This is probably the single most common problem with older Fluke DMMs such as the 83, 85, 87, and 88 models. Referred to as “faded digits”, “faded segments” or “fading display”, it happens when the connections between the printed circuit board and the glass display panel become contaminated enough that the liquid crystal display (LCD) does not receive enough charge to flip all it’s little crystals around and become nice and opaque.
elastomeric connector is used. It’s basically some conductive strips embedded in a flexible rubber-like material. The appearance leads to them being called “zebra strips.” A plastic support structure combined with either screws or clips are used to keep the connector under slight pressure, to maintain good contact and seal out contaminants.
(Too Much) Resistance Is Futile
Metal-to-metal low resistance connectivity is not necessary because of the low currents, but if oils from the elastomer leech out, or other contamination invades the contact surface, it will reduce the signal enough so that some segments get dim. The 80-series display is multiplexed, so one single bad connection can dim a whole group of segments. The pink elastomers that Fluke used in the early 80-series meters are known to have this problem, enough so that Fluke changed to a different gray-colored connector somewhere during the life of this product line. Replacing the old pink connectors with the newer gray type is the only solution recommended by some.
However, I have found that simply cleaning the old ones will suffice most of the time. It is true that at some point in the future the cleaning procedure will need to be repeated. But if you do a good job, it is very likely to work for a number of years. [Update: One year after this procedure, this unit started to exhibit segment fade once again. So be prepared to repeat the cleaning process periodically.]
Fifty Shades of Gray
Important: If all of the segments are uniformly dim, then it may not be a problem with the connector strips. Often the cause of that is a ruined top polarizer, which can happen if the meter is left in direct sunlight for really long periods of time. The segments may look brown instead of black or gray. Time for a new LCD in this case. Or wait for another extreme repair article…
Let’s take this one apart and fix it. Remove the 3 screws in the back and take the case halves apart. Disconnect the battery and lift the meter assembly out of the case. Note that there is a top shield and a bottom shield held in place by a single screw in the back. Remove the screw and lift the rear shield starting at the bottom; finish by unhooking the “T”-shaped tabs at the top, taking care not to break them.
The top shield is held on by four barbed clips under the corners of the display bezel. These clips are somewhat fragile, if you break one it will ruin your day. Start on the right side (looking at the assembly from the back) and release the two clips with as little pressure as possible. If your model has a backlight, there will be a 2-pin connector that must be de-mated. The board can then be slid out from under the clips on the other side.
Detach the bezel by prying gently under the top edge (best to use a plastic tool.) The LCD should lift right out. Since the elastomeric connectors have been compressed against the glass for all this time, they should be securely stuck to the LCD, and will come out as well. It is best to put the connectors back in the same position and orientation they were in, so label them for that purpose.
After All These Years, I Just Can’t Let You Go
Very slowly and carefully pull the connectors from the glass. It should help to rock them from side to side to break the seal. The key is to not tear the connectors, which is another way to ruin your day. It will not be unusual to see some black residue left on the glass where the conductive strips were. [Update: Several readers report success by cleaning only the PCB side of the connectors. The connectors are not glued on, but if you’re squeamish about pulling them off, you can try just cleaning the PCB side. I’m documenting the full procedure here for completeness.]
The supplies for the cleaning process consist of the purest isopropyl alcohol (IPA) you can find (91% or better) and a heap of Q-tips (cotton buds). Dampen one end of the Q-tip and roll along the edge of the LCD to clean it. Use the other dry end to remove excess IPA and the contaminants that get floated. When the Q-tip gets dirty, toss it and get a clean one. Continue until the contact surface is clean. Replace the LCD (don’t forget to check the orientation) in the display frame and clip the bezel back on.
Now perform the same type of cleaning process on the edges of the connectors, using the wet end / dry end method. It is best to use tweezers to handle the connectors, because skin oils can contaminate the contact surface. Slip the connectors back into their original position and orientation. Use the tweezers to seat the connectors in fully. Set the display assembly aside.
Contacting the “Other Side”
Again with the wet end / dry end method, clean the PCB contact pads. If the pads are metal and in really bad shape, a fiberglass scratch brush before the IPA/Q-tip cleaning can help. Some models have black polymer thick-film (PTF) contacts. Do not use anything more abrasive than the Q-tip on these.
Almost done. Slide the PCB under the clips on the left side. Align the 2-pin backlight connector and gently press the assembly back together. It should not take much force at all, if it resists, then something is not aligned. Check everything and try again. When everything is seated properly, reattach the battery and turn the unit on while holding any of the buttons down. (A 3/16″ Allen wrench is handy here for turning the switch.) All segments should be nice and black now. If your meter is dirty, it doesn’t hurt to take the plastic parts and the keypad, and give them a good scrubbing before completing the reassembly.