help trouble shooting canon power supply

Discussion in 'Technical Repair' started by led_lights, May 29, 2018.

  1. led_lights

    Thread Starter New Member

    Jan 18, 2018
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    I have a pixma mx922 printer that was working fine then I went to print something else and the unit was powered off and have not been able to power on since. Im hoping it is just the power supply but would like to know for sure before I spend nearly 30.00 to purchase a new one. Also in the process of getting power supply open with out the proper bit i think I may have broken a small part of one circuit on the board. Maybe I can fix this with a jumper wire and maybe even fix this for a few dollars but more than anything I want to know if the ps is in fact my problem. Any help on where to test and what voltages I should get would be a great help. Going to post pics of this that should give info if not I can post the specs if pics are not clear enough. IMG_20180529_121927.jpg
     
  2. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
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    IMG_20180529_121846.jpg
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,402
    1,220
    Looks like the mains input filter snapped off, it can be resoldered back, is there about 250 to 350v dc across the large input capacitor .?
     
  4. dendad

    Well-Known Member

    Feb 20, 2016
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    Please be careful.
    Fixing power supplies like this is potentially leathal, more so if you don't know how to do it. To be a little safer, a mains isolation transformer is needed.
    An idea may be to look for a second hand printer on Ebay.
    Other than that, look for blown fuse and other parts.
    If you are going to work on it, pull the plug between tests and make sure the main filter cap has discharged before delving into it.
    Remember, mains can kill you.
    My advice is to not attempt a repair if you are unsure. Particuly if you can readilly get a replacement supply.
     
  5. Hymie

    Member

    Mar 30, 2018
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    Wouldn’t it be great if by just looking at a photo – anyone could determine which components had failed, making repair a doddle?

    Anyway – check whether the PCB input fuse has operated; it is the small black component on the separate PCB (use a multimeter to measure its continuity).

    If the fuse is OK, in my opinion the most likely component to have failed is the start up capacitor for the primary switching IC. The SMPS needs a voltage for this IC to initiate the HF switching (before the supply to the IC is generated from the transformer windings).
    When this capacitor fails – the primary switching IC cannot get started, so there is no output from the PSU.

    Looking at the photos, this capacitor is the one located just to the left of the transformer, smaller in size than the electrolytic reservoir capacitor (top left). Typically the start up IC capacitor is of the order of a few uF at around 50Vdc.

    As others have said you need to exercise extreme caution measuring mains voltages on such a PCB – but with mains power present you should have around 10-15Vdc across this component.

    If you have access to a capacitance meter, you could try measuring the component’s capacitance with it in circuit – which would give an indication if it is OK or not.
     
  6. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
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    im getting 156v on the 2 pins of the lg capacitor
     
  7. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
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    i would never buy a used printer unless it was a canon and dirt cheap. anyways this one is only about 1 1/2 yrs old and given me no problems aside from clogged print head one time which was fixed by soaking head on wet paper towel. im not really so much wanting to repair this as i just want to make sure its the problem before i purchase one. ebay i find used for 19.00 and new for a little under 30.00 i will buy it new.i just dont want to buy it and waste money if the motherboard or something else is bad. i paid 190.00 for this printer on amazon and have not used the 25 ink tanks that i purchased with it. i have meter out now and making tests. thank you for your input and i will let everyone know my findings
     
  8. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
    1
    actually its showing -156v with the meter set on 250v slot
     
  9. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    1,220
    156V, are you on 120V ac supply, can you take a picture of the 8pin chip (ic1) to see what number it is.
     
  10. Hymie

    Member

    Mar 30, 2018
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    What is the voltage across the small electrolytic adjacent to the large capacitor?

    I would expect to see 10-15Vdc (see my above post).
     
  11. dendad

    Well-Known Member

    Feb 20, 2016
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    One thing I have seen quite a few times on some power supplies is that they have a fairly high value resistor from the +HV supply to the controller supply. This starts the supply up, and after it is running, and AUX winding on the transformer supplies the +12 or +15 volts to keep it going. This resistor can go high and so not let the supply start.
    The symptom is the device runs ok but will not start up.
    If this applies here or not I don't know. But it may be worth tracing the circuit out.
     
  12. ebp

    Well-Known Member

    Feb 8, 2018
    1,595
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    You didn't say whether you had actually checked the DC output(s) of the power supply. With no load, the voltage you see on the big input filter cap is within the expected range with 110 to 120 VAC input.

    Check for voltage on the two electrolytic capacitors at the right hand edge of the board in your second photo.

    What is marked on the board next to the two tallish black rectangular objects that are more or less between the two caps mentioned above and the blue capacitor that is across the crosshatched bar printed on the board? (The crosshatched bar represents the barrier between input and output - to the left there be dragons (everything to the left should, for safety purposes, be considered to be connected directly to the AC line "hot")

    Is the printer turned on just with a power switch for the AC input or is there some sort of small push-button on/off switch on a control panel?
     
  13. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
    1
    no it does not power up or show any indication of getting power to the printer. before i even opened the psu i tested for power on the pins coming out when i touched one of them with my probe it sparked pretty good and was not due to me touching anything together. i made some tests for continuity on various parts on the board. and the are 3 resisters in a group. they dont have the color stripes used to display the properties of it. the 2 next to each other did not have continuity but the one below them did so i have to assume that i have to broken circuits on the board plus the one i damaged. im adding a pic and i circled and marked which one had continuity and the 2 that didnt. if everyone thinks that would be the cause for my printer not powering up and that the psu is in fact my problem then i will purchase a new one as soon as i see the post for about $27.00 on ebay and also work on maybe repaing the old one for 1.00 or 2.00 and having a bkup if this one fails. thank you everyone for your time helping me i think i covered everything in this msg. HYMIE i will get that done and put up the picture tomorow even though i think i have found the fault. board2.jpg
     
  14. dendad

    Well-Known Member

    Feb 20, 2016
    1,897
    481
    Just a thought, did you use the diode function when testing the diodes, and try both ways?
     
  15. led_lights

    Thread Starter New Member

    Jan 18, 2018
    26
    1
    no i used the continuity setting i.e. the triangle with the line at the end if my memory of what the symbols represent is correct. it is a really cheap digital meter bought from harbor frieght that i only trust its accuracy enough to have the general voltage correct and to basiclly tell me if something has any current at all and wether it it has continuity. if i tested 2 of these diodes and got no sign of a complete circuit in them but a sure complete circuit in the third one i tested. i threw the book to this away with out ever opening it as i purchased this for a big 2 story house i lived in that i was changing all of the electric outlets out and there was 3 sepperate breaker boxes involved so anything short of flippling the main off would be of any help without a test light or cheap meter. anyways, the diode test function is the 2 "T" shaped symbols that are turned sideways? correct? what sort of reading should i exspect from this? hi or low numbers, ect... i would like to be able to get to the bottom of wether my psu is at fault so i can get the new one ordered or purchase a new printer or a used one of the same model so that i would have parts to make possible repairs. that would be the only way i would buy i used printer. this one cost 200.00 a little under 2 years ago so i would expect a used one in good working condition may be worth something around 50 to 75 with shipping. sound about right?
     
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