Originally Posted by
blackcat4866
Sorry, yes, I use the meter every day.
I'll do this by categories:
Motors:
There are very few motor failures, and they're usually fairly obvious (like the motor doesn't turn). Motors with 4 or more wires and not a circuit board built onto it are pulse motors which have multiple sectors. Each sector is a continuous loop that advances the armature a certain number of degrees. For example a (6) wire pulse motor has (3) sectors, each advancing the armature 120 degrees of a rotation. Each sector is a low resistance loop, close to (0) ohms and infinite to the motor housing.
Motors with a circuit board mounted to them are controlled by a driver circuit, and an not so easily tested with a meter.
Motors with two wires (often red and black) are typically 24vdc. You can read resistance across the wires. As you rotate the armature the resistance will alternate open, closed, open, closed. You can check for a supply voltage. Keep in mind that most copier circuits are ground switching. That means that the +24vdc is always present at the motor, and the main board starts the motor by connecting the ground (same as frame ground).
The good news is that most copiers have a test mode to run individual motors on demand.
Solenoids:
Most solenoids operate on 24vdc. It's a continuous coil with a ~80 ohm resistor in series. You can test it for resistance across the two wires (~80 ohms, but don't get hung up on looking for a specific value, just not infinite), and resistance from the coil to the solenoid mount (should be infinite). You can also test the DC voltage same as the 24vdc motor.
On a side note there are a few exceptions. Occasionally you'll come across a solenoid with multiple coils, sometimes a diode in circuit (which means it will only show resistance in one direction), and sometime a rare earth magnet built in.
Solenoids can fail in four ways:
1) the sound damping foam pad gets sticky, releasing slowly after a while energized.
2) the plunger magnetizes, releasing slowly or not-at-all after a while energized.
3) the coil opens to infinite ohms
4) somebody oils the plunger (never oil a solenoid, clean with alcohol only)
The good news is that most copiers have a test mode to run individual solenoids on demand.
Clutches:
Most clutches operate on 24vdc. It's a continuous coil. You can test it for resistance across the two wires (~80 ohms, but don't get hung up on looking for a specific value, just not infinite), and resistance from the coil to the solenoid mount (should be infinite). You can also test the DC voltage same as the 24vdc motor.
The good news is that most copiers have a test mode to run individual solenoids on demand.
Photointerrupters:
Most have (3) wires:
1) +5.0vdc
2) frame ground
3) sensor output
First: on low DC volts range connect black to frame, then check each of the sensor leads with the sensor blocked then unblocked. The pin that stays at 5.0vdc blocked and unblocked is the hot. The pin that stays at 0vdc blocked and unblocked is the frame ground. The pin that changes when you block/unblock the sensor is the output. Here's where there's some variation:
Some photointerrupter's output are close to 0 vdc blocked and close to 5.0vdc unblocked
Some photointerrupter's output are close to 5.0vdc blocked (triggers around 3.5vdc) and close to 0 vdc unblocked
Mainly you're looking for the change.
Now the best part: most copiers have a service mode that will allow you to test photointerrupters. What that service mode does not tell you is the actual output (your sensor peaking at 3.6vdc won't always properly trigger the board).
Thermistors:
Thermistors are measured in resistance at a high range. This is another case where the actual resistance value is not as important as seeing ~400K ohms at room temperature, and about 250K ohms at finger temperature. At actual fixing temperature the thermistor will be down in the hundreds of ohms. Just watch for a dead short or open circuit.
Thermostats:
Thermostats should be 0 ohms at all times. It's rare, but I have seen thermostats the start to increase in resistance as the load of the heat lamps is applied. The way to test for this is heat up the fuser and re-check the thermostat when full hot.
Notice that you can test most of these components in service mode. That's great for a catastrophic failure, but for an intermittent issue it won't always help you. =^..^=
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