Newbie Question - Diode Identification

Discussion in 'The Projects Forum' started by NickK, May 3, 2010.

  1. NickK

    Thread Starter New Member

    May 3, 2010
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    I'm working on upgrading a Canon CR4 retinal camera that uses a Polaroid camera to a digital camera. It's a pretty bold project for me since I have very little electronics experience, but it seemed pretty straight forward, so I went for it. Everything was going as planned until I screwed up something on this board. Diode D306 in the attached picture measures a forward voltage drop of .002v, while the other 5 diodes measure just under .600v. Also, D306 has continuity. This board controls the existing Polaroid camera, which is no longer being recognized. So, I'm guessing the problem is at the very least the D306 diode. I tried to find a replacement but I haven't had any luck.

    Thanks for taking the time to read this and any input would be greatly appreciated.

    [​IMG]
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Chances are pretty good that a common 1N4148 would do for a replacement. The diode D306 is bad.
     
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  3. mik3

    Senior Member

    Feb 4, 2008
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    The problem is probably the diode, however, other components might case the diode to appear as shorted. Maybe a soldering splash or a bend pin.

    You can read the part number on the diode and google it to find which diode is it. If you can't post what is written on the diode here.
     
  4. NickK

    Thread Starter New Member

    May 3, 2010
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    I can't thank you enough for your help. I'll let you know how it works out.
     
  5. NickK

    Thread Starter New Member

    May 3, 2010
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    I replaced the diode and that wasn't the problem. The new diode gave the same reading. But, I did find out that when I disconnect the white wire from position 1 the diode tests at just under .600v. The white wire leads to a small motor that lifts a mirror up so that a picture can be taken. I also found that resistors 302, 304,305 & 306 tested at 13.4k. I'm slightly colorblind but they appear to be red red orange gold which is 22k +/- 5%. The other 2 resistors tested within range.

    Should my next step be to replace the resistors?

    Thanks and any help would be greatly appreciated.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    That may be the old problem of checking components in circuit. If there are any other paths, then a resistor will check lower than the stated value. Diodes, especially across motors as suppressors, will always looks bad.

    Time for the obvious question - what isn't working? Is that darlington driver (the TD62004) in working order? http://www.alldatasheet.com/view.jsp?Searchword=TD62004
     
  7. NickK

    Thread Starter New Member

    May 3, 2010
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    I'm really in over my head but I'll do my best. This circuit board (which operates the polaroid camera) has a round 9 pin male connector that connects to the main body of the retinal camera. The retinal camera doesn't detect it. It's like it's unplugged. Also, prior to whatever it is I did, some of the colored wires would read 3v and 6v. Now I get nothing.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Without a schematic, this can be interesting. You can always try the shotgun approach, and replace components, hoping to find the bad one. That would suggest the TD62004 next.

    Those critters are not to be found, though. The acceptable drop-in substitute is a ULN2004, which may be had from Jameco - http://www.jameco.com/webapp/wcs/st...amecoall&ddkey=http:StoreCatalogDrillDownView

    It might be interesting to have some idea of what happened. Did any wiring get disturbed, did the batteries survive unharmed?
     
  9. NickK

    Thread Starter New Member

    May 3, 2010
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    The way it happened was strange. The project seamed simple enough. All I had to do was identify which of the wires signaled the polaroid to take a pictures and which ones signaled the internal camera flash. I had figured out the polaroid part and ran a connection to a digital camera. It worked perfectly at least a dozen times. I then started to try to figure out the flash when I accidently touched to wires together. It was a good thing actually because it just so happend to trigger the flash. I touched them together a few more times and worked great. I thought I was home free. I then turned off the power and connected the flash wires to a flash sync on the digital camera. When I turned the system back on nothing worked. I can't remember exactly but I may have tried it one time with everything hooked up and then it failed. Maybe the digital camera sent a current and damaged something? I think I'll just buy a bunch of parts and have at it.

    Thanks for the tip on the TD62004 substitute, that would have taken me a long time to figure out. I'll start there and see what happens. Thanks again for all your help.
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    For future projects, I would avoid the 'crossing of the wires' approach.

    You may have been discharging the cap into a different path to the flash.

    It may have been a couple hundred volts. The short duration may have lasted for a few go's, but eventually something went to component heaven.
     
  11. BMorse

    Senior Member

    Sep 26, 2009
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    Does the camera you connected it to still work? If those were the high voltage wires you connected it to, you could have damaged more than the controller.... Post some pics of both parts, as large and clear as you can would be great, both sides of the circuit board would be good also...


    B. Morse
     
  12. NickK

    Thread Starter New Member

    May 3, 2010
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    The camera still works. Here's a picture of the whole project.

    [​IMG]
     
  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Wires 1 and 2/3/11/12 are across the diode. If those are connected to a coil or transformer or motor, that would explain the "short" in circuit test. If it's a transistor, that transistor could be shorted.

    You can lift them one at a time to see which one causes the short and then work to the other end of the wire to see what's going on. There must be a component connected to the wires in number 1 and the other's.

    Good luck.
     
  14. NickK

    Thread Starter New Member

    May 3, 2010
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    The white #1 wire does lead to a motor and when I disconnect it, the D306 diode then tests at just .6v, just like the others. Could the motor be the problem?
     
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I see from your second photograph that not all the wires are connected.

    Do you have a schematic? If not you should trace the board and draw the schematic.

    How did this board become part of your project?

    I doubt the motor is the problem. You can measure the resistance of the motor and see what the coil resistance is.
     
    Last edited: May 4, 2010
  16. NickK

    Thread Starter New Member

    May 3, 2010
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    I don't have a schematic. I replaced the TD6200 and it didn't help. The R304 resistor tested at 13K but when I removed it, it tested at 22K, which is what it's supposed to be. The 302,305 & 306 also test at 13K. I haven't tried removing them yet. I'm hoping this provides some type of clue. Thanks again for all the help. - Nick
     
  17. NickK

    Thread Starter New Member

    May 3, 2010
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    Also, when I test the resistor in the board it display 22K for a split sec. before dropping to 13K.

    The board is part of the original system that controlled the Polaroid.
     
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    What is the model number of the Polaroid?
    Have you tried to get the technical documentation?

    I don't like the fact there are too many wires disconnected so there is no way to verify if they are properly connected.

    Attached is what I can make out from the pictures ... and since you have access to an ohmmeter, you can verify and correct the drawing.

    It seems the number 1 wire(s) supply the +V to the circuit.

    The diodes may not be 1N914s, but they are small signal diodes.
     
  19. NickK

    Thread Starter New Member

    May 3, 2010
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    I can't thank you enough Joe. I really appreciate it. I followed your link to fcctests. Are you in Lainsburg? The reason I ask is because I'm in Toledo, OH and travel through Lansing a couple times a month. I would much rather hire a professional, like yourself, to work on this. I could drop off the whole unit to you. Let me know if you're interested. -Nick
     
  20. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Nick,

    I'm only in Laingsburg till May 12th, then I will be in Grand Prairie TX.

    What is the model number of that unit, as maybe you can get the technical documentation and work through it to get it up to snuff.
     
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