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Can't find datasheet or info on a transistor T477 185,552

Discussion in 'Datasheets, Manuals and Component Identification' started by Bastien01, Apr 17, 2016.

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  1. Bastien01


    Apr 17, 2016

    I'm currently studying the board of an old video enhancer of the 80s, it mostly uses 3904 and 3906 but one transistor is different, it has "T477 185,552" written on the package, but I didn't find anything about it on the internet.
    Does anyone have seen one before?


  2. Anon_LG


    Jun 24, 2014
    Nowhere that I can find on Google, if it's old and obscure, you may never be able to find a data sheet. What do you need it for? Is it broken? Can you test it? Is it definetly a transistor?
  3. Bastien01


    Apr 17, 2016
    I'm currently writing down the circuit in order to understand how the enhancer works, anyway everything seems to work fine. I don't know if it's a transistor, i said that because of the TO-92 package but it's true that it can be something else. I tried to test it onboard, with the diode test i got that (i numbered the pins like on a NPN):

    1 (+) 2(-): 0,8V
    1 (-) 2(+): 0,5V
    1 (+) 3 (-): OL
    1 (-) 3 (+): 0,8V
    2 (+) 3(-): OL
    2 (-) 3 (+): 0,8V

    I don't know if it's relevant since it's on board.

    I also mesured the voltage between the supposed emitter and collector when it's turned on and shorted base and emitter and no voltage surge, and when shorting base and collector with a 10K resistor, no voltage drop. I tried this test on other NPN/PNP on the board and it seems to work, so i don't think it's a NPN or PNP.
    It's difficult to test it on board, and desoldering it isn't an option since i don't know what it is, if i damage it, i'll be f****d.

    Thanks for your reply!
  4. 73's de Edd

    73's de Edd

    Aug 21, 2015
    SIr Bastien0 . . . . . . . .

    None of my shelves of ole design databooks of the 70's and 80's help me on that number .
    We can consider that is a small signal NPN and I CAN tell you that the EIA code of 185 tells us that was a MOTOROLA manufacture.
    The 552 is indicative of it being stamped as it was rolling off the production line as the 52nd week of 1985.
    AND it is a bit of a "pwemium bwewed " unit , what with those gold flashed leads.
    I can't see the unit being ultra critical of its Ft ( freq) spec in that units particular application.
    The one thing, that I really think, is that it might be a unit with a higher than normal beta (gain) .
    Can you beg-buy-borrow or steal a transistor tester to check that units DC gain . . . . .some El cheapo MULTI function DVMs even offer that capability.

    OR a few resistors and a meter and a 9 Voltses battery, will let you breadboard one up . . . with use of a bit of internet tutelage.

    73's de Edd
    Last edited by a moderator: Apr 28, 2016
  5. Bastien01


    Apr 17, 2016
    wow thanks a lot for these infos! The DVM that i have can do hFE but i don't have the optional adapter required to use it, i'll check if i can find a transistor tester or i'll build a circuit as you suggested. To test, i'll need to desolder it, I really fear to damage it, any advices other than not heating to much?

    Thanks again for your reply!
  6. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Bastien01. . . . . . .

    I'm currently studying the board of an old video enhancer of the 80s.

    With that meaning that you are going to use it to enhance the high end slope of a video waveform for less degradation in its being copyied over to a second tape . . . . .or that you are using it to be a way
    around "Stop Copy" or "Macrovision" in the duplicating of a commercial Movie / tape.

    The DVM that I have can do hFE but I don't have the optional adapter required to use it.
    I will be telling you of a safe pull so that you can plug in the transistor . . . . but here is how I would make my own adapter.

    My . . . My . . . .My . . . . now, this is where your real "Canadian ingenuity" comes into play, you should find that a 1/4 watt carbon resistors lead should be a snug fit into that meters transistor socket.

