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Motorola Transistor Replacement

Discussion in 'General Electronics Discussion' started by Kepo, Jan 23, 2018.

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  1. Kepo

    Kepo

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    Jan 23, 2018
    FCAE01E0-C996-4219-8FD8-2DAE3C316EDF.jpeg I’m in need of help finding a replacement transistor for the one pictured. It is in a circuit that regulates voltage to approximately 13.5v dc from 28v dc. Any help is very much appreciated.
     
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Perhaps MJE802...??
     
  3. Kepo

    Kepo

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    Jan 23, 2018
    I don’t have enough experience in this field to say that it would work. I haven’t found a datasheet on the transistor I have yet.
     
  4. Bluejets

    Bluejets

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    Oct 5, 2014
    If you can find the circuit, perhaps someone will be able to help.
     
  5. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Such transistors may be Darlingtons as well as conventional so care must be taken to ensure you get the right replacement. The schematic would reveal the 'type' (Darlington or not) but such components are rated in single-digit amps and around 10-30W dissipation a la BD139/140.

    http://pdf1.alldatasheet.com/datasheet-pdf/view/4869/MOTOROLA/MJE802.html

    Indeed if it is an MJE802 (highly likely) it is a Darlington as per the datasheet above.
     
  6. Kepo

    Kepo

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    Jan 23, 2018
    F4322D75-1837-4561-A4B6-4DCF8A187A8F.jpeg R C1AD493B-0298-48BA-9A86-16B0562F4A3A.jpeg 93A8E0BB-2DB8-4477-87AC-5CDFA63FD242.jpeg I have been unable to find a schematic for this circuit but I do have these pictures if this would help.
     
  7. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Kepo . . . . .

    All of the clues are there . . . .
    FR varnished board circa . . . a . .la . . . . .1976-1977
    It is being a Motorola brand and they OWN that very specific casing profile

    MJE802 . . . . . NPN Motorola darlington

    Fill us in on what the numbers are on the two small signal plastic transistors.

    The wire bundling is covering up the marked PINK part . . .suspecting it to be another 1N400X family power diode or a low value resistor..
    If so, confirm silver polarity bands position.

    To start on analysis feed us the 12 DC voltages being read on the C,B and E's of the 4 transistors.
    The BLACK wire and the outermost encircling foil path is your ground referencing.

    Also take a reading ACROSS the WHITE marked diode that is probably being your ZENER reference diode for the regulator proper.

    I could not see the metal thermal side of the bottom 802, but expect the left terminal to be the Emitter and the far right being its Base . . .with the central C being a given.

    BOARD LAYOUT . . . .


    [​IMG]


    73's de Edd
     
    Last edited: Jan 23, 2018
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  8. Kepo

    Kepo

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    Jan 23, 2018
    Thanks for the help Edd. I should be able to get that info for you later this evening.
     
  9. 73's de Edd

    73's de Edd

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    Sir Kepo . . . . .

    Looks like I mispositioned a 2K resistor to the left side of the 1K resistor , with that paired cable also hiding another resistor that would then be to the left of the 2K resistor.

    Also what terminal or parts node does the end of the obscured YELLOW wire tie into, if not being at the tinned number 6 solder terminal as I have it shown ?

    Considering that the BLACK wire will be the common connection to the 28VDC input and the 13.5 VDC output.

    What do the YELLOW-BLUE-GREEN-RED wiring connections relate to connecting to externally . . .with high consideration of the RED being either 13.5VDC or 28VDC ?

    Also, of the two pot adjustments , is there a high probability of the 5K pot on the half of the board that the Zener is located on, being an output voltage adjustment.

    While that might leave the other 5K pot to adjust current output.

    One of your photos created a peep thru . . . . to be able to see that the lower 802's leads are being a reversed mirror image of the top one on its B and E connections.

    73's de Edd
    .....
     
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  10. Kepo

    Kepo

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    Jan 23, 2018
    Ill start by describing the application. This is an electric trim control for a older aircraft being restored. On power up 24vdc is supplied to the red wire #1 of the trim regulator witch then regulates output on the orange wire #3 to the switch at +/- 13.5vdc. The switch then controls the output of blue wire #5 and green wire #4 to the trim motor reversing its rotation and also to the circuit board which should control 24vdc clutch output on #6 yellow wire. The clutch output is energized anytime the trim motor runs forward or reverse. Trim motor speed is then adjusted using the two pots one for forward the other for reverse. I suspect the burnt JE802 transistor was overheated from a fault at the switch that has since been repaired. I am posting a schematic now with more info to come as soon as possible.

    KEPO
     
  11. Kepo

    Kepo

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    Jan 23, 2018
    E52C7D0B-2A2C-403F-8F4B-E11B1D5733A7.jpeg
     
  12. Kepo

    Kepo

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    Jan 23, 2018
    021DF965-713B-40FB-AD58-F3CBDF813881.jpeg C261A93C-C397-4947-BDD2-F91773B552A2.jpeg 6545282D-CB0A-4E51-9949-380DACCB8123.jpeg
     
  13. Kepo

    Kepo

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    Jan 23, 2018
    I hope to have time tomorrow to do some testing to get more info.
     
