Dodgy 7D PC connector, or dumb user?

Very much hoping the answer is dumb user...

I have a 7D. No problems using the built-in flash or a flash on the hot shoe. However, I can't get anything out of the PC connector. The camera was bought new, and has never previously had anything connected to it (i.e. I know the only dumb idiot that's used it is me).

I'd assumed the PC connector would be a simple ground+signal connector, where the two would form a circuit when you fire off a shot. I've used a multimeter (set to emit an audible signal when the two probes are connected) and unsurprisingly, if you fire a shot with one lead connected to the 'U' of the metal hot shoe and the other on the hot shoe's central 'sync' pin, the meter emits a short 'beep'.

Doing the same with the PC connector (one probe on the central pin, one on the metal surround) I get nothing. Nada. Zilch. I've looked through the manual, and gone through a number of on camera settings (manual flash etc.) and can't get anything out of it.

Is there some setting to enable the connection, or does it work differently and I've just misunderstood?

It's just a wag but maybe contact isn't good enough with the center pin of the PC. Maybe a call to Canon support would help.

Do you use liveview for this test? Don't! Because LiveView + Silent mode disables the PC-sync.

Thanks for the replies. I've been away for a while, but started to look into this again. A chat with Canon has resulted in the conclusion that the PC connector may be faulty, so it'll be going off to a local service centre in the next few days. Cross fingers it's a simple fix.

Got this sorted a while ago, but never got round to updating the thread.

Turns out the problem was an intermittently dodgy PC connector on the flash I'd borrowed. A little soldering of a dry joint and everything now works fine.

What confused the issue is that you won't get a signal (from the point of view of using a multimeter on the camera) on a PC socket. It needs to see a voltage from an attached flash in order for it to trip and fire the flash. On a hot shoe, you can check for continuity - but no signal on a PC connector doesn't mean it's faulty. Live and learn I guess.

sploo wrote in post #14624632
Got this sorted a while ago, but never got round to updating the thread.

Turns out the problem was an intermittently dodgy PC connector on the flash I'd borrowed. A little soldering of a dry joint and everything now works fine.

What confused the issue is that you won't get a signal (from the point of view of using a multimeter on the camera) on a PC socket. It needs to see a voltage from an attached flash in order for it to trip and fire the flash. On a hot shoe, you can check for continuity - but no signal on a PC connector doesn't mean it's faulty. Live and learn I guess.

The flash is just looking for a switch to complete the sync circuit. The camera supplies that switch. With the connection to that switch being either the hotshoe contacts or the PC port contacts.

But, the PC port acts just like the center and side rail contacts on the hotshoe.

Regarding:

"On a hot shoe, you can check for continuity - but no signal on a PC connector doesn't mean it's faulty. Live and learn I guess."

The opportunity to check the hothsoe or the PC port is identical. Note that on most (possibly all) Canon DSLR cameras that have both a hotshoe and a PC sync port, these are two distinct circuits. The positive contact (center port on hothsoe and center pin on the PC port) are not common.

There are a few posts in this forum regarding the reality that the hotshoe contacts and the PC port contact are distinct circuits (functionally two distinct switches). In many cameras this is not the case, the hotshoe contacts and the PC contacts use the same switch.

Enjoy! Lon

FlashZebra wrote in post #14625055
The flash is just looking for a switch to complete the sync circuit. The camera supplies that switch. With the connection to that switch being either the hotshoe contacts or the PC port contacts.

But, the PC port acts just like the center and side rail contacts on the hotshoe.

Regarding:

"On a hot shoe, you can check for continuity - but no signal on a PC connector doesn't mean it's faulty. Live and learn I guess."

The opportunity to check the hothsoe or the PC port is identical. Note that on most (possibly all) Canon DSLR cameras that have both a hotshoe and a PC sync port, these are two distinct circuits. The positive contact (center port on hothsoe and center pin on the PC port) are not common.

There are a few posts in this forum regarding the reality that the hotshoe contacts and the PC port contact are distinct circuits (functionally two distinct switches). In many cameras this is not the case, the hotshoe contacts and the PC contacts use the same switch.

Enjoy! Lon

Speaking with some electronic engineering colleagues; they'd explained that some circuits need to 'see' a voltage in order to fire (almost like releasing a piece of rubber that's being pulled - no tension, no firing).

If you have access to other DSLR bodies (especially Canon) I'd be interested in the results of testing continuity to see if the results are the same:

In short, connect the leads of a multimeter (that will sound a buzzer for continuity) to the ground and centre pin of the hotshoe respectively and fire a shot. The meter should sound.

Connect the same meter to the ground and centre pin of the PC port and fire a shot. The meter doesn't sound. I have even used a PC cable with a jack plug on the other end + croc clips to ensure there's a good electrical connection. Use that same PC cable with a flash or Cactus V5 trigger and the unit will be fired.

At least, that's the results I'm getting on my 7D. Hence a faulty flash causing the confusion that it might have been the PC socket at fault; due to no reaction from it (the PC socket) when used with a multimeter.

The switch in the camera is shorting a Voltage. This Voltage is produced by the sync circuit in the flash.

This is nothing special. A wall light switch does exactly the same thing.

Enjoy! Lon

FlashZebra wrote in post #14631925
The switch in the camera is shorting a Voltage. This Voltage is produced by the sync circuit in the flash.

This is nothing special. A wall light switch does exactly the same thing.

Enjoy! Lon

Yes, I understand that. You can short the pins on a flash (either hotshoe or PC connector) and get it to fire; it's just that the camera's hotshoe appears to be a much more simple trigger circuit (shorting regardless of whether anything's connected), but the PC connector appears to need to see the voltage supplied by the flash before triggering.

It's not a big deal - I only posted a follow up to close the issue, and to hopefully avoid anyone else falling into the same trap of assuming that no apparent triggering on the PC socket means the PC socket might be faulty.

FlashZebra wrote in post #14625055
...The opportunity to check the hothsoe or the PC port is identical. ...

This video should hopefully demonstrate my point about continuity testing on a hotshoe vs. a PC sync socket: http://www.youtube.com …rEnbcqOY&featur​e=youtu.be [Apologies for the Darth Vader sound effects; I was leaning over the camera that was doing the recording]

The 7D was set to manual focus, with a 2 second delay. To the left of the 7D is a short PC sync cable with a male jack plug (with the other end obviously connected to the PC socket on the 7D).

Down the bottom left of the video is a Cactus V5, set to transmit. The Cactus can be triggered by placing it on the camera hotshoe, or via a PC cable. In either event, it'll also fire its own hotshoe to trigger a flash.

At 0:14, the camera takes an exposure, and you can hear the multimeter indicate a short between the hotshoe ground and sync pin.

At 0:31, the camera takes another exposure, but there's no short between the ground and sync on the PC cable. Presumably because the multimeter isn't providing a voltage on which to trigger.

After plugging the PC cable into the Cactus, you can hear (at 0:50) that the hotshoe on the Cactus does short the ground and sync (confirming the PC socket is working).

Not shown in the video: as expected, the Cactus does provide a small voltage on the PC sync cable (just as a flash would).