Olympus A-11 flash, no ready light

[Kirks518]

I picked up an XA with flash at my local thrift store a couple of weeks ago, and the flash doesn't want to work.

I can hear it charging up loud and clear, but the ready light never comes on, and nothing happens when I hit the test button or fire it through the camera, even after waiting an absurdly long time.

Could this be due to a dead flash tube, or would it be something else? I have a parts A-11 available, but have never worked on flashed, so I'm not sure where to begin. If it is the tube, is it replaceable?

 

[shutterfinger]

I suspect the charge circuit is at fault. A capacitor is charged to provide the voltage necessary to fire the tube, the ready light should come on once that charge has been reached. The flash will not fire unless the trigger voltage has been reached. The flash tube should have 3 contacts, cathode-connects to the battery/circuit negative/signal return, anode-connects to the output of the charge circuit, trigger- momentarily connects to charge circuit output when the test button or camera flash sync completes the circuit. The main capacitor can hold a charge high enough to put your heart into fibrillation even if the flash has been off for an hour or two. It should be discharged through a 10K ohm resistor before working on the circuit. I do not what voltages should be present but a search for flash tube voltage shows xenon tubes to be around 340V.
http://www.bristolwatch.com/ele/

 

[AgX]

Could this be due to a dead flash tube, or would it be something else? I have a parts A-11 available, but have never worked on flashed, so I'm not sure where to begin. If it is the tube, is it replaceable?

In this respect the tube has nothing to do with the charging circuit and thus with the neon indicator bulb.

The tube is a kind of open switch. A switch however that due toits design cannot inadvertently close during charging.

 

[DWThomas]

If the unit has been unused for a long time, as in years, the capacitor may have degraded to the point where its leakage prevents it from reaching a fully charged state. It is claimed that sometimes "reforming" can improve the capacitor but I have no first hand experience with doing that. One supposedly keeps applying a charging voltage over a period of time to restore the degraded internal dielectric layer. The old and unused flashes I've encountered (including one of my own!) were beyond that stage, the charging circuit oscillator would not start to even try to charge.

So assuming it has been unused for a long time and the oscillator does still start, I suppose you have little to lose by running it for a while over a day or two and see if it behaves any better. It's also possible the indicator is kaput (in which case the unit might still fire), but I suspect that's not likely.

The explanation upthread is approximately correct, but the primary charge of the capacitor is across the ends of the flash tube at a voltage insufficient to break down the xenon. The trigger electrode in the center of the tube is zapped by a much higher, but low current spike from a pulsed transformer or inductor. That starts the ionization of the gas whence the capacitor discharges through the tube (all in less than a millisecond!) And yes, you do not want to get any parts of yourself across that capacitor!

 

[John Koehrer]

You would be surprised how fast your reflexes are and how far you can throw a screwdriver over your shoulder
when you hit a charged cap. Doesn't do the screwdriver blade much good either.

If the other A11 has the same symptoms I wouldn't bother swapping parts but if different you might just swap out the circuit board.
It should have eveyrthing on it except the flash tube and main cap.

Stay aware of shutterfingers tip about discharging the cap.

 

[Kirks518]

I think 'reforming' the capacitor is as far as I'll go with it. The other A-11 has corroded battery contacts, and who knows what else. They're cheap enough where I'll just get another one if this one won't reform.

 

[shutterfinger]

The reforming of a capacitor that I'm familiar with is to momentarily apply a voltage that is higher than the capacitor's rated voltage. The higher voltage can sometimes burn the weak spot in the plates of the capacitor so that they are no longer shorted. The reforming voltage should be 10V to 25V higher than the capacitor's rated voltage and not be applied for more than 1 or 2 seconds. I have never done this. Another way is to disconnect one lead, power up the circuit then momentarily connect the lead with a jumper. The rapid charge will sometimes burn the leak spot in the capacitor's plates so that they no longer make contact. Either of these methods work a small percentage of the time where the capacitor holds 80% or more of its charge. I have connected capacitors in series with a variable DC power supply and an amp meter and found the voltage at which the capacitor started leaking. Another way to check leakage is to disconnect one lead and use a jumper wire to connect that lead to the circuit, power the circuit with the jumper in place, disconnect the jumper, turn the circuit off, then check the capacitor voltage 20 to 30 seconds later, the longer the capacitor holds the circuit's working voltage the better the capacitor is. A volt meter's internal resistance will discharge the capacitor so be quick in reading the voltage. All this only works with electrolytic capacitors. Circuits are designed so that the components can take a momentary surge if the equipment malfunctions.

 

[AgX]

A volt meter's internal resistance will discharge the capacitor so be quick in reading the voltage.

Digital voltmeters are prone to that. They even may trickle the release circuit. Better use a coil-meter.