Electronic Photo Flash Repair

[pigdog]

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

 

[Arfa Daily]

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