A number of years ago I bought a Fluke 87 multimeter for a special purpose. With the job completed it sat around for a number of years. Now, I would like to use it again, but the display has problems. Some of the number segments don't function, some are sort of random.
Is there anything I can do to cure this?
Yup - Probably - Just this minute was working on a couple. Mine were purchased new in 1989, worked until 2 or 3 years ago.
It is not a difficult repair if you are generally acquainted with electronic equipment.
The LCD display is connected to the circuitry by some elastomeric (rubbery) ribbons with conductive strips in them. Apparently the connections deteriorate after some time.
I pulled my 87s apart, removed the PCB assembly, removed the phillips headed screw from the back of the PCB assembly and carefully removed the back and front shields. The display comes off with the front shield. Go easy, there is a litle connector on the left for the backlight.
Once apart, the contacts on the PCB will be apparent, clean them up as delicately as possible. I just rubbed them very lightly with a cloth with a little isopropyl alcohol. If you want, you can put it back together and try it at this point. If there is no change, proceed on!
Looking at the display, you will see that there is a front bezel that snaps off. Once the bezel is removed, the LCD is visible and may be lifted out of the frame. In all likelihood the two elastomeric strips will be stuck to it, they look like pieces of eraser with a gray layer in the middle. Pull them off the display to expose the contacts, which are just conductive films, barely visible, on the edges of the LCD. CAREFULLY clean the contacts on the edges edges of the LCD (I again used Isopropyl Alcohol) being careful not to let the solvent travel off of the contacts into the display proper. Dry thoroughly with a Q-Tip or lint-free rag. Then, clean the edges of the elastomeric strips, again carefully. Dry, and re-assemble, being sure to properly connect the backlight. The whole assembly snaps into place on the PCB, if it doesn't snap fully into place you will see only a partial display, just like the problem you are trying to cure.
That should do it. I just this evening worked on a few of them, all successfully. I was going to send them back to Fluke, but, being an obsolete product the quoted price was very high. They offered me a trade in against a new 189, but I figured I would try to fix the 87s because I had absolutely nothing to lose. So far, so good.
A few years back Fluke started offering a lifetime guarantee on the 87s. Call Fluke and check the serial number with them. They will be able to verify if it qualifies. Instead of your problem it could be theirs.
Louis --
********************************************* Remove the two fish in address to respondI have several old Flukes around here since they were the meters IBM used and I ended up with a lot of "broken" ones. Most of them have a little bezel of "IBM card" stock between the LED and the clamp ring to squeeze another .0065" into the rubber doodad. I am using them all.
On 17/02/2004 Al Smith opined:-
It will most likely be as a result of some oxidation around the display connections. The PCB will have a series of pads under the display carrying the signals to the LCD. The link from the pads to the LCD is via a thin conductive rubber linking strip.
Try very gently cleaning the PCB connections, the rubber strip faces and the underside of the LCD display.
On Tue, 17 Feb 2004 11:02:51 GMT, Harry Bloomfield Gave us:
Very good call.
It is typically called a "zebra strip" and is a strip of insulative plastic interspersed with stripes of conductive rubber.
This allows for a flexible connection between the sometimes jarred display and the PCB. Cleaning the glass face of the LCD panel and the pcb at those locations and the strip will likely alleviate his woes.
Part 1
Part B
For some reason, I proceeded on without checking after Part 1.
Anyway, use alcohol on these strips? These strips worry me. A strange technology.
I'm a mechanical, but I used to work at Westinghouse. The wacko electricals there used to use an eraser to clean contacts. I converted them to a superior eraser -- Pink Pearl. I don't know if they make them anymore, But, I have digressed.
The strips are OK for alcohol?
Then, clean the edges of the
DarkMatter just about managed :
It could equally well be residue from the flux in the bottom of the drum, up to a double heavy pair of doors, with the new moderated version of leaks.
I wouldn't be able to try it.
On Tue, 17 Feb 2004 16:06:40 -0500, "Al Smith" Gave us:
Should be no problem.
Tell us how to solder to glass, and you'll make millions. :]
This is a cheap, effective solution to several electrical and mechanical issues surrounding LCD display panels or "read outs".
Very cheap. Can't be beat any time soon, in fact, IMHO...
When they start putting single chip blue tooth on a die that fits inside LCD panel layers, then we can have stand alone displays. Still not cheaper tho. As it stands, however, they need to be able to take flexure independent of the main PCB, and not apply stress to the LCD panel when it is experiencing pressure in various planes as part of its operating norm, as this fractures the glass. A common problem in the early days. It must also maintain the electrical impulses, if any, and a return path for them.
I thought it was one of the most innovative ideas I'd seen, those many years ago, when I first happened upon them in $9.00 calculators.
I started on old contacts type pinballs. The FIRST lesson taught is about contact care and maintenance, and what NOT to do.
Still there are bona fide products for the purpose, these days.
Yes. Most polymers are, however...
One or two drops of dish soap in a cup of water should be enough saponifier to clean it, if you are worried about using the IPA.
Most assembly shops use 99% IPA, and most homes have 71% typically.
Anyway, if you use the very lightly soapy water, rinse it in some warm distilled water (an absolute requisite must!), and let it dry out for an hour or two... Most of the products we buy these days were done on water soluble flux hardware, and aqueous wash. Though the LCD panel did not go through any such processes. This makes me wonder if touching the LCD panel edge with any liquid would be wise, or if the discoloration might not be leeching into the panel layers.
Naaahhh... It's the zebra strip. The glass is sealed... clean it.
Use a cotton swab and IPS (alcohol) or the soapy water and distilled afterwipe on the LCD as well. If you use the water, make sure to let it dry for a few hours or bake it at about 120 F for 20 minutes or so.
Must be dry. Then, the carburized rubber strips will conduct from the PCB pads, up to the LCD fingers via the little carbon resistors that the zebra strips make up. Doesn't take much electrical pressure to change the state of those segments.
Potato watches work on microamps. :]
On Tue, 17 Feb 2004 04:41:17 GMT, "Louis Bybee" Gave us:
Probably only to the original purchaser, however. At least that is typically how the policy goes.
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