[OKDXA] Simple Tech Trick #77

[AC5UP]

About 25 years ago I bought a Fluke 77 digital multimeter. Accurate and 
well made, it has stood up well against the normal wear & tear of life 
on a work bench. I don't play rough with my toys, but I do play with them.

For the past few months the display panel has started looking a bit 
puny. Like an LCD calculator with a weak battery the contrast was poor 
and the viewing angle was critical lest 8's look like 3's and 5's 
resemble 6's. Don't even ask about 4's and 9's. Finally tore into it 
last night...

LCD display panels use a gel-ish liquid trapped between two glass plates 
with the bottom plate electro plated in a thin series of traces to 
connect the segments to the header. Because of the heat sensitivity of 
the assembly they aren't soldered and typically connect to the outside 
word through a ribbon cable arrangement or a carbon fiber setup mounted 
in a way that keeps the fiber tips in contact with the matching PC board 
pads. Fluke used the carbon fiber feedthrough technique on this one.

Disassembled the meter, removed the LCD module, cleaned up the PC board 
pads with a Q-Tip moistened with WD-40, buffed the residue off with a 
piece of paper towel followed by a dusting with a small paint brush. 
Then I blew any residual dust from the area. Let's just say the pads 
were pristine within a minute or two. As for the carbon fiber tips, 
gentle dusting with the paint brush. No need to risk breaking off the 
fiber tips or encouraging the conductive material to recede into the 
insulation.

Reassembled, flipped the switch, and was rewarded by a crisp display 
that reads easily from any angle. Good as new and that put to rest any 
thoughts that maybe an LCD goes bad with age... Nope, it wasn't able to 
draw the current it needed to fully polarize through oxidized contacts.

BTW: Was going through some Tektronix service literature and was 
surprised to see they approve of WD-40 used as a volume control cleaner. 
Also OK for rotary and not-sealed switches. Been doing that for years. 
Just avoid hosing down the associated circuitry (especially padder caps) 
and try using a paper towel as overspray protection. Give it a quick 
squirt then exercise the part. Consider a second squirt if needed.

Also learned something about LED flashlights this week. Unlike 
incandescents that grow dimmer as the batteries age, an LED will hold 
full brightness right up to the point where the batteries are just about 
gone then dim quickly. Mixed blessing on that as you can nurse a weak 
flashlight in a pinch but with an LED you know the batteries are shot 
within a matter of minutes. At least the battery life is much longer 
with the LED. Just be sure you have a spare battery if you carry one in 
the car or consider replacing the batteries as an SOP thing in the fall 
since winter is when you'll most likely need it. Longer nights and all 
that... ;)