It’s a fact that you can repair as many multimeters with a bottle of isopropyl alcohol and some Q-tips (cotton buds), as you can with a soldering iron. In many cases, malfunctions can be fixed by careful disassembly and cleaning of affected parts. Only simple tools and materials are required, but caution is recommended so as not to damage any of the components or plastic bits.
[Click on any of the following pictures in this article for a larger view. All graphics used in this article are also available as an image gallery.]
This Fluke 83-III looks like a prime candidate for this sort of low-tech repair. It basically works and seems to be calibrated correctly, but occasionally when set to measure Ohms, the display will flicker a bit and only display “OL”, regardless of whether the leads are connected to anything, or even shorted together. A slight tap on the rotary switch will cause it to start working correctly again. Odds are, there’s a minor problem with the internal switch contacts.
[To my knowledge, this procedure applies to any of the generation-I and generation-III 80-series meters.]
To begin the disassembly, there are three self-tapping screws that hold the outer case together. After removing those screws, gently pull apart the two halves of the case at the bottom near the input jacks. The top edge will eventually unsnap. The front cover, back cover and internal meter assembly will separate cleanly into three pieces. We’re interested in the meter assembly.
Remove the one screw on the back side. This releases the two halves of the shield. The rear half of the shield has two T-shaped tabs at the top edge that interlock with the circuit board. Mind these tabs when pulling the shield off, and do not break them. You will find the piezo beeper element affixed to this part of the shield.
The front half of the shield contains the LCD assembly and is held onto the PCB by four barbed clips. These clips are very fragile!
The LCD is connected to the PCB via two elastomeric connectors (often called “zebra strips”.) When these strips do not make good connection with the PCB, some of the LCD segments may disappear or look faded. Do not touch the surface of these connectors, as skin oils can inhibit connectivity. They can be cleaned with isopropyl alcohol (IPA) and a Q-tip.
On the back side of the PCB you will find a black rotor, which is part of the ‘code switch’. This switch is responsible for turning the power on, and providing a signal to the micro-controller indicating which function has been selected.
Use non-metallic tools to gently pry the rotor from the hub. When prying be careful not to apply too much pressure to the SMD resistors, as they can break. The rotor should pop off with gentle pressure. [These are "spudgers", available often as part of cell-phone/laptop repair tool kits.]
The code switch tracks in this case do not look too bad. Use Q-tips and alcohol to clean the tracks. NOTE: On the original 80-series meters, these switch tracks are not metal, but are made from a black conductive material called polymer thick-film (PTF). This material is somewhat fragile, so use caution to avoid damaging it, and never use anything abrasive.
In some cases such as this one, I find a fiberglass scratch brush to be helpful without doing any damage (if used sparingly.) A light brushing followed by thorough clean-up with Q-tips and IPA, restores these contacts back to good condition.
Re-assemble the switch by gently and evenly pressing the black rotor back onto the hub. Gently press the LCD/front shield assembly back onto the PCB, making sure that all four clips are secure. Then attach the rear shield by aligning the T-shaped tabs on its top edge and re-installing the screw.
Before putting the case back together, position the switch rotor to the OFF position as indicated by the pointer. Also place the knob in the OFF position. This is important and will ensure correct alignment and operation of the switch.
A small dab of petroleum jelly on each of the self-tapping screws will help them to turn easily and help protect the plastic screw posts from breaking. Try to make sure the screws seat properly in the original threads and avoid cutting new ones.