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Repairing an erratic Sigma EF500 DG ST
Posted By: weijen, 07-09-2014, 07:48 PM

My Sigma EF500 DG ST started misbehaving on the eve of my vacation, forcing me to leave it at home. I had to rely on my pop-up flash for fill daylight fill instead. Needless to say, I got many less than ideal photos.

Anyway, the flash charges up but only seem to fire at 50mm zoom. This is the hallmark of a broken wire in the zoom head and by forums go, it's very fixable.

1. The first thing to do is to remove the rubber covers at the sides. Just pry them open. They're attached with double-side tape

2. Next, remove the screws (red) and lift up the cover. The screws securing the back piece of the head (green arrows) need not be unscrewed. More on this in step 3.

3. Ok, here's what went wrong. See the white wire floating? That's the signal wire. It's supposed to be connected to the red relay. In my case, the wire happens to touch the relay contact at only 50mm. At this point, please be careful with the tilt click stop mechanism (circled in yellow). DO NOT move the zoom head's tilt position. The spring and stopper will fly out and they're quite a bitch to put back in place. In fact I spent more time to putting these bastards back in place than actually fixing the broken connection.

OPTIONAL - If you're like me and hate the locking-push-to-release tilt head, now is a good time to do some modifications. To do that, remove the remaining screws on th axis and remove the back panel of the zoom head (cyan-1). Next, remove the "push" button (cyan-2). Again, be careful. A small spring will come shooting at you. Remove the spring and reinstall the button. Now the tilt will not lock at 0 and 90 degrees.

4. Here's a closer view of the broken connection

5. Here's the wire resoldered. It works like normal after the repair.

1. The symptoms of a broken wire in the flash head are:
- Flash turns on, charges and zoom but refuse to fire. Instead, you only get the sound of the relay clicking.
- Flash sometimes fire, but is erratic.

2. In my case, I did not have to discharge the capacitor. The components in the flash head are fairly isolated from the high voltage of the capacitor. As long as you know what you're doing and keep your hands off the metal parts, it should be fine. Still, it's a good idea to discharge the capacitor.
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07-11-2014, 10:46 AM   #2
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Thanks for sharing this!
I have the 530 model with erratic firing. It will be worth checking for this.

07-12-2014, 02:06 AM   #3
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That would be very much the case. Let us know if you can fix it the same way. As far as flash heads go, all brands and models are pretty similar.
07-13-2014, 05:19 PM   #4
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I just opened my unit hoping to find the loose wire, but everything looks solidly attached. Nothing was loose nor corroded.
But the symptoms are exactly the same. I tried at different zoom positions but did not notice any change. It fires about once in 10 or 15 tries.
I'll open it again to take another look.....


07-13-2014, 07:40 PM   #5
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That's too bad. You might want to take a look at the electronics at the lower body instead. The fault could be there. As long as it still fires, my guess it that it's a broken connection somewhere. If all fails, then put it on the bay "untested - as is - for parts or repair"
10-17-2017, 11:57 AM   #6
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Im new to this forum and your post looks interesting
I got a Sigma EF-500 DG Super from a friend
It doesnt fire but it turns on and all the features seems to work fine
How can i tell if its a burned tube or bad cap ?
04-03-2018, 06:21 AM   #7
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I have problem with wide panel , he fell out, I have no idea how it install back, has anyone tried fix this ?


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