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Dual battery powered tube light - blown transistors

Discussion in 'Troubleshooting and Repair' started by Cirkit, Nov 6, 2021.

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  1. Cirkit


    Oct 28, 2015
    I have a battery powered dual tube light and one side fails with the transistors blowing.

    Attached is a photo of the PCB.

    The two D882 transistors on the left keep blowing. What would be causing this?

    Attached Files:

    • PCB.jpg
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    Last edited: Nov 6, 2021
  2. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir cirkit . . . . .

    You gonna have to give this 'ole dummy some degree of assist . . . . on that there . . . " battery powered dual tube light " daffynition.
    Can I assume that the lamps are quite hefty white LED units . . .OR . . .fluorescent*** tubes ? .
    *** Hinted at, by the presence of those 4 reddish brown .22ufd poly caps.
    I am seeing, on the right side . . to me . . . a quite fractured BLOWN apart transistor, its being the one with a black wire routed above it.
    I am seeing Power related circuitry at the top right corner with 4 HEAVY diodes and 4 more of the 1N4007 sizing.
    Also there is an AC input at the top, which I might assume for run power and/or charging, if not using battery power.
    The AC wires blue color coding suggests that its coming from the LV secondary of a line powered transformer.
    The bottom symmetrical power supplies suggest having two lamp banks being fed, with just one of them failing on you.
    Can you confirm that if you pull the set of transistors, of the bad portion, that the good lamp might still work with its good transformer power circuitry. IF the BAD section didn't take out a shared function. IF using LED lamps . . . .vice CFL***.
    How about the battery family / types, Amps and Voltages , and can I assume that they would normally be kept trickle charged by this unit.
    The relay is using a 9VDC coil, sort of suggestive of a 12 VDC power supply.

    Talk to me . . . .

    Your AVATAR . . . . . . I see you still got the old IBM SMS systems circuit cards . . .circa 60's . . . . that I once used.

    73's de Edd . . . . .

    WHY IS IT CALLED . . . . . " TOURIST SEASON " . . . . . IF'N WE CAN'T SHOOT 'EM?

    Last edited: Nov 6, 2021
  3. Cirkit


    Oct 28, 2015
    Thanks for your reply 73's de Edd.

    This is quite an old unit so they are indeed fluorescent tubes.

    You are right in that the blue wires are from a linear transformer which is to charge the battery and also run the tubes too.

    The two tubes can run independently or separately, selected by a switch.

    The battery is a sealed lead-acid 6V 4.5Ah type.

    The relay switches from mains power when the supply is removed to battery power.

    The circuits for both tubes appear to be identical and I measured the resistances of the coil windings previously with the damaged transistors removed. Both were the same.

    One tube still works with the other's circuitry damaged. I measured all the capacitors before replacing the transistors so am at a loss as to what might have caused them to blow again?

    The transistor with the black wire above it has some glue across it which makes it look like it's damaged, but it's fine. That together with the transistor to the right of the transformer below the inductor are the original ones.
  4. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Cirkit . . . . .
    You say . . . . .
    You are right in that the blue wires are from a linear transformer which is to charge the battery and also run the tubes too.

    I would now venture to say that the BLUE wire pair feed into the FWB made with the 4-1N4000 series sized diodes.
    This power quad feeds over to the far top left corners C1 E-cap and makes a lower power supply of 12VDC ? to accommodate the cluster of discrete components in that boards top left corner.
    Circuitry there also serves to detect AC power presence and auto engage the TIANBO power relay to go to battery powering in loss of AC line power.
    That area also provides low level constant trickle charging of your back up battery.

    The RED wire pair feed into the larger 1N5400 diode set is making a FWB that feeds the MAIN C10 E-cap at right mid side and this combo powers the units lamp driver solid state circuitry on normal AC line powered operation

    The two tubes can run independently or separately, selected by a switch.
    As in one tube working ,or the other tube working, or BOTH tubes working ?

    You say . . . . .
    One tube still works with the other's circuitry damaged

    Can you swap tubes to confirm that BOTH will work with that now functioning transformer.
    Lets talk fluorescent tubes now.
    What physical / dimensional configuration ? Are they being small CFL /fluorescent units or older style, long stick units with a dual pin contact on each extreme end?
    Also of what wattage ?
    Do I see the heavier white wires about the lamp driver transformers as being the interconnects to the tube ?.
    Trace out the wiring path from a transformer to its 4 ? tube connections and then back to its transformer for me.
    I will pre guesstimate . . . . . that one wire from a transformer goes to one end contact of a stick tube and its other side contact goes to a wire that will run down the length of the tube and connect to one pin contact at the other pair of contacts and then that last pin will run over to the transformer as its final connection.
    There you have a complete power wiring loop for one tube.
    With my digression of the EXACT involvement of the two orange .22 HV poly caps, other than DC isolating of the AC/pulsating DC feed from the transformer to the fluorescent tube. You can fill me in on that EXACT wiring aspect.

    You say . . . . .
    " transistor to the right of the transformer below the inductor are the original ones."

    Okey-dokey . . . .the transistor under the black wire has its brass heat sinking tab outward and exposed.
    The other transformers transistor set has its Q5, has its brass heat sinking tab outward ALSO, so outwards is norm . . . . therefore . . . you made no CBE terminal error in the install of the side by side pair of replaced transistors . . .right ?

    The two transformers / electronic ballasts are utilizing a transistor pair and a feedback winding to make two independent power oscillators to feed the two fluorescent tubes.

    I say . . . . .
    If this was being MY duck to pluck . . . . . .

    I would get the unit operational with that one tube working and lit up.
    Then put the switch to BOTH tubes working position.
    Now since you will need to pull those two bad transistors , do so now , and then you leave that circuit less its drive medium, so you then get two lengths of hook up wire so that you can run a wire from vacated collector connection of the naked unit over to the companion / respective collector of the WORKING unit and solder tack on connections.
    Repeat the procedure , with like connections for the other two collectors.
    You now want to see if powering up will have both tubes . . . .being possibly dimly or dimmer . . .lighting up.
    If that works, that clears the transformer of shorted secondary winding turns.
    And the only other things associated, are two or more resistors and two or so diodes in those POWER osc circuits other active discrete components.

    Added thought . . . . if no GLORY of a dual tube light up . . . .then reverse the transistor collector leads positions AT only one of the transformers, . . . . ? possible weird phasing aspects might also be involved ?

    Know WHUTS ? . . . its bein' . . . . . Go DOG GO . . . . . time . . . .

    ASIDE . . . . I want to associate the hefty 3 ohm fusible resistor at top center with the IN5400 higher power circuitry.

    You sort of bottom clipped the component side photo coverage.
    Can you provide a full closeup of the foil side pattern, well lit, no light reflections, being shot flat on, with no parallax..

    73's de Edd . . . . .

    I say . . . . .
    All syllogisms have three parts; therefore, this is not a syllogism.

    Last edited: Nov 7, 2021
    Cirkit likes this.
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