Canon T90 issue........not the usual one though !

Discussion in '35mm Cameras and Accessories' started by Firestarter, Sep 14, 2018 at 2:38 PM.

  1. Firestarter

    Firestarter Member

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    Some weird stuff happening with a Canon T90 I recently picked up. I was aware of the shutter issues these cameras suffer but wanted to purchase one anyway.

    The shutter is working perfectly, in fact most things are apart from two things.

    1, The DX codes always read at a quarter of film ASA so for example 100ASA loads as 25 ASA, 200 ASA loads as 50 ASA ?

    2, A weird problem. At times when pressing the metering mode button to change for example from average to spot the camera forwards the film as if you have just loaded it ?

    Anyone have issues like this before with a T90 or have any idea what the hell this mad electronic box is thinking ?
     
  2. OP
    OP
    Firestarter

    Firestarter Member

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    Think I may be getting somewhere with the meter button. it doesn't seem to be the meter button causing the problem after all. It seems that putting any kind of pressure or twisting motion on the camera top plate in the vicinity of the meter button makes the camera think I have just loaded a film. So looks like it may be a switch or similar for the film door that is causing the problem...must look further !
     
  3. abruzzi

    abruzzi Member

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    Have you tried other speeds?

    I looked at the actual codes (speed is just the first line): https://en.wikipedia.org/wiki/DX_encoding

    100 is: XOXOX
    25 is: XXXOX

    200 is OOXOX
    50 is: OXXOX

    The difference in both cases is the second block. So it could be one of the pins is sending the wrong signal.

    EDIT: if you put 400 speed film in block two should be black OOXXO. Since the second block is black, if it reads as 400, then its most likely a bad connection for that pin. If its still reads two stops low, then ? maybe exposure compensation?
     
  4. OP
    OP
    Firestarter

    Firestarter Member

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    Thanks, that could well be the problem, I will try a HP5 cartridge to see.
     
  5. OP
    OP
    Firestarter

    Firestarter Member

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    So I put in a 400 ASA and the camera displays..............400 ASA. Thank you abruzzi :smile:

    I will get a cleaning pen tomorrow for the DX pins and see if that sorts the problem.
     
  6. shutterfinger

    shutterfinger Subscriber

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    Ink eraser, pencil eraser both work for cleaning contacts as does metal polish.
    Likely insulation between the plate and body may have broken down or has been damaged from excessive, repeated pressure in the area.
     
  7. OP
    OP
    Firestarter

    Firestarter Member

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    Thanks, I will try an eraser and see if it helps.

    The camera looks like it has spent most of its life in its box so yes permanent pressure from the polystyrene packaging could have caused the problem.
     
  8. AgX

    AgX Member

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    Not necessarily it is a dirty contact pin thing, but it may be an erractic wire connection as with your door switch.
    If am right those contact pins are gilded, so you better refrain from abrasive means when cleaning it.
     
  9. Poisson Du Jour

    Poisson Du Jour Member

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    An eraser is the least likely of any methods I would personally use to clean the contacts. Isopropyl alcohol and a bud wiped over all of the terminals is a much better and safer idea.

    I suspect your camera has been tampered with in some way for the metering selection button to cause a drive advance. There is no custom function on the T90 that can otherwise change functions like those on later pro-level EOS bodies.

    The age of the camera, 30+ years, would also be indicative of a full overhaul service. A lot of these cameras were serviced within the first decade for high battery drain and erratic display driver behaviour.
     
  10. shutterfinger

    shutterfinger Subscriber

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    An ink eraser is like a fine contact burnishing tool, equivalent to 2000 grit sand paper approximately; a pencil eraser is like 4000 grit sand paper.
    Brass contacts corrode and need burnishing at times. A light pressure with either eraser is all that is needed.
    Metal polish works best and is least abrasive. Toothpaste (no water) on a cotton swab may work also.
     
  11. OP
    OP
    Firestarter

    Firestarter Member

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    Have been looking at the DX pins. They are all the same apart from the bottom 2 on the smaller rack where the pins look hollowed out, is this normal ? I will put a pic here, maybe someone with a T90 could compare for me.

    P1090505.JPG
     
  12. cooltouch

    cooltouch Member

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    I'm inclined to agree with shutterfinger regarding your meter problem. There are several flex circuit boards in that camera. One of them might have become abraded enough in one spot where there is contact being made when there shouldn't be. The fact that you can get the camera to do this when you torque the top plate lends credence to this possibility.
     
  13. Trask

    Trask Subscriber

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    The two “hollowed out” pins on your camera are identical to the pins in my T90. While I haven’t used the camera recently, it has always worked properly in the past reading ISO. Though I often bulk load and set the ISO manually. But — I don’t honk those two pins are the source of your problem.
     
  14. OP
    OP
    Firestarter

    Firestarter Member

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    Had a chance to remove the top plate today for a closer look and I have found the problem. It was simply a dry solder joint on the corner of the flexible circuit that has the meter mode button. So when I was pressing that button or putting pressure on the top plate in that area it was breaking or causing a circuit fooling the camera into thinking a film had just been loaded. A quick tap of a soldering gun and it is perfect now.

    Thanks, at least I know that is not the issue. As above I now suspect a dry solder joint somewhere, I will delve deeper when I have the inclination. For now I'm not too concerned as I rarely rate my film at box speed anyway. Would like to get it sorted though so the camera is 100%.

    Thanks for the pointers everyone :smile:
     
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