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FLASH SYNC CONUNDRUM

David Lyga

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Location
Philadelphia
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I have a Pentax K1000 (Hong Kong) which has a problem with flash sync. First, as most of you know, this camera has an X-sync available for both PC cord and hot shoe at shutter speeds 1/60 and longer.

When I insert a charged flash (either PC or hot shoe) the flash immediately fires. If this were the only problem, case would be solved with this explanation: The sync prongs must be constantly touching and do not have to wait for the shutter to fire before becoming engaged.

However, the exacerbating problem is this: If left intact with the flash still connected and turned on, the flash re-charges and flash will fire at the normal 1/60 shutter speed, not before.

Of course, I would like to know how to rectify this, but there is one question that is even more compelling for me to query: How can a flash sync be shorted and then NOT shorted? Why is the flash able to re-charge when it is connected to the camera when it had immediately shorted. In other words, why is it not dissipating its charge constantly as it is still connected to the PC or hot shoe? Since it shorted immediately, without the shutter having been fired, then why is it not still shorting as it is still connected to the camera? This question could apply to most any camera.

I have both the top and bottom covers off but I cannot find the two metal prongs which are responsible for the sync connection which engages as the shutter is being fired.

NOTE: It does not matter whether the shutter is cocked or not. - David Lyga
 
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Hi David. This problem seems truly perplexing. Have you verified that your such cable is competent and without intermittent short circuit within the cable or connector? That happened to me once and I kept thinking it was a shutter problem when it wasn’t. Good to see you back after a bit of an absence!
 
If I've read this and understood it correctly David, I can't see anything wrong...?

You say that if you attach a CHARGED flash to the camera hot-shoe or sync socket, the flash fires?

BUT, if you then turn the flash off and attach it and then charge it, it fires with the shutter. Is this what you are implying?

If so I am going to have to double check my cameras and flashes, for as far as I can remember, but it has been a while since using an external flash unit, I think that mine do the same...?

Terry S
UK
 

It happens with either hot shoe or PC. Actually, it seems impossible that this could happen; maybe I am having a dream.
 

No, it might be a bit confusing. Follow closely: flash turned ON and indicator light lights. THEN, I connect flash to camera. It immediately fires. I KEEP it connected to camera with it still 'on'. The indicator light lights. Then I fire the shutter and perfect flash.
 
I expect it is something like the following:
In both cases, the structure of the mount - one a PC connection, the other a hot shoe - is causing a momentary short during the actual physical process of attaching the cord or flash.
It is a temporary, physical malformation issue, because when the cord is fully connected, or the flash shoe is fully in position, the contacts return to their correct position, and everything works properly.
Someone may have in the past tried to adjust things on the camera to make the flash connection tighter.
Have you tried different flash cords and different hot shoe flashes?
 
Oh and David - I'm glad to see you posting.
 
Hi @David Lyga, it's nice to see you post here, welcome back!

As to the charged flash firing as it's connected to the PC sync or hot shoe: my hypothesis is that the sync contact constitutes a small capacitance. When the terminals contact, this capacitance is charged by the voltage across the sync contacts on the flash unit; the corresponding voltage drop on the flash unit may just be enough to trigger it. If this is the case, it's really a borderline case.

Just to get this clear: the only problem is that a pre-charged flash unit fires immediately as it's connected to the camera, but otherwise the combination functions as expected? If so, how problematic is this situation? Personally, I'd accept it as a given, but perhaps I'm overlooking part of the problem.
 
I always avoided connecting a studio flash to a shutter while charged. Unless the pc connection was attached carefully somehow it would short and set off the flash. It wasn't a problem with the old bi-post connector, further apart?
 
Your "Shorting" of the flash does not "Short" the xenon tube. The xenon tube is ALWAYS SHORTED, or always connected directly to the capacitor.

"Shorting" the flash contacts causes a capacitive discharge which, applied to the spark coil, produces a high voltage which excites the xenon tube.

The K1000 is well documented and a good camera on which to learn. On the camera end of things the FP contacts are to be open to keep the flash from firing when attached. The FP contacts are not connected to a jack, but they are in the circuit on the K1000. They close when the mirror goes up and should open when the mirror comes back down. Rollei copied this system in the SL35.
 
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Speaking of collapse, I'm done in! I'm going back to magnesium powder
 
Hi David, it's good to see you around.
 
OK and with a bit of well-earned embarrassment I think that I "solved" my problem. The sync wires on the bottom of the camera were severed (but still partially connected) from a previous splice. This episode thus emanated wholly from an unsound electric connection. I fixed this and now all is well.

No matter how much experience one has with photographic hardware one can oftentimes still be relegated unto the realm of wanton stupidity. Please accept my shame and thank you all for your thoughts. - David Lyga
 
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