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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Electronic Photo Flash Repair
Hello all.
I am repairing a Nikon SB-80DX flash and I do not have the benefit of a schematic so I was hoping someone could share their thoughts on my findings. I think I have narrowed the problem down to a faulty transistor. Please see http://www.dondoucette.com/sb80dx.jpg for an illustrative picture. When I fire the flash I get a voltage pulse at location 1 in the photo pulse is of correct amplitude and duration. Location 2 at the transistor is connected to the one side of the capacitor shown, the voltage here is 285Vdc. Location 3 at the other side of the capacitor is connected to the purple wire that is connected in the flash head to the primary side of the trigger coil. Am I correct in assuming the pulse at location 1 of the transistor should be amplified and show up at location 2 allowing 285Vdc to briefly pass through the capacitor to the purple wire located at position 3 which in turn will be stepped up by the trigger transformer and trigger the flash? When fire the flash I do not get any voltage at the primary of the trigger coil but I do get a pulse at location 1 in the photo. I am not looking for a definitive answer of any kind just an opinion on the validity of my findings. Sincerely, Donald W. Doucette |
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"pigdog" wrote in message ... Hello all. I am repairing a Nikon SB-80DX flash and I do not have the benefit of a schematic so I was hoping someone could share their thoughts on my findings. I think I have narrowed the problem down to a faulty transistor. Please see http://www.dondoucette.com/sb80dx.jpg for an illustrative picture. When I fire the flash I get a voltage pulse at location 1 in the photo pulse is of correct amplitude and duration. Location 2 at the transistor is connected to the one side of the capacitor shown, the voltage here is 285Vdc. Location 3 at the other side of the capacitor is connected to the purple wire that is connected in the flash head to the primary side of the trigger coil. Am I correct in assuming the pulse at location 1 of the transistor should be amplified and show up at location 2 allowing 285Vdc to briefly pass through the capacitor to the purple wire located at position 3 which in turn will be stepped up by the trigger transformer and trigger the flash? When fire the flash I do not get any voltage at the primary of the trigger coil but I do get a pulse at location 1 in the photo. I am not looking for a definitive answer of any kind just an opinion on the validity of my findings. Sincerely, Donald W. Doucette Your analysis of the circuit operation sounds about right. The only thing that I would say is that the switching device is often a thyristor, rather than a transistor. Have you checked to see what the device is ? It could make a significant difference as to whether the drive waveform at point 1 is correct or not. Arfa |
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