housing, but shows the location of the screws that must be removed to extract the speedo, tach and LCD assembly. Remove four screws ( red arrows ) from behind the tach. Remove two screws ( blue arrows ) from behind the speedo. Remove one screw holding wiring cover in place ( yellow arrow ). Disconnect three electrical connectors between LCD circuit board wiring and instrument panel housing. Pull LCD assembly and attached wiring out through face of instrument panel housing.
Removing two additional screws ( red arrows below ) will completely disconnect the speedo from the wiring that attaches it to the instrument panel housing.
Empty instrument panel housing.
The LCD unit has two circuit boards on it. Reportedly it's the larger #2 ( as designated in photo below ) board that needs cleaning and sealing. I have [received] no guidance on dealing with the #1 board and chose to leave it alone.
Remove six screws to separate #2 board from mounting.
The circuit board will remain attached via three ribbon cables, but can be laid out and masked for cleaning and sealing the underside � ( shows just a bunch of solder connections on it ). I removed the tape on the circuit board, shown in the photo below, for cleaning and sealing then replaced it for reassembly. It seems to be located to provide a barrier between the sharp solder points and the wiring compressed against them when the LCD unit is assembled.
alcohol and an acid brush to clean the #2 board thoroughly. When I began cleaning I found a brown tinged sticky layer on the board surface that seemed easily dissolved by the alcohol. I continued to apply alcohol, scrubbing � the board with the brush and wiping off the brush between applications, until the surface appeared clean under a harsh light and the brush was no longer leaving any brownish material on my wipe towel. This process required four cleaning and drying cycles.
The recommendation I've received is to use 99% isopropyl alcohol. I could not find 99% isopropyl anyplace, so chose to use 91% isopropyl which I found at Walgreens. Don't use the 70% isopropyl as there is too much water in it. Acid brushes (black nylon bristles, rolled metal handles also used for applying soldering flux ) are available at Home Depot and ACE Hardware.
If there is any corrosion evident (usually looks white/powdery) remove it using hand sanitizer and a worn toothbrush, then follow up with isopropyl alcohol. Allow the board to dry completely.
Recommend using a clear acrylic spray lacquer as a conformal coat to seal the board. Use several light coats; heavy coat will take a long time to dry. Suggest masking/covering the board connectors and the rest of the LCD unit carefully to protect them from over-spray.
With that whole repair process in mind, maybe it's 'freeing'� in many
ways to just let the clock be wrong!
Good luck and report on your results or additional suggestions!
Happy New Year.