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Paper Shredder S421 Not Working Repaired

By on June 19, 2020
paper shredder repair









As the lockdown is bit relaxed and offices are allowed to open with minimum possible staff.  I started attending the office.

paper shredder repair

The other day when I was sitting in my cabin our Housekeeping person came to me and told that small paper shredder of the office is having some problem, it is not working.

I asked him to call the technical department and get it checked.

After about an hour I got the call from the Technician that the paper shredder needs to be sent to the repair center but unfortunately they are closed due to lockdown.  He also informed me that paper shredder is not coming on while supply is connected to it.

I told him to wait, I am coming there.  When I went to the Technical department and saw the system, I immediately understood that waste bin is removed so the micro switch which gets operated when the waste bin is placed,  is not activated, that’s why power is not reaching to the motor.

I pressed the micro switch with screwdriver.  But to my surprise paper shredder motor started rotating continuously.  This should not happen until paper is inserted inside for shredding and photo sensor diode is obstructed.

I tried once again but same the motor kept rotating without cutting off.

My idea behind telling all this story was to give you the brief idea how the things started.

Now being an engineer I did not control myself and asked the technician to open the paper shredder and remove the control card with all attached cables except the mains In and out from the card.

The controller card is built with transformer less supply converting Ac 220 Volt to DC 12 Volt by using capacitor and resistance with diodes.  The dual op amp LM358 is used as comparator to control the motor supply of 220 volt in forward and reverse direction with the help of 2 relays.

When I brought the controller card on my test bench and connected AC input and bulb at output for forward motion of motor.  After keeping IR led and sensor face to face, when I switched on power supply to the board, the Bulb came on, while it should be off.  That means the forward relay is coming on due to some component failure.

how to fix paper shredder

On further check I found that, the base of the Relay driver transistor is getting voltage from the forward and reverse switch board.

paper shredder circuit board

As there are only few components in this FW & Rev Switch board, I started a cold check of the components.

You will be surprised to know that the forward switch Normally Open contact was showing 377 ohms, just like short from inside.  It should be open.

checking paper shredder

The switch is Non Lock 6 pin momentary Push Tactile Switch as given in the below diagram.

component layout

The circuit diagram of Forward & Reverse Board is given below for reference.

hand drawn circuit schematic diagram

After removing and cleaning the switch with IP Alcohol, I checked the switch for any short but it was showing open.  After that I soldered it back to the board.

how to repair paper scredder

After connecting back the switch and checking with multi meter, once again to ensure it is not showing any resistance now.  It was fine and showing open.

I connected the power supply to the board and testing lamp to the forward supply output point and checked.  It was working fine.  This time lamp was off even the power was connected and Green LED was on. Then I removed one of the the IR sensor LED and kept it aside.  The Lamp came on.    Mission accomplished.  Please see the below photos of its working.

fixing paper schredder

how to fix and repair paper shredder not working

Kishan Singh Rawat

This article was prepared by Kishan Singh Rawat, a Telecom engineer and electronic enthusiast with more than 35 years of experience in Telecom / Broadcasting industry, residing in Delhi, India.  Presently working as AVP in renowned News Broadcasting Company of India.

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You may check on his previous repair article below:




  1. Parasuraman S

    June 19, 2020 at 9:31 pm

    Excellent hunting service! Well presented and thanks for sharing!

  2. Albert van Bemmelen

    June 19, 2020 at 11:15 pm

    Good to know what components are used inside these shredders because I own one similar that still works but one day may need service too.

    About covid-19 and the lockdown situation in India may I ask if there already is some light at the end of the tunnel?
    I ask this because on 1 march and a second time on 22 april 2020 I ordered a book at an Indian bookstore (first time at, second time from Bookvistas) online. Since still nothing is delivered after being paid many months ago and endless waiting I hope the waiting and the epidemic ends soon. Thanks for sharing!

  3. Humberto

    June 20, 2020 at 2:04 pm

    Good repair Sir.


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