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Paper Shredder problem

gears47

May 12, 2020
32
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May 12, 2020
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My uchida shreddy, model UT-22 paper shredder, stopped working in the forward motion but runs when the reverse button is pressed.
I checked the Auto/Stop IR Photodiode and IR Transmitter Photodiode and found both operating correctly. When the auto/stop is activated you can hear the 12vDC relay chatter. This relay when activated completes the circuit to the starting capacitor. I checked the the 240Vac Transformer, the output measured 14.3Vac to the rectifier circuit. The output of the rectifier measured 6.37Vdc, which is too low to activate the 12Vdc relays. I am not sure if the main transformer is the culprit or if I have missed something. Any advice as to what you think is the problem would be appreciated. I have attached photos of the control board etc.
Regards Gears47.
 

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Bluejets

Oct 5, 2014
7,050
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the output measured 14.3Vac to the rectifier circuit. The output of the rectifier measured 6.37Vdc, which is too low to activate the 12Vdc relays.
Correct......so one or more of the diodes in the bridge are faulty.
Remove and test.
 

73's de Edd

Aug 21, 2015
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Aug 21, 2015
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3,636
Sir gears47 . . . . .

The output of the rectifier measured 6.37Vdc, which is too low to activate the 12Vdc relays.

True . . . . . a possibility . . . . . with one diode going open circuit . . . .but I would be equally suspect of the MAIN filter E-cap having gone w-i-m-p-y , after its extended time of use.
It is the LARGEST pale grayish blue E-cap, located nearest to the power transformer.
Its output additionally passes on down to the 7805 . . . regulator I.C. at the end . . . . .to then come back and get filtered by the BLUE E-cap beside it, as a 5 VDC supply for the 2 T T L and one quad section linear chips on the board.
Meter across it and take DC voltage reading while someone activates a paper entry, to see what its supply voltage then changes to.

I perceive of the normal motor run relay to be the one closest to the 7805, with the reverse relay being the other one.
Also I see the board mounted
RED push button switch, as being the paper jam, reversing switch . . .right ?

Do you have a white+ yellow wire, naked butt splice pair of the photo cell or LED power , that is neither being staggered apart nor insulated ?


Pee Ess . . . . .
Having accounted for all of the circuitry dee-sign, I'm still stymied by the presence of that Pee Cee Boards other ends second clone transformer?
Photo resolution is not good enough for its foil trace, path tracking . . .plus . . .
STINKING . . .GREEN resist being used on a GREEN board.

73's de Edd . . . . . .

shy-fart.gif
 
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gears47

May 12, 2020
32
Joined
May 12, 2020
Messages
32
Sorry for the delay in replying. I removed the 1N4007 diodes and tested 3 were okay, 1 had a lower reading to the others. I removed the E-cap and tested it. It was marked 25v 100uF, when tested using a capacitor multimeter it read 13.26nF (.13uF). I replaced all the diodes with new ones and a new 25v 100uF e-cap. Tested and now have 15.30Vdc and 5.05Vdc where required. I tested the reversing button and found that the relay near the main transformer activated and the motor ran smoothly with no relay humming noise. I then tested the auto/stop and found that the motor still did not run. After checking the circuit, I find that the relay closest to the 2nd transformer has to be activated. When tested I have +12Vdc to both sides of the relay coil. The -12Vdc is supplied via the auto/stop circuitry. I removed and tested the infrared LED which appears okay. (Photo attached) and when introduced to the phototransistor, nothing happens, yet when parted the motor makes one half turn. That 2nd relay needs to be activated to supply the 240Vac to the 2nd transformer to activate the motor in the forward motion. In relation to the red+ blue wires and white+ Yellow wires the splice is insulated with clear heat shrink. I have attached some new photos of the end of the board where the se3cond transformer is located. Some of the photos are taken with a light source behind the board. The red button is for reversing when there is a paper jam.
 

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73's de Edd

Aug 21, 2015
3,636
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Messages
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Sir gears 47 . . . . .

