225 Yamaha with LCD gauge for voltages, time, trip odometer and fuel
quantity. The bottom, of about eight, fuel quantity LCD segment blinks
continuously even though there is 1/4 to 1/2 tank full of gas. The wiring I
accessed was OK for continuity and ground. I'm thinking it's time to try a
sending unit. Before I spend the $80 or so for it are there any other things
I might try looking at? TIA

Shack wrote:

225 Yamaha with LCD gauge for voltages, time, trip odometer and fuel
quantity. The bottom, of about eight, fuel quantity LCD segment blinks
continuously even though there is 1/4 to 1/2 tank full of gas. The wiring I
accessed was OK for continuity and ground. I'm thinking it's time to try a
sending unit. Before I spend the $80 or so for it are there any other things
I might try looking at? TIA

Since that is more or less "disposable" at this point, try this.

Those LCD displays typically make contact with a number of contact spots
on a PCB. The contact points on the LCD display (the piece of glass
with sandwiched segments) are held in contact with the spots on the PCB
and that is how the segments are activated. If that gets a little dirty
or oxidized, the segments won't work.

If you can (carefully) disassemble the gage and identify the points of
contact, it may be that a little cleaning will get them working again.
Use a Q-Tip and Isopropyl alcohol to clean the contact spots on the PCB
and also slide an alcohol wetted Q-Tip along the edge of the LCD that
touches the contacts. That edge of the LCD may look like (in an edge
view) like two thin sheets of something dark with a thin sheet or
pinkish rubber or silicone separating them.

If the glass panel is stuck down into a socket type mount, try sliding
it out and cleaning down in the socket (toothpick and paper towel) and
on any contact edge or obvious contact points.

For more obvious surface corrosion, one of those old typewriter ink
erasers that are slightly abrasive (use it gently!) may be helpful for
cleaning.

Put it all back together and it may work.

I have to clean the contact points on the LCD display on my venerable
old Fluke 79 multi-meter every three of four years when the upper half
of the segments start dimming. This is pretty simple to do and, after
cleaning, the display is as dark, distinct, and crisp as it was when
new. It is like welcoming an old friend back from a near death
experience. :) And I usually put in a new 9V battery while I have it
open but the battery alone will not resolve the dimming display issues.

Good luck,

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)

Jack,
Thanks for the diagnostics. I'm leery of opening that particular can of
worms just yet as I could, and probably would, induce even more problems.
The fact that the bottom segment is blinking leads me to think the assembly
may believe I'm real low on fuel. I did look at the gauge and all the
exposed metal, e.g contacts, are shiny, no sign of oxidation. I'd like to
know what kind of data the sender unit sends to an LCD type of display. Is
it just resistance or capacitance or what. In other words could I simulate
it at the sender unit wiring by causing a short or open or some specific
value of impedance. If I could do that without risking damaging the gauge
that might point to the culprit. But, between being brainwashed about ESD
damage and fear of destroying wafers and PCBs I'm taking a slow approach.
Again, thanks for the suggestion. I may try it yet.
Shack

"Jack Erbes" wrote in message
...
Shack wrote:

225 Yamaha with LCD gauge for voltages, time, trip odometer and fuel
quantity. The bottom, of about eight, fuel quantity LCD segment blinks
continuously even though there is 1/4 to 1/2 tank full of gas. The wiring
I
accessed was OK for continuity and ground. I'm thinking it's time to try
a
sending unit. Before I spend the $80 or so for it are there any other
things
I might try looking at? TIA

Since that is more or less "disposable" at this point, try this.

Those LCD displays typically make contact with a number of contact spots
on a PCB. The contact points on the LCD display (the piece of glass with
sandwiched segments) are held in contact with the spots on the PCB and
that is how the segments are activated. If that gets a little dirty or
oxidized, the segments won't work.

If you can (carefully) disassemble the gage and identify the points of
contact, it may be that a little cleaning will get them working again. Use
a Q-Tip and Isopropyl alcohol to clean the contact spots on the PCB and
also slide an alcohol wetted Q-Tip along the edge of the LCD that touches
the contacts. That edge of the LCD may look like (in an edge view) like
two thin sheets of something dark with a thin sheet or pinkish rubber or
silicone separating them.

If the glass panel is stuck down into a socket type mount, try sliding it
out and cleaning down in the socket (toothpick and paper towel) and on any
contact edge or obvious contact points.

For more obvious surface corrosion, one of those old typewriter ink
erasers that are slightly abrasive (use it gently!) may be helpful for
cleaning.

Put it all back together and it may work.

I have to clean the contact points on the LCD display on my venerable old
Fluke 79 multi-meter every three of four years when the upper half of the
segments start dimming. This is pretty simple to do and, after cleaning,
the display is as dark, distinct, and crisp as it was when new. It is
like welcoming an old friend back from a near death experience. :) And
I usually put in a new 9V battery while I have it open but the battery
alone will not resolve the dimming display issues.

Good luck,

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)

"Shack" wrote in
ink.net:

Is
it just resistance

Yes....nothing special....same way-off reading the mechanical guages gave
you. The display is hosed, or you may have some supply voltage problems
feeding the display electronics from the battery. Digital displays, just
like the cars, has a voltage regulator dropping the battery to 5V or so to
keep the starting/charging/switching changes off the computer circuits that
won't tolerate it. You may have a bad display regulator IC in the
panel....common in cars. Wrong power supply voltage makes them snakey.

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.