Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old September 13th 20, 11:01 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

I have three of these flashes that I've converted to manual flashes. One
works ok, The second i have to turn on and off several times, but it
finally starts whining, and works perfectly thereafter so long as it stays
on.

The third used to do that too, but now it won't whine at all. I've taken
it apart, and the main capacitor checks out good, as does the main power
switch. So I'm left with tryng to figure out why the boost circuit doesn't
start up - doesn't oscillate. The smaller electolytics look ok, but I
haven't taken them out to check them. And of course there's no schematic.

I'd like to find a fix, but I don't want to make a second career out of it
either. Any suggestions on what to check, or how to approach this?

Thanks very much.



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Old September 15th 20, 08:38 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

On Monday, 14 September 2020 01:22:16 UTC+1, Ralph Mowery wrote:
In article ,
says...

I have three of these flashes that I've converted to manual flashes. One
works ok, The second i have to turn on and off several times, but it
finally starts whining, and works perfectly thereafter so long as it stays
on.

The third used to do that too, but now it won't whine at all. I've taken
it apart, and the main capacitor checks out good, as does the main power
switch. So I'm left with tryng to figure out why the boost circuit doesn't
start up - doesn't oscillate. The smaller electolytics look ok, but I
haven't taken them out to check them. And of course there's no schematic.

I'd like to find a fix, but I don't want to make a second career out of it
either. Any suggestions on what to check, or how to approach this?



If there are any small electrolytic capacitors I would chanage them.
Many switching supplies have the problem where the capacitors go bad.
One way that may help confirm that is to take the one that sometimes
works and heat the capacitors with a hot air gun or even a hair dryer
and then try starting it. If it starts up faster the capacitors are a
sure bet.


Another other way to test them is to piggyback a new one on, see if it springs to life. Another way is to use a component tester.


NT
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Old September 15th 20, 10:08 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

On Sunday, September 13, 2020 at 2:01:59 PM UTC-7, Peabody wrote:
I have three of these flashes that I've converted to manual flashes. One
works ok, The second i have to turn on and off several times, but it
finally starts whining, and works perfectly thereafter so long as it stays
on.

The third used to do that too, but now it won't whine at all. I've taken
it apart, and the main capacitor checks out good, as does the main power
switch.


As others have mentioned, that usually is an oscillator-startup problem, and
the entire circuit is ONE feedback loop oscillator; every component is a suspect.
With age, high voltage parts are most susceptible to failure; the HV rectifier
and its associated switch (SCR or transistor) that drive the coil are inexpensive
to replace (except you'll have to identify them, and match to modern available
parts, and pay shipping for onesies...).
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Old September 16th 20, 12:23 AM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

On 9/15/20 1:38 PM, wrote:
Another other way to test them is to piggyback a new one on, see if it springs to life. Another way is to use a component tester.


NT


That ONLY works if they're open.
You should know that.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com


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Old September 18th 20, 01:44 AM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

On Tuesday, 15 September 2020 23:23:23 UTC+1, Fox's Mercantile wrote:
On 9/15/20 1:38 PM, tabbypurr wrote:


Another other way to test them is to piggyback a new one on, see if it springs to life. Another way is to use a component tester.


NT


That ONLY works if they're open.
You should know that.


I don't know that. Both methods work if they're low C, high ESR or open. A component tester also works if they're leaky or shorted.


NT
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Old September 20th 20, 10:54 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

I have three of these flashes that I've converted to
manual flashes. One works ok, The second i have to
turn on and off several times, but it finally starts
whining, and works perfectly thereafter so long as it
stays on.


The third used to do that too, but now it won't whine
at all. I've taken it apart, and the main capacitor
checks out good, as does the main power switch.


As others have mentioned, that usually is an
oscillator-startup problem, and the entire circuit is
ONE feedback loop oscillator; every component is a
suspect.


With age, high voltage parts are most susceptible to
failure; the HV rectifier and its associated switch (SCR
or transistor) that drive the coil are inexpensive
to replace (except you'll have to identify them, and
match to modern available parts, and pay shipping for
onesies...).


I removed all of the electrolytics, and all but one tested
good on my scope. I replaced the dubious one, but the flash
still doesn't work. The oscillator whine doesn't start up.

But I did find one thing that gets really hot when the power
switch is turned on. It is a pair of three-pin parts
(triange pattern footprint) that look like cylinders, and
they are enclsed in a U-shaped heatsink. They are each
marked with the Mitsubishi triagle logo, and "B324ST", with
"12" on the second line. I assume they are transistors or
thyristors, but searching for them comes up with nothing.
This is all from the 1980s, so I guess it's not surprising
that the parts aren't active anymore, but it would be nice
to at least find a datasheet.

By the way, the dubious cap was right next to the mystery
pair.

Any ideas?

https://www.eevblog.com/forum/repair...0-speedlight/?
action=dlattach;attach=1070818;image

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Old September 20th 20, 11:06 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

Someone on the EEVblog forum says the part number is actually 2SB324, which
is a germanium PNP transistor. I'd guess I won't find a direct replacement
for that.

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Old September 21st 20, 01:18 PM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

On Sunday, 20 September 2020 at 17:06:12 UTC-4, Peabody wrote:
Someone on the EEVblog forum says the part number is actually 2SB324, which
is a germanium PNP transistor. I'd guess I won't find a direct replacement
for that.

If you need 2SB324 transistors, I have them in stock. They don't have the heatsink attached, but I have heat sinks as well.
Send me a private message so we can connect.

Dan
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Old October 12th 20, 06:28 AM posted to sci.electronics.repair
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Default Vivitar 3500 "zoom thyristor" flash won't whine

Peabody wrote:
Someone on the EEVblog forum says the part number is actually 2SB324, which
is a germanium PNP transistor. I'd guess I won't find a direct replacement
for that.


NTE still sells crosses for stuff like that. Looks like NTE102A. Must be
old stock. I doubt the chinese would even fake those.


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