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 Post subject: strange strobe light issue...
PostPosted: Fri Sep 08, 2017 6:03 pm 
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Location: USA / North Carolina / Fayetteville
i have a powerful Whelen Strobe light 3 outlets alternating flash...
i have a lot of experience with these power supplies.
the unit will charge up, and fire 1x, and then the arc is maintained in the tube.. it will not extinguish to recharge and flash again,
and you can still hear the trigger ticking.. my 1st instinct is that the storage caps are weak or bad.. so i clipped a big cap onto the supply leads, it still does the same thing.. what gives ? what can be causing the are to not go out..
the arc is not bright at all, it is like plasma in the tube.. but it is enough current that the tube gets hot..
on the dual circuit that can flash 2 tubes at once, if i have 2 tubes on,, the unit might flash properly for maybe 2 or 3 seconds, but then does the same thing..
i'm baffled
i have not called Whelen yet. trying to see if i can figure it out 1st..


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 Post subject: Re: strange strobe light issue...
PostPosted: Sat Sep 09, 2017 5:27 am 
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This is a common issue with older photographic strobes. Xeon tubes have a firing voltage and a much lower extingishing voltage.
The tube does not extinguish because the power supply voltage on the capacitors did not drop low enough on the last firing of the strobe to extinguish the arc. The firing must drop the voltage low enough on the firing pulse or the tube will 'hang fire'. The power supply, trying to charge the capacitors is powering the residual arc in the tube.

Older storage capacitors are usually the cause because they don't supply enough energy to fully fire the tube hard enough to discharge themselves. Probably the tube firing sounds soft instead of a sharp pop. A parallel capacitor is not a proper test since if the capacitors are leaking, the same problem low energy situation exists. Change them with known good ones to see if that solves the problrm. Occasionlly the tube is at fault since reduced gas pressure will reduce the tubes operating parameters, and the lowered arc current has a similar effect.



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 Post subject: Re: strange strobe light issue...
PostPosted: Sat Sep 09, 2017 4:33 pm 
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Thanks, the strobes do pop hard when they do fire, the test tubes i am using are not tge same ones
That are on the vehicle, so it is not a tube issue. I thought the caps might be a issue, i have so e here i can sub out. But they will not fit in the unit. But they should be ok for testing purposes.
I just never heard that weak caps can cause a sustained arc. But then again i guess it is basically the same as trying to work it without a cap at all.


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 Post subject: Re: strange strobe light issue...
PostPosted: Mon Sep 11, 2017 10:35 am 
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interestingly enough i called Whelen today and the tech i talked to said that some of their strobes have a de-ionization circuit. so he says this may have gone bad.
he said if i get him the model number etc, that i can get a schematic. so when i get home i'll call em..
i never heard of a de-ionization circuit before..


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 Post subject: Re: strange strobe light issue...
PostPosted: Mon Sep 11, 2017 11:31 am 
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Location: Maryland
Oh..k. I never heard of that, so please post an update.



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 Post subject: Re: strange strobe light issue...
PostPosted: Tue Sep 12, 2017 11:12 am 

Joined: Mon Dec 06, 2004 1:01 am
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Location: Tennessee
You have my attention also.. I've worked on a few, none successfully though !


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 Post subject: Re: strange strobe light issue...
PostPosted: Tue Sep 12, 2017 1:12 pm 
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Some photographic strobes have an 'optical feedback' design that uses a thyristor, or small gas tube like a neon, connected across the flash tube, triggered by a photocell, to quench the arc. This terminates the arc at some value, providing a more stable light output, or a shortened duration flash. It also extends the device's battery life by reducing the discharge on the storage capacitors so they do not have to go through a full charge cycle for each flash, but that seems like an entirely different issue.

There's a great deal of information on strobe technology here: http://repairfaq.cis.upenn.edu/sam/strbfil.htm



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 Post subject: Re: strange strobe light issue...
PostPosted: Sun Sep 17, 2017 10:24 am 
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i got a copy of the schematic for this strobe, but the tech would not really tell me where the de-ionisation circuit was.
so i am trying to guess at it..
i tried to attach the schematic but it is too large to post... it is a PDF file.. i cannot figure out how to post one page at a time..


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 Post subject: Re: strange strobe light issue...
PostPosted: Mon Sep 18, 2017 9:02 am 
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Can you use the Windows Screen Capture, or others, to take a snip of the drawing area around the strobe tube?



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 Post subject: Re: strange strobe light issue...
PostPosted: Tue Sep 19, 2017 6:15 am 
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Location: USA / North Carolina / Fayetteville
see if this works here....
the De-ionazionation circuit consist of
D18 & D19 and R28 , the tech finally told me...but he said that the Hybrid chip 66907 can also possibly get destroyed.
usually it is one of the diodes that gets shorted.


Attachments:
strobe schematic A.PNG
strobe schematic A.PNG [ 149.6 KiB | Viewed 740 times ]
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 Post subject: Re: strange strobe light issue...
PostPosted: Thu Sep 21, 2017 10:23 am 
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well i got the strobe checked out,, the diodes checked out ok, so the chip is bad.. and Whelen won't sell me a chip.. kinda sucks..
i used to be able to buy chips from them, but now they won't sell to me.. so i guess the unit is a parts unit..


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 Post subject: Re: strange strobe light issue...
PostPosted: Thu Sep 21, 2017 11:34 am 
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The 66907 number?

Is that all, or are there other characters?

A lot of manufacturers aren't making their own in house chips.
They are using off the shelf PROM's or PIC's that they can put their own firmware on.
Thus, making it impossible to replace a damaged one.
Unless you can find a working PROM or PIC that you burn a copy of. :(


Signed: Janitor Tzap


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 Post subject: Re: strange strobe light issue...
PostPosted: Fri Sep 22, 2017 10:28 am 
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ok,, possibly good news... i didn't quite give up yet,, i i searched and searched and called and called, i finally got a whole part number.
61-0566907-00 it is listed as a hybrid "Feed back HR " so it is some sort of feed back control device.
i got in touch with a company that happened to have about 50 on hand... i think they were hording them all..lol
anyway, they were $16.00 each.. so i got 2, just encase.
they should be here sometime next week... wish me luck..


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 Post subject: Re: strange strobe light issue...
PostPosted: Mon Sep 25, 2017 9:22 am 
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the diodes # D18 and D19 can they check good and actually be bad ? these are weird diodes, one is a avalanche diode, and the other is a Schottky diode.

i am going to order some just in case,, i can find the D18 Easily ( 1N5061 ) but the Schottky diode D19 (IR60S1) is a booger to find...i only can find 1 source in Germany on Ebay,,
anyone have some laying around ? or have a US sourced location ?


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 Post subject: Re: strange strobe light issue...
PostPosted: Mon Sep 25, 2017 10:30 am 
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Location: San Jose CA
good idea, you could have a good forward voltage but the reverse breakdown voltage could be dramatically changed. Unless you were using a sensitive curve tracer, it would be hard to judge leakage and forward resistance. Reverse breakdown voltage could be quite large for a strobe unit making it hard to measure without an older curve tracer like Tek 577 that can go to 3500V for that measurement.

Part numbers often go obsolete. Get the specs for that diode then do a parametric search on Digikey to find some cross references with similar values.


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