CR 1780 burnt amplifier?

  • Hello,


    Excuse me for writing in English but my German is very poor, i hope this is ok?
    I live in Sweden and read this board mostly by the help of Google translate :)


    I recently bought a Dual CR 1780, visually it looks very good unfortunately one channel on the amplifier board is burnt.



    The components i know is broken (visually and measured) are these:


    R325, R335 (cracked, burnt)
    T312 (cracked, burnt)
    T314 (short C <-> E)
    T310 (short B <-> C <-> E)


    So, what do you think? How much do i need to replace to get this machine running?
    I really want it to work again, so i appreciate any comments and help on this matter.


    I would also be thankful if anyone can suggest replacements for T310 & T314.
    I have verified that the pre-amp is working ok by connecting it to another amp, no problem there.


    (i am used to work with electronics, so i can measure and work (replace components, solder etc.) on the board pretty easily)

    | Thoréns TD-166 mkV | Sony STR-414L | Pioneer SX-626 | Dual CR 1780 | Expert TA 940 | harman/kardon CD91C |

  • Hello Batboy,


    first of all you should know the essential datas of the output transistors:


    Here the 2SB702:
    Pc maxUcb maxUce maxUeb maxIc maxTj max, °CFt maxCc tipHfe125W160V160V5V12A150°C10MHz-35/200



    It's pinning should be B-C-E.



    and the 2SD738A
    Pc maxUcb maxUce maxUeb maxIc maxTj max, °CFt maxCc tipHfe125W160V160V5V12A150°C--30/90



    Then you can look for an equivalent type.


    I fear you must change the transistor housing from XM20 to TO247 or TO3P.
    I had a look at some transistors from On Semi.There you can find some audio power transistors.


    T1312 is used for current limitation in case of output overload.


    Probably you also have to replace the driver stage (T1309 and 1303). In any case you should check them.
    And due to the burned R335 you should check R333 and 334.



    greetings
    Norbert

  • Hallo Batboy,


    The output transistor replacements are 2SC3264 ~ 2SD738 (NPN) and 2SA1295 ~ 2SB702 (PNP) they have almost the same housing and pinning so nothing has to be changed/modified. I used them a few years ago for the replacement of the output stage of my CR1780. I received the brand "Sanken". They are a perfect replacement for the output stage. I saw on the internet that these replacements are still available at FARNELL, they are not cheap ;(




    Greetings,


    Robert

    Bilder

    p300a,1009,1019,1209,1216,1224,1228,1229,1237A,502,504,601,617Q,650,701,704,721,731,741,5000,CV31CV62,CV121CV240,CV1460,CV1462,CT1460,CT1462,CT1540,HS27,HS43,KA50,C814,C839,C844,C846,C901,C919,C939,CD120,CD130,CD40,CL142,CL150,CL172,CL180,CL230,CL710,CL720,CL722,CL730

    Einmal editiert, zuletzt von tillschweiger ()

  • Thanks for your answers.


    I assume it is best practice to replace the transistors on both channels, so they are identical?


    / Joakim

    | Thoréns TD-166 mkV | Sony STR-414L | Pioneer SX-626 | Dual CR 1780 | Expert TA 940 | harman/kardon CD91C |

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