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09-11-2021, 01:28 PM   #16
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Thank you Bob for the comprehensive circuit analysis. Other than the higher voltage NE2X I had it pretty much figured out. I did learn that there are 110 V Zeners, too (I normally think of these for low voltage regulation)!

09-11-2021, 04:40 PM   #17
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QuoteOriginally posted by AstroDave Quote
Thank you Bob for the comprehensive circuit analysis. Other than the higher voltage NE2X I had it pretty much figured out. I did learn that there are 110 V Zeners, too (I normally think of these for low voltage regulation)!
Thought some here might find the explanation interesting. There are a lot of older flashes laying around which have nearly the same circuit. Note that the high voltage from the main capacitor should not be available at the flash trigger contacts (well, actually it is the same voltage value-wise, but it's across a 0.02 microfarad capacitor and not the main cap, the latter of which would pack a much larger wallop should one access that).

Zeners are available up into the 200 volt range and are made by connecting lower value Zener elements in series. In the case of this flash circuit, the Zener is used to drop the high voltage so it won't appear at the transistor circuit which disables the oscillator (which would destroy Q3, and possibly Q1, and Q2). This works as long as a small current is pulled through the Zener (always used in reverse breakdown mode, hence we're dealing with a negative voltage on the right side of D2 relative to its left side).
09-11-2021, 09:55 PM   #18
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A friend in high school felt that a pc connector was too loose on his old Honeywell Strobonar 770 so he bit it to squish it down. In a few minutes he was fine.
09-14-2021, 11:39 AM   #19
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LOL, I got dinged pretty good with my old Vivitar once while myself and some friends were drinking way too much Jameson, we rigged it up to see what would happen and believe me it woke me up pretty good! What we do while boozing with friends back in the late 1970's was fun but in today's world not so much!

09-14-2021, 03:37 PM   #20
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QuoteOriginally posted by Bob 256 Quote
Thought some here might find the explanation interesting. There are a lot of older flashes laying around which have nearly the same circuit. Note that the high voltage from the main capacitor should not be available at the flash trigger contacts (well, actually it is the same voltage value-wise, but it's across a 0.02 microfarad capacitor and not the main cap, the latter of which would pack a much larger wallop should one access that).
I know this is a little late to the party, but I actually have a copy of the schematic for the Viv 283 (very similar to the Viv 285) from the service manual of same. (Crummy quality, but the connections to the hot shoe are clear.)

Name:  viv_283_schematic.png
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...and the description of how the trigger circuit works...

Name:  viv_283_trigger_desc.png
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Size:  180.9 KB


Steve

Last edited by stevebrot; 09-14-2021 at 03:55 PM.
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