SF 20 Flash circuit diagram ... anyone?

[mikenic]

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My SF 20 flash doesn't. Ready light comes on, but won't trigger from test button or camera hot shoe contact. It is not a battery problem, probably trigger circuit I think.

 

Anyway, if someone has the SF 20 circuit diagram and is willing to share, it would be extremely helpful.

 

btw Thanks in advance for any heads-up on the dangers involved in this type of repair, but I am aware of the safety precautions needed wrt to the (lethal) high voltages inside the unit.

 

Regards all

[marknorton]

Sorry, I don't have a circuilt diagram, but you'll do well even to get the thing apart without breaking the plastic latches! If you do, do show us some pictures!

 

As you point out, the voltage on the flash capacitor can be retained for days or weeks and can give you a nasty jolt. I rememember when I took a Digilux 2 apart, the flash capacitor gave me a big spark when I discharged it, a sort of inanimate protest to my intrusion.

 

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First step of course would be to measure the voltage across the capacitor when the ready light is on.

[mikenic]

Thanks Mark, useful info.

Regards

[marknorton]

The capacitor acts as an energy store, able to deliver much higher levels of instantaneous energy into the flash tube compared to a battery.

 

If this capacitor was charged to 330v, it would hold 0.5 * 180 * 330* 330 micro Joules of energy or about 10 Joules. Discharge that into a flash tube over 1/1000 second and you have the lighting equivalent of about 10 kW or 160 typical domestic light bulbs, ignoring losses.

 

These so-called "flash capacitors" are designed to be able to withstand the thernal stresses of this type of operation.

[mikenic]

Thanks Mark

I think the problem is probably in the trigger circuit that ionises the flash tube prior to the main discharge. Areas I will be looking at first are the trigger TX (open circuit primary or secondary), the trigger capacitor and the trigger SCR (if used). The storage capacitor low volts can also give problems, but the "charged" light which usually senses this voltage is coming on saying all is well. We will see. Could also be the flash tube, but statistically rare.

As always, the actual circuit would be a huge help.

Regards

Mike