Electronics > Repair

Optical Encoder diagnostic

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adel:
Hello every one , greetings from Egypt , I have a servo motor controlled the x-axis motion of a wide format solvent printer , yesterday , it stops suddenly and it was free to move , i replaced it by a new one and the printer worked fine , Now i want to get it working again ;) , the encoder consists of 1- IC: AM26LS31C
2- Encoder Sensor : Avago H9731
3- three SMD cap + 2 SMD res
the motor is 36V DC - 3000 RPM & Encoder : 1000P/R
the question is , how could i diagnosis the error part to replace it and get the motor run correctly again ? any suggestions could be help :)
 

SL4P:
The encoder consists of
1- IC: AM26LS31C
2- Encoder Sensor : Avago H9731
3- three SMD cap + 2 SMD res

A simple setup.

Most likely culprit wil be the sensors - stimulate the LED, and see if pulses come out of the phototransistor when you interrupt the optical path.  Maybe fluff or dirt.

Resistors & Caps - pullups and decoupling... a multimeter should identify any gremlins

IC - RS422 driver - measure the differential outputs to identify the oairs are working.

An unusual topology - seems like they're simply pushing the encoder outputs directly across the differential (422) pair to a processor somewhere else.

Luckily your module is out of the device, so isolating the individual parts should be straightforward.

adel:
SL4P
thanks for replay , could you please explain the purpose of the IC : AM26LS31C and how could i tested it with only AVOmeter available ?

adel:
I checked the Optical Encoder Module " HEDS-9731 " , and when i tested it , i connected 5.12v to Vcc and 0v to GND , the output from Channel A and Channel B is always 5.02 v even when i close the LED path , whats the problem please ?

SL4P:
The IC is simply a 'diffferential' line driver... put a high or low on the input(s) and see the output(s) change state
(Datasheet http://www.ti.com/lit/ds/symlink/am26ls31.pdf )

You may have cooked the sensor LEDs with 5V directly into the Vcc pins.
The datasheet specifies 3V3 (oops)(http://www.avagotech.com/docs/AV02-1057EN)

I expect HEDS-9731 pins 2 & 4 (outputs) of each sensor go to...
AM26LS31C (input) pins 1A/2A/3A/4A ... 
The AM26LS31C output pins 1YZ/2YZ/3YZ/4YZ - head off to the central controller.
(AM26LS31C pin # depends on which chip package is used)

The sensors are spec'd at 3V3, while the interface driver is 7V ??
This suggests either separate +V rails to the module, or perhaps the sensor's 'emitters' are wired in series (~6V6) to 'handle' the same supply voltage).

Just break the problem down into separate blocks - each is very simple.
Blocking the optical path should see the sensor outputs alternately go 'high' & 'low'... there are actually two optical paths in each sensor part.  (The datasheet explains best)

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