Troubleshooting Voigtlander 200 BC flash

[iamthejeff]

This little flash seems to be discharging itself whenever it charges to full capacity, or slightly before. I hear the capacitor whine as it's charging up but then it clicks and discharges itself. The odd thing is that the bulb is not flashing, it's coming from inside the flash unit. I took the cover off to see what was going on, and the flash is coming from this smaller cylinder stuck to the bottom of the capacitor. It sort of glows a little bit like a vacuum tube, and then lets off a flash of its own. Then the capacitor starts to charge again and the cycle repeats itself forever.

What is that, and what's wrong? Is it toast?

 

[AgX]

That part is a 2-electrode arrestor.

It is a gas-filled element (which explains the glow) used to lead off high voltages.
One typical use is the protection of devices from high voltage, as from a certain level on it becomes conductive out of itself (ionisation of the encapsuled gas) and can lead the dangerous voltage off to earth.

In your case it is used to quench the main capacitator once sufficiently long the flash tube has lit for correct exposure. Such elements were used in early or later plain autoexposure flashes, that controlled the discharge of the main capacitator, but the same time lost the residual charge.
The element in this application is a fast high-current opening switch shortcutting the main capacitator. In contrast to the more modern thyristor, which is a closing switch, thus breaking the current out of the main capacitator, and by that keeping the residual charge.

In your case the element got a copper bandage by which it is triggered, similar to the main tube. Basically that flash of yours has got two gas filled tubes switched in parallel to each other to the main capacitator. One tube designed for light emission and triggered to start illumination, the second designed for voltage discharge and triggered at the end of illumination.

Either that element becomes prematurely conductive out of itself when the main capacitor is still charging up, or its trigger-circuit is activating it prematurely in this phase.

 

[M Carter]

That's interesting - so it basically converts the un-needed current to light as a way to dump it?

 

[AgX]

No, the light is a side effect, in contrast to the main tube. It is just to shortcut the main capacitator.

But to follow your idea: one could instead install a second main tube, covered. BUT it would take longer to quench, and in any case it would heat up the whole device significantly. So, light output is not really wanted for that secondary tube.

 

[iamthejeff]

Thank you for the very detailed answer. So it's probably not repairable or at the very least, not worth it?

 

[M Carter]

No, the light is a side effect, in contrast to the main tube. It is just to shortcut the main capacitator.

But to follow your idea: one could instead install a second main tube, covered. BUT it would take longer to quench, and in any case it would heat up the whole device significantly. So, light output is not really wanted for that secondary tube.

Got it. I remembered in my musician days, a company made "blow-proof" PA speakers. They had a standard household light bulb in them, and if the wattage coming in exceeded a certain level, the bulb would get the extra energy - the idea was it would convert it to light, and the sound guy could see the glow and turn things down a bit. No idea how well it worked - doesn't seem to have become a standard though.

 

[AgX]

Not household but low-voltage, typically automiove. The wattage of the the bulb was to be as the max power of the speaker.

 

[marlio]

Hi guys,
I had this flash that came together with a camera. I didn't work and before dumping it I decide to open it and check if something loose inside. Then a found a cable broken but not sure where to sold it back.

The cable comes from the bottom of the lamp but not sure if it has to be attached to the on/off switch or to the capacitor(?)
I have marked both on the picture attached.
I looks to me that should be attached to the capacitor(?) but I am not sure.
thanks in advance for your help.