  14. Bluejets

    Bluejets

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    Oct 5, 2014
    Ah,ha......as I thought.
    Transistor with it's back to us (clutch driver) in the older pics is different type.

    Thought I'd spend an hour or 2 and see if I could trace the pcb into a readable schematic.
    Maybe Edd will comment further on any mistakes etc.

    Cheers ...Jorgo


    Aircraft2.jpg
     
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  15. Kepo

    Kepo

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    Jan 23, 2018
    Thanks Jorgo that will surely help.
     
  16. Bluejets

    Bluejets

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    Oct 5, 2014
    Aircraft3.jpg O.K..... revised with the numbers ...
    Cheers Jorgo
     
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  17. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Kepo . . . .et Jorgo . . . .

    Post 16 Looks fine to me . . . . if having no minor wire color coding, nor erroneous terminal connections

    If you have a TR4 POWER TRANSISTOR failure, it would relate to getting either no or excess voltage to the trim motor/actuator.

    If you have a TR2 POWER TRANSISTOR failure, it would relate to no capability of clutch action or a continual power application to the clutch, up to its . . . P O O O O O O O F . . . factor limitation.

    Do a touchee-feelee walk around of ye olde tymey Cess-ner Skyhawk . . .
    Do preflight check . . . . get airborne . . .set to directional bearing . . . get to preferred cruise altitude . . .set in the preliminary trim of throttle for cruise speed. . . . . trim time

    System Run though . . .

    24VDC power comes in from RED (1) wire . . .immediately encounters two directional / one way steering diodes which routes + DC power polarity to the right to the TR4 POWER TRANSISTOR or to the left to the TR2 POWER TRANSISTOR, used as the clutch driver.
    This transistor with a few ancillary parts reduces the initial 24VDC down to the lower voltage used by the trim motor.
    The Zener on the base of the TR3 is being the main regulation reference along with some corrective sampling being inserted via the two steering diodes associated with the center taps of the two 5 K 10 turn pots, they establish up and down trim tab limits.
    You then have reduced voltage coming off the emitter of TR4 POWER TRANSISTOR, then carried down the path of ORANGE wire to RED wire (2) and it is just waiting for disengage switch to be flipped to its engage position.
    Upon ENGAGE, DC power power immediately rushes to the trim motor and the two steering diodes across the motor immediately differentiate on the terminal with the positive voltage and it feeds to the 2 resistors voltage divider bridge that feed into the base of TR1 and its conduction and then placing full base drive to the TR2 POWER TRANSISTOR.
    The conducting TR2 routes 24 VDC thru the other steering diode to the clutch which has been in its dormant / power off condition and had been mechanically locking the trim tab into its last set position.
    NOW the trim motor is incrementally moving the trim tab either up or down, in accordance as to where the Up-Dn
    double pole double throw switch to the left was setting.
    Toggling between the switches finally gets you trimmed into leveled flight with the set elevator doing the heavy work and the trim tab just " fine tuning " in adjustment.

    A final disengage switch flip and the power drops from the clutch and it mechanically locks the trim tab, while that diode at the emitter of TR2 absorbs the inductive kickback from the clutches inductance.
    The trim motor is now being dormant also after power drop to it..

    You are all set up . . . . that is until . . .lil two ton Tessie, seated in the rear, swings her gluuuuut-a -mus MAAAAXIMUS, around in pivoting and turning to see if that dropped M&M can be retrieved from the seat fold.
    You just swing your body weight fully back to compensate for the slight dive that encroached. . . . then . . . . . . a final normalcy again.


    Thassssssit . . . .


    73's de Edd
    .....
     
    Last edited: Jan 27, 2018
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  18. Kepo

    Kepo

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    Jan 23, 2018
    I would like to say thanks to everyone who helped out with info on this pcb. After replacement of Tr4 (MJE802) all bench tests were good and upon installation in the aircraft all ground and flight tests where also good. So we won this battle.

    Thanks again

    Kepo


    By the way Edd, to not disturb the weight or balance of the aircraft we ALLWAYS keep two ton Tessie strapped in tight with the M&Ms out of reach.
     
  19. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Kepo . . . . .

    Forgot to ask later, after having initially noticed. But possibly you had to mechanically / physically tear down a bit to get down to the single naked board state.
    Perchance is there a rectangular, insulative mounting mica spacer on each transistor and an inner thick alum-i-ninny-yum-yum heatsink plate involved ? Or individual heatsinks. . . . . . . since I DO seem to see tin / or / beryllium oxide + silicon grease residue being visible upon the two transistors flush, heat sink tabs.

    Why did TR4 fail . . . . .?

    There is a VASTLY APPRECIABLE difference in a merely air cooled power transistors power handling capability / capacity, and it being mounted to a properly sized heat sink.

    Aside . . . .
    MAN! . . . . that's being one all laid back and CON-tented dawg in the Logo . . . . resplendently arm grasping its security "blankie" / pillow.

    73's de Edd
    .....
     
    Last edited: Feb 6, 2018
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  20. Kepo

    Kepo

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    Jan 23, 2018
    The transistors do have heat sinks however not enough to save TR4 when a overload occurred on the output to the trim motor. This problem should not reoccur.

    The dawg pictured is a vizsla belonging to my daughter seen here relaxing in HIS recliner.

    kepo
     
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