    Cut three 1/2 inch lengths of that size of wire and make center L bends , then get three lengths of lighter gauge hook up wire and solder tack them to the L wires ends. Then the neatest thing to use is 3 of these.
    Hook clips that connect to the loose wire ends and then the test clips clip onto the transistor being tested.
    The hook clips are cheapest from Radio Shack, if Canada has, or ever had such.


    You could color code each with paint or label with stick on tape .

    That adapter should then hold a solid electrical connection to let you test a transistor.

    If you like it and want to make a socket, use some of the 2 part clay consistency epoxy that you finger knead to mix and warm up.
    Tear off a mixed piece that is then formed into a cylindrical "bullet" that is a bit larger in diameter that the 3 wires spacing to each other.
    Straighten the L bends out, so as to then be raising straight up from the socket connection .
    NOW you have to move pretty fast to . . . . .
    Feed the bullet down to within an 1/8 of an inch of touching the transistor socket, compress the wires inward to embed within the epoxy a bit then add a bit more of epoxy around the outside, if the wires didn't embed well..
    Unplug from your socket and square off the bottom of the blob, smooth the sides and plug back into the socket to hold pin alignment and let it cure overnight.

    You should now have a test adapter for the future.

    To test, i'll need to desolder it, I really fear to damage it, any advices other than not heating to much?

    75 years of progressively refined and enhanced experience . . . is now coming forth:

    Use an acid brush and /or / cotton "Q" tips and a degreaser to clean the transistors solder blobs. Blot dry with paper towel .
    It looks like all of your transistor leads are straight in and out of their PCB holes, its just usually just big time production boards that use flow /wave soldering baths and have their leads splayed at an angle a bit.
    Get a damp washcloth /or / cellulose sponge to the ready and tin the tip of a 40-60 watt soldering iron until it shines like "Chrome City". Have the board flat with transistor leads pointing up .
    Put a drop of rosin soldering flux atop each transistor connection, have solder in hand and move in the soldering iron to your first connection and ADD solder . . .up to the size of a BB . . . then
    move in with the cooling option above to cool the warmed joint . Move to the fartherest joint to be the next connection worked on and repeat and then finally do the third and final connection.
    You now have 3 connections floating in solder beads, so now use one hand to grip the transistor to pull out and check the soldering tip for "Chrome City" tinned condition again.
    If OK, then slant the soldering iron tip so that it will touch all 3 solder blobs simultaneously . . . . . and BLAMMMMMMMM . . . . that transistor will pull out, totally free, within 211 milliseconds, immediately, move it up to your lips to blow it cool.

    Then plug in and test.

    We are curious about that mystery transistors pedigree . . . .(Beta)

    Thasssit . . . . .

    73's de Edd
    Last edited by a moderator: Apr 28, 2016
    Anon_LG likes this.
  7. Bastien01


    Apr 17, 2016
    Hi Edd,

    Thanks again for all the tips.
    Yes it just make the image brighter and it also have 3 outputs which is pretty convenient. It also have a fade/wipe function.

    I finally grabbed a transistor tester and desoldered the mysterious transistor, and I think it's not a NPN or PNP, cause I can't get a good beta value, the pointer is going crazy. I tried with 2N3904/06, BC547/57 before and i had correct values, so the tester seems to be working as it should. Any other test I can do since it's not a NPN/PNP?

    I draw the schematic so you can get a better insight on the purpose of this transistor (I'm not sure it's 100% correct, but it should be enough). It's really near the power supply, so i think it may be power related.

    You can find it here:

    The unknown transistor is Q8, it's on the left part of the schematic, I put a NPN as a placeholder.

    I put a socket for the transistor so i can make test more easily, and i tried with various transistor i had around and none seems to fit, the best i had is a really dark image.

    Thanks for your help!

    Last edited: Apr 28, 2016
  8. Bastien01


    Apr 17, 2016
    Hi there,

    I tried with other transistors that i had, and a J310 seems to work, so I think it may be a n-channel JFET.
    I grabbed some vero board, I'll do a circuit to test Vgs and tell you.

    Have a good day!
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