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Troubleshooting an optical encoder

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OM222O:
Hello
I have a 600 pulse per revolution optical rotary encoder which I bought a few months back. I first thought it's dead on arrival as it was outputting no signals (connections were correct). I decided to check it with an oscilloscope a few days later in our uni lab and it was magically working fine  :phew:
I just thought there might have been a bad connection or something the first time around. I played with it for a few hours and got everything to work, even used a trick to get 2400 pulses per rev which was really nice. I didn't have all the parts I needed for the project so I put the encoder aside. Today I finally have gotten the rest of the project working (mechanical side) and went back to use the encoder, but to my surprise, there was no signal on the output again! I have ordered a new replacement which can take a few weeks to arrive so I want to troubleshoot and fix this one if possible. I searched a bit but couldn't find any detailed description or PCB layout or schematic or anything about how the device actually works (some of the chip markings are removed which is super annoying  :-//). if anyone has any information about how these devices work or has a schematic of them, it would be very helpful. I think it's an analog light sensor (similar to LDR) which is then converted to digital signals using a voltage comparator or similar but that's just my theory. Thanks a lot everyone

jmelson:
Many encoders need a "pull up" resistor to some positive logic level, like 5 V.  Just a 1 K Ohm resistor from the +5 supply to the outputs will do it.
Otherwise, just check that the power and ground are connected to the right pins.

Jon

OM222O:
Thanks jon
Although I didn't have any pullup resistors in the lab a few months ago, it had worked flawlessly, maybe I just got lucky.

I connected two 1k pullup resistors to VCC (5V) and it seems to have fixed the issue for only one of the phases (phase B or the green wire) but there is still no response from phase A. It seems unlikely but I can't think of anything else at this point. which kind of renders it useless for the application I had for it. I don't have many different value resistors but 10k didn't seem to fix it either ... there's a chance I might have killed one of the phases? (I never connected anything backwards, and did not connect the phases to any supply rail (VCC or GND) directly, connections were always correct and outputs (phases) were only connected to input pins of arduino). If anything could die, I'm guessing it would be the output pass element? the sensor itself is unlikely to die in this situation but still possible. Any ideas on how to check what's wrong with it?

OM222O:
Upon further inspection, the chip markings are not removed, just really hard to read (needs the tongue in the right angle   :-/O). The soldering quality is also terrible and there is white powderi stuff which I assume to be a flux of some sort (didn't completely clean with 70% IPA) with really excessive solder on some parts and practically non on the others.


I fixed the connection on the 3rd pin thinking that was the issue, but nope! phase A (white) is stuck in pullup mode ... the circuit for 2 phases doesn't seem to be identical either (one of them has a diode on the output, one of the goes to a capacitor while the other one doesn't etc)


The big 3 pin THT package is a TL750 (750l05C) LDO.
The small sot 23 packages are also marked Y1 which I googled to find the SS8050 NPN transistor which sounds about right as an amplifier (or switch) in this case.
if anyone can make sense of why the phases are different and how they work, please let me know!

Kasper:
I think I wrecked an encoder once by using too small of a pull-up resistor and running too much current through it.

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