CHICKEN LITTLE WAS RIGHT ! . . . . . THE SKY WAS FALLING ! . . . .
with a deficient discrete bridge diode and a defunct main storage cap falling HARD onto the ground.
Now lets more fully explore, and see why the shredder motor is not running on a paper sheets entry.
Initially . . . . . with a mark up of . . . . .
PHOTO REFERENCING . . .
1716104256317.png
or . . . .DIRECT HOT LINK

Initially, lets check out that left photo at its top and see 8 visible solder joints across the top . . . as . . . 1 space2-3-4-5 space 6 space 7 long space 8.
Now solder joint coverage on #1 looks adequate, but grab a / each wire and push in-pull out on and rotationally wiggle the wires on all of the other joints, while CLOSELY observing on the solder blob side, to confirm that there are being no floating solder joints. Do a REFLOW /REWORK with fresh solder if joints are questionable.
The two shades of PALE BLUE foil path markups, revealed to me that 240 VAC power goes to the left, in addition to the main power transformer PLUS your photo showing a 3 wire bi directional motor connection with assist of an AC run capacitors presence.
This means that the left mystery transformer . . . . is actually providing a reduced . . .MOST LIKELY . . . 24VAC to run the shredder motor . . . . that mystery solved.

MARKED UP PHOTOS POINTS OF INTEREST . . . .
You say . . . . .
I tested the reversing button and found that the relay near the main transformer activated and the motor ran smoothly with no relay humming noise.

I say . . . . .

So o o o o o I assigned that right side BLUE relay, as that function, leaving the other left side BLUE one as being the one that needs to be activated, in order to operate the shredder normally, after any scrap papers insertion.
Associated parts are the RED star, back EMF quenching diodes are across each relays coil.
Take note of the GREEN and BLUE rectangle marked relay driver transistors facing each other. I HIGHLY suspicion that each transistors required individual base drive is coming in from each of the two separate 4.7k resistors.
I also marked them in on the FOIL photo to the left. Blue and Green connecting lines go from resistors to bases on the right photo. Other transistor element connections fall into place, with my suspicion of the transistor center pin being collector and going to its relay coil, with the transistors far end pin being emitter and going to ground.
Will you positively confirm this for me ! ***

POWER SUPPLY MARKUPS . . .

VERY top input is constant 240VAC to power transformer primary if the units master power switch is on.
Secondary AC from transformer goes into discrete 4 diode FWB at central diode points and is DC collected at left ends Red + rectangle and right ends Black - rectangle and sent to your NEW 220 ufd main E-storage cap.
12VDC also passes to far right to 3 terminal +5VDC regulator and routes back as +5VDC regulated at smaller BLUE E-cap, just below the earlier MAIN one.
If there was no insulator used at the 3 term regulator, its finned heat sink might be more convenient to clip a meter ground lead onto, instead of the FWB - diode lead pairs.

THE OPTICAL INTERRUPTER PAIR . . . .

YOU PUT A PAPER INTO THE FRONTAL SLOT FAR ENOUGH, THAT THE PAPER THEN BLOCKS THE LED to SENSOR BEAM AND THE SHREDDER MOTOR ACTIVATES AND PULLS IT IN FOR SHREDDING.

One of your photos has shown us an operational LED emitter. Circuit wise, its having a . . . . 12? or 5 ? VDC supply passing thru a voltage dropping / current limiting supply resistor to the LED and the other LED lead to ground.
But now, we don't know if the other half's . . . . receptor / sensor. . . . is being an active or passive unit .
E.G. . . . being . . . self voltage generating, like a solar cell . . . . . . . . or variable resistive, like a CdS cell.
We would expect one receptor / sensor lead to be grounded also.

