Vivitar 3500 "zoom thyristor" flash won't whine

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

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...).

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

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?

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

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

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.

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,