which is the positive?

Discussion in 'General Electronics Chat' started by nichos, Aug 29, 2012.

  1. nichos

    Thread Starter New Member

    Aug 29, 2012
    My old lazer printer gave up the goat.

    Opened it up & noticed one wire of a capacitor corroded & disconnected from it.

    Purchased from RS one similar in values & 3quarters shorter.

    From the attachments which is the positive hole on the PCB & is the longer wire of the capacitor positive?

    Please excuse my ignorance, ........nick
  2. Tealc


    Jun 30, 2011
    The long leg is the positive side. I can't make out much sense from the image and I'm not aware of the labelling convention as shown.
  3. Markd77

    Senior Member

    Sep 7, 2009
    There should be a vertical stripe on the side of the capacitors with minus symbols within it. Simply install the new one to match the old one.
    The symbol you have drawn (not one I was familiar with) is for a polarised capacitor, see this page:
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The negative side will probably be at ground. With power off, check both pads with an ohm meter to a known ground point on the board. That will reveal which pad is negative and which positive.
  5. nichos

    Thread Starter New Member

    Aug 29, 2012
    Thanx all,

    1. got the positive Long wire on capacitor.

    2. my meter shows :-

    a) Both show continuity to ground, the right hole more so, &

    b) there is continuity between the two holes.

    c) new attached foto showing in the middle clearly at C4 the holes with the white circle round the right hole, would that zig-zag indicate where the ground is?.

    Hope this does not mean the PCB is nagered??? !!
  6. SteveHow

    Active Member

    Jul 2, 2012
    What is it not doing, obviously not printing, but what are the symptoms. I had one where the Corona Wire had snapped. They are as thin as a strand of human hair. You can diagnose these issues by looking at the print. i.e is it all Black.

    And yes I did put a new Corona Wire in it....very hard to do, you need tweezers, Magnifying Glass and patience. :)

    It was a $10,000 laser printer in its time. (hard to believe I know)
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    To me it looks like the negative pin on the caps are marked with a circle on the PCB. Both the negative on C8, C17 seems to be connected to the same partial plane as C4. And it make sense that this is ground plane
  8. nichos

    Thread Starter New Member

    Aug 29, 2012
    Very observant "afre" Good point. Shal I try it though, & then I may.

    But how about the continuity I mentioned 3-4 post before? They seem to be both Earthed.

    I should have mentioned it at first. When I click to print it says printer is not connected.

    I changed the printer to PC USB cable & made sure both ends are connected proberly but no luck.
  9. Markd77

    Senior Member

    Sep 7, 2009
    It also looks like they are using a thick line on one side of the outline of the capacitors to denote negative, what a difference a clear photo makes.
    Measurements made in circuit take a bit of interpretation, for example the continuity measured between the pads of the removed capacitor is probably due to the other capacitor. When you test, current will flow through the capacitor, but if you leave the probes there for a while the capacitor will charge up and the apparent resistance will increase. There will be other components that will affect the readings in other ways.
  10. nichos

    Thread Starter New Member

    Aug 29, 2012
    Sorry just managed to take a decent shot.

    I soldered the Captr with the short end to that circle but still no print.

    It just stays there & when I open the printer icon it gives the document name & everything else but nothing in the "Status" that usually says printing.

    When I say "soldered the Captr" although it seems firm on the board, I have my doupts because in my ignorance trying to solder the legs, the negative hole lost its solder inside (as if is empty inside) & cannot possidively solder that wire & look the usual blob although is covered now, difficult to explain.

    I could not fill the hole with solder & push the wire through it.

    Also there must be an underlying fault that burned the captr that I can never detect.

    I gues it is the end of the line & be best to bin the damn thing. It is the Canon FAX-L360, god knows how old it is.

    Thanks for all your help .......nick