Look at the 4 Pin connector that the optical interrupters pair of wires connect into, its location is being sandwiched between the discrete FWB diodes and the 74LS02 logic chip. I have already assigned 4 random numbers to it.
With a dead and un powered shredder unit, take ohmmeter in hand in its lowest ohm range and short probes together to take a dead short reading. Take note. Move to then ohmically testing between FWB diode negative pairs and the finned heat sink of the regulator, is there also almost 0 ohms there ? if so, the regulators finned heat sink is a viable alternate meter negative grounding connection also.
Now lets move back to the optical-interrupter pair and keep of the ohmmeters probes on ground ad see if 2 of those 4 pins are ground connected ? Report back.
Next look at the small resistor just to the right of pin 4 of that connector. In that boards linear layout . . . .isn't it logical ? foil flow path sequence such that the right resistor lead goes to +5 or +12 VDC power supply and the left
resistor lead feeds the pin to the LED emitter, with the LED's other lead being grounded. Sort of expecting pin #4 to be receiving voltage reduced and current limited power and pin #3 to be grounded .
OF COURSE . . . . You already have visual confirmation of the wire color coding of the 2 wire pairs connecting pins.

That then leaves pins #1 and #2 to relate to the sensor connections, if one of those pins has already identified as being grounded then the other has to be the "active " connection.
Then we have an UBER HIGH interest, in the sequential circuit routing of that "active" voltage level thru the TTL and linear circuitry, until it finally provides base drive to the GREEN relay driver transistor-close relay-run shredder motor.


FIRST POWER UP ANALYTICAL TESTING . . . . .

Place meter negative test lead to a confirmed ground and then set to + DC Volts range . . .expecting <20VDC . . . .+ meter probe goes to right resistor lead of the resistor just to the right of 4 pin O-I connector.
What is that supply voltage ? then what is the voltage to the left lead of that resistor . . . .establishing Emitter LED Vf run spec.
Next points of interest would be the received base drive levels of the two relay driver BLUE and GREEN transistors.
Examine the left photo and see your now exposed RED paper jam electro-mechanical switch, it appears to have a left and right pole piece and a fixed single contact for each movable pole, thus making it a Double Pole Single Throw unit. On the left photo, just to the switches left, I have a vertically drawn in 4.7k resistor . . . also its ACTUALLY being present on the right photo.
Now what we want to do is use the same DC metering set up as was just used before.
We want a power up and take measurement of the DC voltage level in at the bottom lead of that 4.7k resistor . . .log down . . . and then on the top lead of that resistor. . . log down.
NOW monitor the bottom supply side of that resistor and press the RED switch and start reverse motor action and see if that voltage level pulls down, if so, log down.
Release the RED switch and move metering to the top lead of that resistor and log down its voltage supplied to the Blue transistors base.
Now press the RED switch an see what that voltage changes to log down and then hold the RED button down again to see if the lower leads supply voltage was pulled down, if so, log it down.
You now have some idea of voltage changes involved with the functioning Blue driver circuitry.
NOW . . .lets move up to the Green driver circuitry and see whats being amiss in that non working section.
Go thru the same testing sequence in monitoring across that twin 4.7k up at the Green line input to the base of the Green relay driver transistor.
The EXCEPTION / VARIANCE , this time will be the need to use an opaque piece of cardboard just inserted enough to block the beam of the photo-interruptor path instead the prior Red switch.
Initially take power in 4.7k resistor lead reading and also base of transistor lead readings and then just block the beam and take the same readings to see what the base drive voltage is being and if the supply side of the resistor pulls down and log down voltages.
You confirmed what was needed on the other working transistors base for relay activation. What voltage level is now being present on the inoperative Green driver stage ?
Finally monitor the left side of the resistors left end lead and then use the cardboard to block and unblock the beam to see if there is the synchronous response of an according . . . . . even slightest up and down voltage change.
If not, we will next be off on a sequential logic trail hunt.

BREAK-A-BREAK-A TIME . . . . .
To see if additional info is needed . . .feed back of voltage readings . . . . your answers

73's de Edd . . . . .

