Hi
I have a Fellowes PS-62C shredder like this:
Suddenly, without warning, the sensor which detects a sheet of paper stopped working, so that the shredder is always on (unless I switch it off manually). The sensor looks like some kind of IR thing. I've cleaned it, but that hasn't helped.
Any ideas?
Cheers!
Martin
These sorts of sensors typically have an IRLED and photodiode. If transmission, they will be on opposite sides of the paper path. If by reflection, it will be a single sensor assembly. If you can identify the photodiode pins and disconnect one, that should stop the shredder if it's a sensor problem.
Can you take pics of the sensor?
--- sam | Sci.Electronics.Repair FAQ:
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transmission,
disconnect
Hi Sam,
I can't get a good pic of it, but it would seem that on both sides of the paper path there is something resembling an LED, although each one looks slightly different. There is no reflector involved so far as I can tell.
What I would like to do is get the sensor working again. The shredder is designed with an "on/off" switch. When the switch is set to on (and the sensor is working properly) it is in fact in standby until triggered by a sheet of paper detected by the sensor. With *my* shredder on that setting the motor runs continuously. However, I can easily stop it just by manually flicking the switch to off. I just like having the sensor working.
Cheers!
Martin
Instead of the sensor, I would look at the triac or relay that drives the motor. It probably failed in the On state as those parts often do.
The sensor is just an IR LED. An easy way to test if it is the sensor is to shine a bright flashlight onto the non-IR LED. If it shuts off it is the sensor which can be sourced anywhere. If it doesn't shut off, it isn't the sensor. Sensors are a major problem with Fellowes & I always keep at least 6 sets in stock.
Cmart> Hi
LEDs are emitters of light, not sensors.
MBQ
Poor sensors perhaps, but the *do* work as sensors!
-- - René
it
it
They're not used as such in any sensible application.
MBQ
transmission,
be
disconnect
First test: Try shining a bright light into the area of the sensor, or directly if it's apart. Even with a filter to block visible, enough should get through and the machine should turn off. A good flashlight might do it. I doubt it's any more sophisticated than simply looking for light across the paper path.
If this works, then you should be able to identify the IR LED. Then, it's a matter of determining if the IR LED isn't working or isn't being driven.
If the test doesn't work, the sensor may be bad.
--- sam | Sci.Electronics.Repair FAQ:
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Well practically you would be ill advised to use a generator as an electrical motor but there is in essence no functional difference between the two. So with a LED a current leads to light being emitted, there is no theoretical reason why if I shine a strong enough light of the right wavelength on a LED I won't get a current out of it. In practical terms if I want to use my LED in this way I will get more efficent performance if I optimise it for this function. But this does not change the underlying reversibility of the physics.
Peter
-- Add my middle initial to email me. It has become attached to a country www.the-brights.net
They do work but rarely used in anything like this. Photodiodes are used with IR LEDs.
But a comment in another post that it may not be the sensor also needs to be pursued. That sensor drives a triac (probably) and they do fail shorted.
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Many thanks for all the advice. Mysteriously, the thing is now working again as it should. I guess it will probably go again soon, but now I know what to do.
Cheers!
Martin
Curiouser and curiouser - it was woking fine while the sun was shining into my study, but it stopped working again as the light began to fade indoors this evening. It works fine if I keep put my desklamp near it! I guess this does mean that the IR LED is failing. Or maybe it's just afraid of the dark, and likes to keep its motor going to scare off the monsters.
Peter Ashby inscribed thus:
Actually I have practical experience of this phenomena !
I used an LED as a noise source, and it worked very well, but had real problems suppressing the 50 Hz hum on the signal, until I realised that the hum amplitude changed when I stood between it and the fluorescent light !
--
Best Regards:
Baron.
Did you rule out that you were blocking a magnetic signal?
Peter
-- Add my middle initial to email me. It has become attached to a country www.the-brights.net
Or there is a dodgy connection, when the unit is warm the metal expands and makes the connection, when it cools the connection is broken. I had this with an incandescent bulb. It blew, but then it came back on then went off, then back on, then off etc. The filament had broken, when it cooled it contracted and reconnected, at which point it heated and broke the connection etc.
Peter
-- Add my middle initial to email me. It has become attached to a country www.the-brights.net
Yep, either the LED or the power source to it. Sounds like you're close.
You're right.... meant to say shine the light on the sensor. It's tough getting old and having brain farts and finger farts at the same time. Don't even have a dog to blame it on.
Csnipped-for-privacy@hotmail.com wrote:
Shining a moderate amount of focused light on e.g. a green led gets you way over 1 volt - enough to switch a transistor. Try it on a scope and be amazed.
If some Chinese manufacturer can save $0.01 by using a led rather than a light sensor - he will happily do that. There might be buying advantages to using the exact same led for illumination and detection.
-- - René
snipped-for-privacy@blueyonder.co.ruk (Peter Ashby) wrote in news:1i012q3.1a0ekg314xrqxdN% snipped-for-privacy@blueyonder.co.ruk:
....
Cool!
People are not very good at acting as a magnetic shield. You need a good conductor for an AC field and Mu Metal to block DC magnetic fields. [or a super conductor]
My ham tranciever was sensitive to AC magnetic fields. The VCO oscillator coil, a toroid, picked up the AC magnetic field from the tranformer in the power supply. This made a noticable hum modulation on received and transmitted signals. The manufacturing company has a mod kit available that replaces the toroid with a smaller toroid that is shielded.
While I was trouble shooting the problem, I found that my soldering station, which has a tranformer in the base, would also modulate signals. Moving my hand in between the radio and the transformer did NOT change the signal significantly. Therefore I doubt that the source of the ac that he was seeing was a magnetic field. Perhaps electrostatic, but I am betting that he found that putting a piece of black paper around the led fixed his problem.
-bz-
-- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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