Optical Encoder diagnostic - Page 1
Forum section: electronics / repair

author: adel
author_rank: Newbie
timestamp: October 01, 2014, 08:01:43 pm
content: 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: AM26LS31C2- Encoder Sensor : Avago H97313- three SMD cap + 2 SMD resthe motor is 36V DC - 3000 RPM & Encoder : 1000P/Rthe question is , how could i diagnosis the error part to replace it and get the motor run correctly again ? any suggestions could be help

author: SL4P
author_rank: Super Contributor
timestamp: October 01, 2014, 11:10:24 pm
content: The encoder consists of1- IC: AM26LS31C2- Encoder Sensor : Avago H97313- three SMD cap + 2 SMD resA 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 gremlinsIC - 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.

author: adel
author_rank: Newbie
timestamp: October 02, 2014, 06:35:09 pm
content: SL4Pthanks for replay , could you please explain the purpose of the IC :AM26LS31Cand how could i tested it with only AVOmeter available ?

author: adel
author_rank: Newbie
timestamp: October 03, 2014, 06:07:48 pm
content: 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 ?

author: SL4P
author_rank: Super Contributor
timestamp: October 04, 2014, 10:17:31 am
content: The IC is simply a 'diffferential' line driver... put a high or low on the input(s) and see the output(s) change state(Datasheethttp://www.ti.com/lit/ds/symlink/am26ls31.pdf)Youmayhavecookedthe sensor LEDs with 5V directly into the Vcc pins.The datasheet specifies3V3(oops)(http://www.avagotech.com/docs/AV02-1057EN)I expectHEDS-9731 pins 2 & 4 (outputs)of each sensor go to...AM26LS31C (input) pins1A/2A/3A/4A ...TheAM26LS31C output pins1YZ/2YZ/3YZ/4YZ - head off to the central controller.(AM26LS31C pin # depends onwhichchip 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 ineachsensor part. (The datasheet explains best)

author: SL4P
author_rank: Super Contributor
timestamp: October 11, 2014, 04:48:55 am
content: You're welcome.