EatingPopcorn.jpg
 

gears47

May 12, 2020
32
Joined
May 12, 2020
Messages
32
To 73' de Edd. Thank you for your input. Hope you can follow my findings.
All solder joints 1 thru to 8 all ok. Pin 1 is the main transformer connection which is feed from pin 2 (240Vac active supply), Pin 2 is bridged to pin 4 supplying 240Vac active to the motor via the grey wire. Pin 3 is the 240Vac negative which feeds the main transformer, also the open contacts of both relays. Pin 5 is connected to the motor via the red cable and also looped to pin 8 which is connected to the motor starting capacitor and also to one of the primary legs of the second transformer. Pin 7 and pin 6 are bridged together with, pin 7 being connected to the motor starting capacitor and pin 6 being connected to the motor via the blue cable and is also connected to the fixed contact connection of the reversing relay (right side). When that relay is activated, it supplies the 240Vac negative to the motor and starting capacitor.

The second transformer receives the 240Vac negative when the relay on the left is activated.

The 4-pin connector for the optical interrupters that you have marked 1-2-3-4 have the following connections. PINs 1+2 are bridged and supplied +5.05Vdc.

Pin 1 (white wire positive) +Pin 3 (yellow wire) has the Infrared phototransistor clear transparent lens (ZD 1950) connected to them. Pin 3 then connects to the middle resistor (1kohm) next to the 2nd transformer. The voltage measured pin 3 to earth is 0Vdc, with the transmitting LED uncovered or covered. I know the transmitting LED is working but not sure with the phototransistor. I have reversed the connections of the phototransistor but still get the same readings. Have measured the voltage to both legs of the phototransistor to earth and they are the same +4.98Vdc. Measured the anode leg (white wire) to the cathode leg (blue wire) with a reading of +1.75dc when the beam is broken and 0Vdc when beam is unbroken.

Pin 2(blue wire positive) + Pin 4 (red wire negative has the Infrared Transmitting LED (ZD1945) connected to them. The voltage measured pin 2 to earth = +5.05Vdc. Pin 2 to pin 4 (right side of the resistor) = +1.203Vdc. Pin 4 to Earth (left side of the resistor) = +3.85Vdc.

4.7k resistor to the left of the reversing switch readings are: at the bottom of the resistor to earth is +0.56Vdc, at the top of the resistor to earth is +0.61Vdc.

The voltage readings requested in relation to the relay driver transistors. Right side of resistor to earth = +3.51Vdc. Left side of resistor to earth +0.75Vdc. First leg of transistor marked green to earth +0.75Vdc. Centre leg of same transistor to earth +0.12Vdc. leg 3 of same transistor to earth +0Vdc. First leg of transistor marked red to earth +0Vdc. Centre leg of same transistor to earth +0Vdc. Leg 3 of same transistor +0.56Vdc. Bottom side of 4.7k resistor to earth +0.56Vdc. Top side of 4.7k resistor +0.63Vdc.

Voltage readings at both 4-7k resistors with reversing switch activated: Resistor to the left of 4-pin optical interrupters connections show: left of transistor = +0.77Vdc and +0.57Vdc at the right side. Switch activated right side read +03.50Vdc and +0.16Vdc on the left. Readings on the 4.7k resistor to the left of the reversing switch read left at the bottom +0.56Vdc and at the top +0.69Vdc at the top with the reversing switch activated or not.

Carried out the same test at both resistors by blocking the beam of the photo interrupter. There was no change in the readings with the beam interrupted or not.

Voltage measurements to reversing relay coil to earth = Left +0.12Vdc Right +13.45Vdc when relay activated and both sides +0Vdc when relay not activated.

Voltage measurements to the relay required to activate transformer 2 = Left +13.47Vdc Right +0.12Vdc when not activated. Have not been able to activate that relay.

I don’t know if the problem is in the relay driver transistors or in photo transistor. I have sent another photo of the infrared LED in its housing, as well a print showing the output (Cathode) leg for the phototransistor ZD1950.
 

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