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. |
Vivitar 3500 "zoom thyristor" flash won't whine
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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...). |
Vivitar 3500 "zoom thyristor" flash won't whine
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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 |
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 |
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. |
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 |
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. |
Vivitar 3500 "zoom thyristor" flash won't whine
On Monday, 12 October 2020 00:28:53 UTC-4, Cydrome Leader wrote:
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. OP may provide details, but I supplied transistors to him and as of this writing, one is working by changing transistor and some caps. Dan |
Vivitar 3500 "zoom thyristor" flash won't whine
abrsvc says...
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. OP may provide details, but I supplied transistors to him and as of this writing, one is working by changing transistor and some caps. Yes, thanks very much, Dan. I found that one of the two ganged transistors had failed short. So I replaced that one with one of Dan's 2SB324 transistors, and I replaced the two electrolytic capacitors, one of which tested bad for ESR. And now it works. I have two more of these flashes which still work, but don't always spin up when I first turn on power. I'm going to make sure their transistors are good, but I'm going to replace their capacitors. The existing ones are 35 years old, so it's not too soon to replace them. They are Panasonic CE series, which don't appear to have been anything special. Thanks for bailing me out, Dan. I was thinking of trying to switch over to silicon transistors, but at least for now I don't have to do that. These flashes run on two NiMH AAs, so about 2.4V, so the lower base drop of germanium may actually be important. Anyway, I was not looking forward to making that transition. |
Vivitar 3500 "zoom thyristor" flash won't whine
I have two more of these flashes which still work, but
don't always spin up when I first turn on power. I'm going to make sure their transistors are good, but I'm going to replace their capacitors. The existing ones are 35 years old, so it's not too soon to replace them. They are Panasonic CE series, which don't appear to have been anything special. I did the capacitor replacements, and now all three flashes seem to be working nominally. The high-ESR capacitor on the first flash also measured bad on the other two. But the replacements tested fine. I guess the old ones could have been bad from the beginning, but other CE series caps of that vintage don't have high ESR. So maybe the way they are used in the circuit tends to kill them. They are just 10uF, 16V. Nothing special. |
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