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Vivitar 365 flash unit

Discussion in 'Electronic Repair' started by [email protected], Dec 11, 2012.

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  1. Guest

    I have an old 365 that I still use. Lately the capacitor has been getting hot. Cap is rated 1800uf 400V
    The flash works fine except for the heat.

    On checking I found that there is 465V on the cap. Even hooking it to a "dead" battery that only had 8V during charging, the cap still had 430V on it.I believe the cap is getting hot from the overvoltage. I've checked the cap on a Sencore Z meter, an ESR meter and with an ohm meter and all indicatethat it is ok. The Z meter showed a little dielctric absortion but not badfor a cap 30 yrs old and that size. Ohm meter tests in the 50meg I ran over all the diodes, resistors and semis that I could recognize. I found one semi in a TO-220 type package that reads 94 ohms between the outside leads.It reads .09 in both directions on a diode test. The tab-center lead readsaround 5meg to the other 2 leads and counts up like a capacitor charging. I have searched extensively on the net for info on this device and have found nothing. Anyone know what this is and if it's good or bad? My thoughts are that it is used to regulate the voltage applied to the cap and is not working. Any and all advice is apprecaited.
     
  2. N_Cook

    N_Cook Guest

    I have an old 365 that I still use. Lately the capacitor has been getting
    hot. Cap is rated 1800uf 400V
    The flash works fine except for the heat.

    On checking I found that there is 465V on the cap. Even hooking it to a
    "dead" battery that only had 8V during charging, the cap still had 430V on
    it. I believe the cap is getting hot from the overvoltage. I've checked the
    cap on a Sencore Z meter, an ESR meter and with an ohm meter and all
    indicate that it is ok. The Z meter showed a little dielctric absortion but
    not bad for a cap 30 yrs old and that size. Ohm meter tests in the 50meg I
    ran over all the diodes, resistors and semis that I could recognize. I found
    one semi in a TO-220 type package that reads 94 ohms between the outside
    leads. It reads .09 in both directions on a diode test. The tab-center lead
    reads around 5meg to the other 2 leads and counts up like a capacitor
    charging. I have searched extensively on the net for info on this device
    and have found nothing. Anyone know what this is and if it's good or bad? My
    thoughts are that it is used to regulate the voltage applied to the cap and
    is not working. Any and all advice is apprecaited.

    ++++


    What is the normal temperature for these caps , presumably when used near
    continuously.
    What does a thermometer tell you is the temp of you're one in use. As users
    don;t experience the heat of these caps , as they're enclosed, maybe its
    normal. As the volume of these caps is critical to the aesthetics/ergonomics
    I would not be surprised if they used underated caps, as the way they are
    used is different to the usual specified application.
     
  3. There's no question the capacitor is being overcharged. This is almost
    certainly due to failure of the "monitor" circuit that shuts off charging at
    a particular voltage. This guarantees consistent light output in /manual/
    exposure.

    You're headed in the right direction, but you're probably going to need a
    schematic to track down which component or components are defective.

    I had this problem with several Polaroid 360 cameras -- but the charging
    circuit had a pot you could adjust. You might look for one.
     
  4. wrote: > I have an old 365 that I still use. Lately
    the capacitor has been getting hot. Cap is rated 1800uf 400V > The flash
    works fine except for the heat. > > On checking I found that there is 465V
    on the cap. Even hooking it to a "dead" battery that only had 8V during
    charging, the cap still had 430V on it. I believe the cap is getting hot
    from the overvoltage. I've checked the cap on a Sencore Z meter, an ESR
    meter and with an ohm meter and all indicate that it is ok. The Z meter
    showed a little dielctric absortion but not bad for a cap 30 yrs old and
    that size. Ohm meter tests in the 50meg I ran over all the diodes,
    resistors and semis that I could recognize. I found one semi in a TO-220
    type package that reads 94 ohms between the outside leads. It reads .09 in
    both directions on a diode test. The tab-center lead reads around 5meg to
    the other 2 leads and counts up like a capacitor charging. I have
    searched extensively on the net for info on this device and have found
    nothing. Anyone know what this is and if it's good or bad? My thoughts are
    that it is used to regulate the voltage applied to the cap and is not
    working. Any and all advice is apprecaited.

    the to-220 is probably a SCR for the quench circuit, if this flash has
    one.

    it would be connected to a inductor.
     
  5. Bruce Hawkes

    Bruce Hawkes Guest


    The handle of the flash unit where the cap is housed gets so hot you can't hang on to it. That's what prompted me to take it apart.

    I have put the cap back on the Z meter and one an intensive leakage test onit. The meter has 396V across the cap (measured with an external DVM) and is only showing 440 microamps of current through the cap and it's cool after 15-20 minutes of this voltage applied. No signs of heating at all. It appears the cap survived being over heated/charged drastically. I have no idea how they monitor/regulate the voltage. The circuitry is pretty simple with no processors or logic involved that I have found. I'm beginning to doubt if the 3JM device is involved in that control, but I still don't know.
     
  6. Bruce Hawkes

    Bruce Hawkes Guest

    There is a pot on the one circuit board. It is not labeled. I turned it 1/8turn, fired the flash and let it recharge and the voltage was the same. Iwill do some more checking in that area to see if I can find anything. I wasn't sure what the pot would be for. It would stand to reason that it would be a voltage control, but it didn't see to do much when I turned it.
     
  7. There is a pot on the one circuit board. It is not labeled. I turned it
    It might be calibration for the auto flash. Can't hurt to experiment.
     
  8. Did you measure the voltages on either side of the TO220 device? I'm
    thinking that if it were some type of regulator , (with an "in" or
    "out") then you might get a clue from seeing what that looks like.
    Maybe the pot controls gate current. Lenny
     
  9. I checked a manual for a 365. it is a "thyristor" model.

    Any beefy device on the HV side will be a SCR as I said earlier, and in
    series with an inductor. The voltage across it will match that of the
    storage cap.
     
  10. I checked a manual for a 365. it is a "thyristor" model.

    TO-220 device is almost certainly the thyristor. It sits between the storage
    capacitor and the flash tube. It's normally "on". When the auto-exposure
    circuit determines that correct exposure has been obtained, the thyristor is
    shut off, killing the flash tube's output.
     
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