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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 04 May 2014 (Sunday) 10:47
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Flash intermittently does not fire

 
CanonVsNikon
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May 04, 2014 10:47 |  #1
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Ok, I have Nikon gear but for this issue I don't believe brand matters as it is pretty universal.

I have a Nikon D700 and SB-800 flash. I know the flash is faulty but not sure if it is just flashtube or bigger issue such as main computer board on flash.

These issues occur whether in manual or TTL modes and on or off hotshoe.

So sometimes it will fire fine at correct exposure, than wait a few seconds and fire off another shot and it will either not fire at all or fire very underexposed (2-3 stops under). Funny thing is sometimes the flash will indicate that is underexposed and other times it won't indicate that anything is wrong even though shot was 2-3 stops underexposed.

Take another shot and maybe it will be correct exposure again or it may be 2-3 stop underexposed.

In manual mode at say 1/8th power same deal. Fires ok, underexposes, etc.

I have a few other flashes and they work perfectly every time.

This is not a battery issue or shooting too quick in succession.

A flashtube repair is not too expensive ($80) but anything else and it starts climbing.

Do you think the it is just the flashtube?

Thanks




  
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Wilt
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May 06, 2014 00:27 |  #2

It sure sounds like the issue is firing it again too soon sometimes!

Think of a bucket of water...


  1. if you 'mostly drain it', you have to wait for the hose to fill it before you can 'mostly drain it' a second time
  2. if you 'drain it a little', you can immediately 'draing it a little' and even be able to do that several times, before you have to wait for the hose to fill it -- before you can even 'drain it a little'.


Flashes fired at full power can need 15-20 seconds before the capacitor can be fully charged again (if not using an external battery pack).
READ your user manual for times you should expect to wait for a recycle to be complete!

CanonvsNikon wrote:
So sometimes it will fire fine at correct exposure, than wait a few seconds and fire off another shot and it will either not fire at all or fire very underexposed (2-3 stops under).

When you fire it the second time, it may be waiting to be fully recharged or it could have a very small remaining charge -- which is why it results in an underexposed shot!


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FlashZebra
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May 06, 2014 00:36 |  #3

Regarding:

"Do you think the it is just the flashtube?"

No, I do not think it is the flashtube.

Enjoy! Lon


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Whortleberry
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May 06, 2014 02:18 |  #4

FlashZebra wrote in post #16885071 (external link)
Regarding:
"Do you think the it is just the flashtube?"
No, I do not think it is the flashtube.
Enjoy! Lon

I'd modify that statement very slightly to say "No, I do not think it is JUST the flashtube". The tube itself may be a consideration, may be, but I'd suspect something a little more fundamental.

If you send a flash back to one of the mainstream makers (Nikon, Canon, Metz), they tend to simply replace the whole innards. Then you get back what is essentially a new flashgun in a secondhand case. Why do this? Simply, it's more cost efficient than tracking down intermittent electronic faults. However, the cost can equal or exceed the cost of a new flash. A couple of years ago, I had a Metz 54 MZ4i "mended" (GBP£115) and a friend in Ireland has just had a Nikon SB900 "fixed" (EUR150€) - in both cases, they simply replaced the innards. So you're probably looking at US$200 plus.

If you are sure (bearing in mind Wilt's analogy - one which I used to use myself back when I was teaching) that it's not a battery issue or sheer impatience, I'm afraid that it's going to cost you more than $80 to get it fixed. Better to bite the bullet and simply replace.


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CanonVsNikon
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May 06, 2014 09:23 |  #5
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I am 100% positive it is not the battery or sheer impatience. Fully charged batteries tested on two other working flashes and work 100% fine. Use those same batteries on this flash and works intermittently. And I am waiting for flash to recharge. Even at manual at 1/32 power waiting 5 seconds or more it still behaves the same way.

But I appreciate the responses. May be a bigger issue than just flashtube

Add to that, many times the first flash is the one that underexposes




  
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Wilt
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May 06, 2014 10:10 |  #6

It could be a failing thyristor. Thyristors are often confused by many flash users as devices used to MEASURE light output by the flash...they are actually 'switches' (not 'photosensors'). Thyristors act exclusively as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased (that is, while the voltage across the device is not reversed). Thyristors can control a relatively large amount of power and voltage with a small device. So something could be falsely triggering the switching action of the thyristor, or the thyristor itself could be flakey in its actions, thereby wrongly switching off the flow of current to the flashtube.


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CanonVsNikon
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May 06, 2014 10:35 |  #7
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Never heard of thyristors. Are they easy to swap out?




  
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Wilt
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May 06, 2014 12:19 |  #8

CanonVsNikon wrote in post #16885862 (external link)
Never heard of thyristors. Are they easy to swap out?

Thyristor is a single small component, relatively easy to change on the circuit board -- assuming the circuit is a multilayer board (a third layer or more of circuitry) and assuming you can figure out the right part (electrical characteristics). But as I stated, it could be circuitry Iexternal to the thyristor) which tells the thyristor to shut off electrical current flow, not necessarily the thyristor being flawed itself. To troubleshoot any circuit you need the schematics in order to figure out what should normally be happening.


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Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
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John ­ from ­ PA
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May 06, 2014 12:50 |  #9

This site has instructions on how to replace the flash tube on a SB-600 (http://www.dpreview.co​m/forums/thread/280604​2 (external link)) which may be similar. Read down a bit and some phone numbers etc. to get parts are shown.




  
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CanonVsNikon
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May 06, 2014 14:21 |  #10
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Thanks. Just sold it AS-IS for $80. More headache than it was worth




  
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Flash intermittently does not fire
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