ITT MX20 Multimeter Teardown and refurbishment

A friend gave me an old defective ITT MX20 Multimeter.
The multimeter is still currently sold under various brands. It’s a very rugged, IP67, electricity oriented multimeter.

The multimeter, now in working order.
The multimeter, now in working order.

Removing the front panel reveals the IP67 rubber seals.
Removing the front panel reveals the IP67 rubber seals.
Behind that seal, we find the two AA batteries and the two HRC fuses compartment.
Behind that seal, we find the two AA batteries and the two HRC fuses compartment.
Finally, the rear panel is the way to open the meter. No screw here, it's simply clipsed... Notice the white rubber seal though.
Finally, the rear panel is the way to open the meter. No screw here, it’s simply clipsed…
Notice the white rubber seal though.
As you see in next pictures, the main problem in this meter was a leaky battery. Corrosion is present on the back cover shielding foil. No worries.
As you see in next pictures, the main problem in this meter was a leaky battery. Corrosion is present on the back cover shielding foil. No worries.
Banana posts are directly bolted onto the PCB. Too bad, no shake proof washers. And fortunately, as the batteries are just behind, the PCB has no sign of corrosion.
Banana posts are directly bolted onto the PCB. Too bad, no shake proof washers. And fortunately, as the batteries are just behind, the PCB has no sign of corrosion.
Nice and clean PCB layout.
Nice and clean PCB layout.
The corrosion from the leaky battery. One of the two springs is badly damaged.
The corrosion from the leaky battery. One of the two springs is badly damaged.
Corrosion on the other side. The MX20 is built in a dual PCB layout.
Corrosion on the other side.
The MX20 is built in a dual PCB layout.
The main board is on the back. It's a mix between surface mount and through hole components.
The main board is on the back. It’s a mix between surface mount and through hole components.
This side shows the current shunt resistor and the two PCB to PCB interconnect system. Two simple 2.54 mm header connectors. They doesn't fit completely inside...
This side shows the current shunt resistor and the two PCB to PCB interconnect system. Two simple 2.54 mm header connectors. They doesn’t fit completely inside…
The two boards disassembled. Piezo buzzer sits under the LCD screen, close to the main chip. Just one big chip and a couple of passive components.
The two boards disassembled. Piezo buzzer sits under the LCD screen, close to the main chip. Just one big chip and a couple of passive components.
A closeup on the main chip. It drives directly the LCD screen.
A closeup on the main chip. It drives directly the LCD screen.
And a closeup on the main switch contacts. On the left the input resistance for the voltmeter. On the left, the current shunt resistor for the amp meter.
And a closeup on the main switch contacts. On the left the input resistance for the voltmeter. On the left, the current shunt resistor for the amp meter.
And finally a closeup on the... input protection. I'm not an expert, but it seems there's no MOV, no diode bridge... I don't know what's R01...
And finally a closeup on the… input protection. I’m not an expert, but it seems there’s no MOV, no diode bridge… I don’t know what’s R01…
The battery compartiment, cleaned. Corrosion removed. Luckily the damaged spring isn't avoiding a good contact from the battery.
The battery compartiment, cleaned. Corrosion removed. Luckily the damaged spring isn’t avoiding a good contact from the battery.

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